-
Notifications
You must be signed in to change notification settings - Fork 1
Expand file tree
/
Copy pathrails_database_and_model.html
More file actions
718 lines (693 loc) · 59.8 KB
/
rails_database_and_model.html
File metadata and controls
718 lines (693 loc) · 59.8 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
<!doctype html>
<html dir="ltr" lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Rails: Models and Activerecord — Ruby on Rails Guides</title>
<link rel="stylesheet" type="text/css" href="stylesheets/style.css" data-turbo-track="reload">
<link rel="stylesheet" type="text/css" href="stylesheets/print.css" media="print">
<link rel="stylesheet" type="text/css" href="stylesheets/highlight.css" data-turbo-track="reload">
<link rel="icon" href="images/backend-development.svg" sizes="any">
<script src="javascripts/@hotwired--turbo.js" data-turbo-track="reload"></script>
<script src="javascripts/clipboard.js" data-turbo-track="reload"></script>
<script src="javascripts/guides.js" data-turbo-track="reload"></script>
<meta property="og:title" content="Rails: Models and Activerecord — Ruby on Rails Guides" />
<meta name="description" content="Rails: Models and ActiverecordModels are the basic classes of a Rails Project. The data is actually stored in a relational database.After working through this guide you should Be able to use models in the rails console The examples were inspired by "Rails for Zombies", which used to be a free Rails online course. Sadly it is no longer available.When working through this chapter you should be doing the ZombieTwitter Assignment in parallell." />
<meta property="og:description" content="Rails: Models and ActiverecordModels are the basic classes of a Rails Project. The data is actually stored in a relational database.After working through this guide you should Be able to use models in the rails console The examples were inspired by "Rails for Zombies", which used to be a free Rails online course. Sadly it is no longer available.When working through this chapter you should be doing the ZombieTwitter Assignment in parallell." />
<meta property="og:locale" content="en_US" />
<meta property="og:site_name" content="Textbook Backend Developemnt" />
<meta property="og:image" content="images/backend-development.svg" />
<meta property="og:type" content="website" />
<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link href="https://fonts.googleapis.com/css2?family=Noto+Sans+Arabic:wght@100..900&display=swap" rel="stylesheet">
<link href="https://fonts.googleapis.com/css2?family=Heebo:wght@100..900&family=Noto+Sans+Arabic:wght@100..900&display=swap" rel="stylesheet">
<meta name="theme-color" content="#2e56e9">
</head>
<body class="guide">
<header id="page_header">
<div class="wrapper clearfix">
<nav id="feature_nav">
<div class="header-logo">
<a href="/">Backend Development</a>
</div>
<ul class="nav">
<li><a class="nav-item" id="home_nav" href="/">Home</a></li>
<li class="guides-index guides-index-large">
<a href="index.html" id="guidesMenu" class="guides-index-item nav-item">Index</a>
<div id="guides" class="clearfix" style="display: none;">
<hr />
<dl class="guides-section-container">
<div class="guides-section">
<dt>Ruby on Rails</dt>
<dd><a href="ruby_commandline.html">Ruby Commandline</a></dd>
<dd><a href="rails_database_and_model.html">Models and ActiveRecord</a></dd>
<dd><a href="rails_db.html">Database and Migrations</a></dd>
<dd><a href="rails_associations_and_validations.html">Associations and Validations</a></dd>
<dd><a href="rails_view_and_controller.html">Routing, View and Controller</a></dd>
<dd><a href="rails_authentication.html">Simple Authentication</a></dd>
<dd><a href="assets_and_import_map.html">The Asset Pipeline and Importmaps</a></dd>
<dd><a href="testing.html">Getting started with Testing</a></dd>
<dd><a href="refactoring_rails.html">Refactoring Rails</a></dd>
<dd><a href="deploy-to-paas.html">Deploy to PAAS</a></dd>
<dd><a href="rails_gems.html">Ruby Gems for your Rails Project</a></dd>
<dd><a href="deploying_rails.html">Deploying Rails</a></dd>
</div>
<div class="guides-section">
<dt>Ruby on Rails - Advanced Topics</dt>
<dd><a href="deploy-to-paas.html">Deploy to PAAS</a></dd>
<dd><a href="rest-api.html">REST API</a></dd>
<dd><a href="graphql-api.html">GraphQL API</a></dd>
<dd><a href="rails_websockets.html">Websocket in Rails</a></dd>
<dd><a href="jobs_and_tasks.html">Jobs and Tasks in Rails</a></dd>
<dd><a href="rails_security.html">Rails Security</a></dd>
</div>
<div class="guides-section">
<dt>Overarching Concerns</dt>
<dd><a href="issue.html">Issue Lifecycle</a></dd>
<dd><a href="security.html">Security</a></dd>
<dd><a href="adv_authentication.html">Advanced Authentication</a></dd>
<dd><a href="caching.html">Caching</a></dd>
<dd><a href="advanced_testing.html">Advanced Testing</a></dd>
<dd><a href="internationalization.html">Internationalization (I18n)</a></dd>
<dd><a href="git_rebasing.html">Git Rebasing</a></dd>
</div>
<div class="guides-section">
<dt>Nodes.js</dt>
<dd><a href="node_vs_rails.html">Node vs. Rails</a></dd>
<dd><a href="node_basics.html">Node Basics</a></dd>
<dd><a href="node_websockets.html">Node Websockets</a></dd>
<dd><a href="node_express.html">Node Web App</a></dd>
<dd><a href="node_cluster.html">Scaling Node</a></dd>
</div>
<div class="guides-section">
<dt>Next.js</dt>
<dd><a href="nextjs.html">Next.js</a></dd>
</div>
</dl>
</div>
</li>
<li class="guides-index guides-index-small">
<select class="guides-index-item nav-item">
<option value="index.html">Index</option>
<optgroup label="Ruby on Rails">
<option value="ruby_commandline.html">Ruby Commandline</option>
<option value="rails_database_and_model.html">Models and ActiveRecord</option>
<option value="rails_db.html">Database and Migrations</option>
<option value="rails_associations_and_validations.html">Associations and Validations</option>
<option value="rails_view_and_controller.html">Routing, View and Controller</option>
<option value="rails_authentication.html">Simple Authentication</option>
<option value="assets_and_import_map.html">The Asset Pipeline and Importmaps</option>
<option value="testing.html">Getting started with Testing</option>
<option value="refactoring_rails.html">Refactoring Rails</option>
<option value="deploy-to-paas.html">Deploy to PAAS</option>
<option value="rails_gems.html">Ruby Gems for your Rails Project</option>
<option value="deploying_rails.html">Deploying Rails</option>
</optgroup>
<optgroup label="Ruby on Rails - Advanced Topics">
<option value="deploy-to-paas.html">Deploy to PAAS</option>
<option value="rest-api.html">REST API</option>
<option value="graphql-api.html">GraphQL API</option>
<option value="rails_websockets.html">Websocket in Rails</option>
<option value="jobs_and_tasks.html">Jobs and Tasks in Rails</option>
<option value="rails_security.html">Rails Security</option>
</optgroup>
<optgroup label="Overarching Concerns">
<option value="issue.html">Issue Lifecycle</option>
<option value="security.html">Security</option>
<option value="adv_authentication.html">Advanced Authentication</option>
<option value="caching.html">Caching</option>
<option value="advanced_testing.html">Advanced Testing</option>
<option value="internationalization.html">Internationalization (I18n)</option>
<option value="git_rebasing.html">Git Rebasing</option>
</optgroup>
<optgroup label="Nodes.js">
<option value="node_vs_rails.html">Node vs. Rails</option>
<option value="node_basics.html">Node Basics</option>
<option value="node_websockets.html">Node Websockets</option>
<option value="node_express.html">Node Web App</option>
<option value="node_cluster.html">Scaling Node</option>
</optgroup>
<optgroup label="Next.js">
<option value="nextjs.html">Next.js</option>
</optgroup>
</select>
</li>
</ul>
</nav>
</div>
</header>
<hr class="hide" />
<section id="feature">
<div class="wrapper">
<h1>Rails: Models and Activerecord</h1><p>Models are the basic classes of a Rails Project. The
data is actually stored in a relational database.</p><p>After working through this guide you should</p>
<ul>
<li>Be able to use models in the rails console</li>
</ul>
<p>The examples were inspired by "Rails for Zombies", which used to be a free Rails online course.
Sadly it is no longer available.</p><p>When working through this chapter you should be doing the
<a href="https://gitlab.mediacube.at/bjelline/backend-assign-public/-/blob/master/a2_zombietwitter/README.md">ZombieTwitter</a> Assignment in parallell.</p>
<nav id="subCol">
<h3 class="chapter">
<picture>
<!-- Using the `source` HTML tag to set the dark theme image -->
<source
srcset="images/icon_book-close-bookmark-1-wht.svg"
media="(prefers-color-scheme: dark)"
/>
<img src="images/icon_book-close-bookmark-1.svg" alt="Chapter Icon" />
</picture>
Chapters
</h3>
<ol class="chapters">
<li><a href="#model-basics">Model Basics</a>
<ul>
<li><a href="#the-mapping">The Mapping</a></li>
</ul></li>
<li><a href="#the-model">The Model</a>
<ul>
<li><a href="#the-model-in-the-console">The model in the console</a></li>
<li><a href="#finding-a-model">Finding a model</a></li>
<li><a href="#accessing-the-properties">Accessing the properties</a></li>
<li><a href="#crud-create-read-update-delete">CRUD = Create, Read, Update, Delete</a></li>
<li><a href="#create">Create</a></li>
<li><a href="#read">Read</a></li>
<li><a href="#update">Update</a></li>
<li><a href="#delete">Delete</a></li>
<li><a href="#chaining-activerecord-methods">Chaining ActiveRecord methods</a></li>
<li><a href="#further-reading">Further reading</a></li>
</ul></li>
</ol>
</nav>
<hr>
</div>
</section>
<main id="container">
<div class="wrapper">
<div id="mainCol">
<div class='slide'>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-0' href='slides_rails_database_and_model.html#/0'>◻</a></p>
<h2 id="model-basics"><a class="anchorlink" href="#model-basics"><span>1</span> Model Basics</a></h2><p>Rails Models are classes that represent tables in the database.</p><p>Rails implements the Active Record pattern in a class called <code>ActiveRecord</code>.
All the models in a Rails project inherit from <code>ActiveRecord</code>.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="c1"># file app/models/Tweet.rb</span>
<span class="c1"># this is the Tweet model that you create</span>
<span class="k">class</span> <span class="nc">Tweet</span> <span class="o"><</span> <span class="no">ApplicationRecord</span>
<span class="k">end</span>
<span class="c1"># file app/models/application_record.rb</span>
<span class="c1"># this file already exists</span>
<span class="k">class</span> <span class="nc">ApplicationRecord</span> <span class="o"><</span> <span class="no">ActiveRecord</span><span class="o">::</span><span class="no">Base</span>
<span class="n">primary_abstract_class</span>
<span class="k">end</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="# file app/models/Tweet.rb
# this is the Tweet model that you create
class Tweet < ApplicationRecord
end
# file app/models/application_record.rb
# this file already exists
class ApplicationRecord < ActiveRecord::Base
primary_abstract_class
end
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-1' href='slides_rails_database_and_model.html#/1'>◻</a></p>
<h3 id="the-mapping"><a class="anchorlink" href="#the-mapping"><span>1.1</span> The Mapping</a></h3><p>A quick overview of how Objects and Database relate when using
ActiveRecord in Rails:</p><div class="interstitial code">
<pre><code class="highlight plaintext">Database Ruby on Rails
--------------------------- --------------------------
table courses class Course
in the Database in file app/models/course.rb
one row in the table one object of the class Course
an attibute in the table a property of the object
SELECT * FROM courses WHERE id=7 Course.find(7)
</code></pre>
<button class="clipboard-button" data-clipboard-text="Database Ruby on Rails
--------------------------- --------------------------
table courses class Course
in the Database in file app/models/course.rb
one row in the table one object of the class Course
an attibute in the table a property of the object
SELECT * FROM courses WHERE id=7 Course.find(7)
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-2' href='slides_rails_database_and_model.html#/2'>◻</a></p>
<h2 id="the-model"><a class="anchorlink" href="#the-model"><span>2</span> The Model</a></h2><p>Look at the model generated in file <code>app/models/tweet.rb</code>. Later you will add validations, associations to other models and the business logic here.</p></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-3' href='slides_rails_database_and_model.html#/3'>◻</a></p>
<h3 id="the-model-in-the-console"><a class="anchorlink" href="#the-model-in-the-console"><span>2.1</span> The model in the console</a></h3><p>You can use the Rails console to work with
the model interactively. This is similar to the ruby console <code>irb</code>
but with your Rails app already loaded.
Any changes you make are really written
to the development database!</p>
<ul>
<li><code>rails console</code></li>
</ul>
<p>if you just want to play around and not make changes to the database use</p>
<ul>
<li><code>rails console --sandbox</code></li>
</ul>
<p>instead.</p></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-4' href='slides_rails_database_and_model.html#/4'>◻</a></p>
<h3 id="finding-a-model"><a class="anchorlink" href="#finding-a-model"><span>2.2</span> Finding a model</a></h3><p>The database table always has a primary key <code>id</code>. You can use this
key to find a specific record:</p><p><img src="images/rails_console_find.png" alt="using find in the Rails console"></p><p>When you type in <code>Tweet.find(1)</code> into the Rails console, you get two answers:</p><p>First (in color) it shows you the SQL query sent to the database. In this case
<code>SELECT "tweets".* FROM "tweets" WHERE "tweets"."id" = ? LIMIT ?</code>. You can see
that prepared statements are used, and that a limit is always placed on the number
of answers.</p><p>After the Arrow (<code>=></code>) the Rails console shows the return value of the command
you typed in. Here this is an object. The console prints out the details of this
object using the <code>inspect</code> method.</p></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-5' href='slides_rails_database_and_model.html#/5'>◻</a></p>
<p>From now on we will use this slightly shortended format to show Rails console
input and output:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">find</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="o">=></span>
<span class="c1">#<Tweet:0x0000000105308f58</span>
<span class="ss">id: </span><span class="mi">1</span><span class="p">,</span>
<span class="ss">status: </span><span class="s2">"Where can I get a good bite to eat?"</span><span class="p">,</span>
<span class="ss">zombie: </span><span class="s2">"Ash"</span><span class="p">,</span>
<span class="ss">created_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.955788000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="p">,</span>
<span class="ss">updated_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.955788000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="o">></span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> Tweet.find(1)
=>
#<Tweet:0x0000000105308f58
id: 1,
status: "Where can I get a good bite to eat?",
zombie: "Ash",
created_at: Sun, 22 Oct 2023 14:54:27.955788000 UTC +00:00,
updated_at: Sun, 22 Oct 2023 14:54:27.955788000 UTC +00:00>
">Copy</button>
</div>
<p>(We will leave out the SQL, and some timestamps.)</p></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-6' href='slides_rails_database_and_model.html#/6'>◻</a></p>
<h3 id="accessing-the-properties"><a class="anchorlink" href="#accessing-the-properties"><span>2.3</span> Accessing the properties</a></h3><p>You can access the properties of the model object as if it were a hash
or through method names:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">find</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="o">=></span> <span class="c1">#<Tweet id: 3, status: "I just ate some delicious brains.", zombie: "Jim"></span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">.</span><span class="nf">status</span>
<span class="o">=></span> <span class="s2">"I just ate some delicious brains."</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">[</span><span class="ss">:status</span><span class="p">]</span>
<span class="o">=></span> <span class="s2">"I just ate some delicious brains."</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">.</span><span class="nf">zombie</span>
<span class="o">=></span> <span class="s2">"Jim"</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">[</span><span class="ss">:zombie</span><span class="p">]</span>
<span class="o">=></span> <span class="s2">"Jim"</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> t = Tweet.find(3)
=> #<Tweet id: 3, status: "I just ate some delicious brains.", zombie: "Jim">
railsconsole> t.status
=> "I just ate some delicious brains."
railsconsole> t[:status]
=> "I just ate some delicious brains."
railsconsole> t.zombie
=> "Jim"
railsconsole> t[:zombie]
=> "Jim"
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-7' href='slides_rails_database_and_model.html#/7'>◻</a></p>
<h3 id="crud-create-read-update-delete"><a class="anchorlink" href="#crud-create-read-update-delete"><span>2.4</span> CRUD = Create, Read, Update, Delete</a></h3><p>Let's see how ActiveRecord implements the four important
capabilities of persistance:</p></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-8' href='slides_rails_database_and_model.html#/8'>◻</a></p>
<h3 id="create"><a class="anchorlink" href="#create"><span>2.5</span> Create</a></h3><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">t</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">new</span>
<span class="n">t</span><span class="p">.</span><span class="nf">status</span> <span class="o">=</span> <span class="s2">"I <3 brains."</span>
<span class="n">t</span><span class="p">.</span><span class="nf">save</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="t = Tweet.new
t.status = "I <3 brains."
t.save
">Copy</button>
</div>
<p>With <code>new</code> you create a new object just in memory. It is not stored in the
database yet and does not have an <code>id</code> yet. You can set its properties.
The <code>save</code> method tries to save it to the database.</p></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-9' href='slides_rails_database_and_model.html#/9'>◻</a></p>
<p>On the Rails console you can see how the properties are <code>nil</code> in the beginning.
After saving to the database some of the properties are set:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">new</span>
<span class="o">=></span> <span class="c1">#<Tweet:0x0000000106688358 id: nil, status: nil, zombie: nil, created_at: nil, updated_at: nil></span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">.</span><span class="nf">status</span> <span class="o">=</span> <span class="s2">"I <3 brains."</span>
<span class="o">=></span> <span class="s2">"I <3 brains."</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">.</span><span class="nf">save</span>
<span class="no">TRANSACTION</span> <span class="p">(</span><span class="mf">3.8</span><span class="n">ms</span><span class="p">)</span> <span class="k">BEGIN</span>
<span class="no">Tweet</span> <span class="no">Create</span> <span class="p">(</span><span class="mf">9.2</span><span class="n">ms</span><span class="p">)</span> <span class="no">INSERT</span> <span class="no">INTO</span> <span class="s2">"tweets"</span> <span class="p">(</span><span class="s2">"status"</span><span class="p">,</span> <span class="s2">"zombie"</span><span class="p">,</span> <span class="s2">"created_at"</span><span class="p">,</span> <span class="s2">"updated_at"</span><span class="p">)</span> <span class="no">VALUES</span> <span class="p">(</span><span class="vg">$1</span><span class="p">,</span> <span class="vg">$2</span><span class="p">,</span> <span class="vg">$3</span><span class="p">,</span> <span class="vg">$4</span><span class="p">)</span> <span class="no">RETURNING</span> <span class="s2">"id"</span> <span class="p">[[</span><span class="s2">"status"</span><span class="p">,</span> <span class="s2">"I <3 brains."</span><span class="p">],</span> <span class="p">[</span><span class="s2">"zombie"</span><span class="p">,</span> <span class="kp">nil</span><span class="p">],</span> <span class="p">[</span><span class="s2">"created_at"</span><span class="p">,</span> <span class="s2">"2023-10-22 17:12:31.990939"</span><span class="p">],</span> <span class="p">[</span><span class="s2">"updated_at"</span><span class="p">,</span> <span class="s2">"2023-10-22 17:12:31.990939"</span><span class="p">]]</span>
<span class="no">TRANSACTION</span> <span class="p">(</span><span class="mf">2.0</span><span class="n">ms</span><span class="p">)</span> <span class="no">COMMIT</span>
<span class="o">=></span> <span class="kp">true</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span>
<span class="o">=></span>
<span class="c1">#<Tweet:0x0000000106688358</span>
<span class="ss">id: </span><span class="mi">4</span><span class="p">,</span>
<span class="ss">status: </span><span class="s2">"I <3 brains."</span><span class="p">,</span>
<span class="ss">zombie: </span><span class="kp">nil</span><span class="p">,</span>
<span class="ss">created_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">17</span><span class="p">:</span><span class="mi">12</span><span class="p">:</span><span class="mf">31.990939000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="p">,</span>
<span class="ss">updated_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">17</span><span class="p">:</span><span class="mi">12</span><span class="p">:</span><span class="mf">31.990939000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="o">></span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> t = Tweet.new
=> #<Tweet:0x0000000106688358 id: nil, status: nil, zombie: nil, created_at: nil, updated_at: nil>
railsconsole> t.status = "I <3 brains."
=> "I <3 brains."
railsconsole> t.save
TRANSACTION (3.8ms) BEGIN
Tweet Create (9.2ms) INSERT INTO "tweets" ("status", "zombie", "created_at", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id" [["status", "I <3 brains."], ["zombie", nil], ["created_at", "2023-10-22 17:12:31.990939"], ["updated_at", "2023-10-22 17:12:31.990939"]]
TRANSACTION (2.0ms) COMMIT
=> true
railsconsole> t
=>
#<Tweet:0x0000000106688358
id: 4,
status: "I <3 brains.",
zombie: nil,
created_at: Sun, 22 Oct 2023 17:12:31.990939000 UTC +00:00,
updated_at: Sun, 22 Oct 2023 17:12:31.990939000 UTC +00:00>
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-10' href='slides_rails_database_and_model.html#/10'>◻</a></p>
<h3 id="read"><a class="anchorlink" href="#read"><span>2.6</span> Read</a></h3><p>There are many ways to read data from the database. We already saw <code>find</code> which
uses the primary key and always returns one object. The method <code>where</code> is used for more general <code>select - where</code> SQL statements.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">t1</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">find</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="n">t2</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">where</span><span class="p">(</span><span class="s2">"created_at > '2023-10-21'"</span><span class="p">)</span>
<span class="n">t3</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">where</span><span class="p">(</span><span class="ss">zombie: </span><span class="s1">'Ash'</span><span class="p">)</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="t1 = Tweet.find(3)
t2 = Tweet.where("created_at > '2023-10-21'")
t3 = Tweet.where(zombie: 'Ash')
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-11' href='slides_rails_database_and_model.html#/11'>◻</a></p>
<p>In the Rails console you can see the return values: <code>where</code> returns serveral objects in the end.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="n">t2</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">where</span><span class="p">(</span><span class="s2">"created_at > '2023-10-21'"</span><span class="p">)</span>
<span class="no">Tweet</span> <span class="no">Load</span> <span class="p">(</span><span class="mf">1.0</span><span class="n">ms</span><span class="p">)</span> <span class="no">SELECT</span> <span class="s2">"tweets"</span><span class="p">.</span><span class="nf">*</span> <span class="no">FROM</span> <span class="s2">"tweets"</span> <span class="no">WHERE</span> <span class="p">(</span><span class="n">created_at</span> <span class="o">></span> <span class="s1">'2023-10-21'</span><span class="p">)</span>
<span class="o">=></span>
<span class="p">[</span><span class="c1">#<Tweet:0x00000001066070a0</span>
<span class="o">...</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t2</span>
<span class="o">=></span>
<span class="p">[</span><span class="c1">#<Tweet:0x00000001066070a0</span>
<span class="ss">id: </span><span class="mi">1</span><span class="p">,</span>
<span class="ss">status: </span><span class="s2">"Where can I get a good bite to eat?"</span><span class="p">,</span>
<span class="ss">zombie: </span><span class="s2">"Ash"</span><span class="p">,</span>
<span class="ss">created_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.955788000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="p">,</span>
<span class="ss">updated_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.955788000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="o">></span><span class="p">,</span>
<span class="c1">#<Tweet:0x0000000106606f60</span>
<span class="ss">id: </span><span class="mi">2</span><span class="p">,</span>
<span class="ss">status: </span><span class="s2">"I <3 brains."</span><span class="p">,</span>
<span class="ss">zombie: </span><span class="s2">"QueenRotten"</span><span class="p">,</span>
<span class="ss">created_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.957318000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="p">,</span>
<span class="ss">updated_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.957318000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="o">></span><span class="p">,</span>
<span class="c1">#<Tweet:0x0000000106606e20</span>
<span class="ss">id: </span><span class="mi">3</span><span class="p">,</span>
<span class="ss">status: </span><span class="s2">"I just ate some delicious brains."</span><span class="p">,</span>
<span class="ss">zombie: </span><span class="s2">"Jim"</span><span class="p">,</span>
<span class="ss">created_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.958430000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="p">,</span>
<span class="ss">updated_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.958430000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="o">></span><span class="p">,</span>
<span class="c1">#<Tweet:0x0000000106606ce0</span>
<span class="ss">id: </span><span class="mi">4</span><span class="p">,</span>
<span class="ss">status: </span><span class="s2">"I <3 brains."</span><span class="p">,</span>
<span class="ss">zombie: </span><span class="kp">nil</span><span class="p">,</span>
<span class="ss">created_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">17</span><span class="p">:</span><span class="mi">12</span><span class="p">:</span><span class="mf">31.990939000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="p">,</span>
<span class="ss">updated_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">17</span><span class="p">:</span><span class="mi">12</span><span class="p">:</span><span class="mf">31.990939000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="o">></span><span class="p">]</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> t2 = Tweet.where("created_at > '2023-10-21'")
Tweet Load (1.0ms) SELECT "tweets".* FROM "tweets" WHERE (created_at > '2023-10-21')
=>
[#<Tweet:0x00000001066070a0
...
railsconsole> t2
=>
[#<Tweet:0x00000001066070a0
id: 1,
status: "Where can I get a good bite to eat?",
zombie: "Ash",
created_at: Sun, 22 Oct 2023 14:54:27.955788000 UTC +00:00,
updated_at: Sun, 22 Oct 2023 14:54:27.955788000 UTC +00:00>,
#<Tweet:0x0000000106606f60
id: 2,
status: "I <3 brains.",
zombie: "QueenRotten",
created_at: Sun, 22 Oct 2023 14:54:27.957318000 UTC +00:00,
updated_at: Sun, 22 Oct 2023 14:54:27.957318000 UTC +00:00>,
#<Tweet:0x0000000106606e20
id: 3,
status: "I just ate some delicious brains.",
zombie: "Jim",
created_at: Sun, 22 Oct 2023 14:54:27.958430000 UTC +00:00,
updated_at: Sun, 22 Oct 2023 14:54:27.958430000 UTC +00:00>,
#<Tweet:0x0000000106606ce0
id: 4,
status: "I <3 brains.",
zombie: nil,
created_at: Sun, 22 Oct 2023 17:12:31.990939000 UTC +00:00,
updated_at: Sun, 22 Oct 2023 17:12:31.990939000 UTC +00:00>]
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-12' href='slides_rails_database_and_model.html#/12'>◻</a></p>
<h3 id="update"><a class="anchorlink" href="#update"><span>2.7</span> Update</a></h3><p>With update - as with <code>new</code> before - we see the difference between the
object in memory (<code>t</code>) which can be changed and the object in the database
which is only changed when t is saved back to the database.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">t</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">find</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="n">t</span><span class="p">.</span><span class="nf">zombie</span> <span class="o">=</span> <span class="s2">"EyeballChomper"</span>
<span class="n">t</span><span class="p">.</span><span class="nf">save</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="t = Tweet.find(3)
t.zombie = "EyeballChomper"
t.save
">Copy</button>
</div>
<p>In the Rails console you can see that the UPDATE statement in SQL really
only changes the one changed attribute.
Plus the property <code>updated_at</code> is automatically set.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">find</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="no">Tweet</span> <span class="no">Load</span> <span class="p">(</span><span class="mf">10.0</span><span class="n">ms</span><span class="p">)</span> <span class="no">SELECT</span> <span class="s2">"tweets"</span><span class="p">.</span><span class="nf">*</span> <span class="no">FROM</span> <span class="s2">"tweets"</span> <span class="no">WHERE</span> <span class="s2">"tweets"</span><span class="o">.</span><span class="s2">"id"</span> <span class="o">=</span> <span class="vg">$1</span> <span class="no">LIMIT</span> <span class="vg">$2</span> <span class="p">[[</span><span class="s2">"id"</span><span class="p">,</span> <span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="s2">"LIMIT"</span><span class="p">,</span> <span class="mi">1</span><span class="p">]]</span>
<span class="o">=></span>
<span class="c1">#<Tweet:0x0000000106603ae0</span>
<span class="o">...</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">.</span><span class="nf">zombie</span> <span class="o">=</span> <span class="s2">"EyeballChomper"</span>
<span class="o">=></span> <span class="s2">"EyeballChomper"</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">.</span><span class="nf">save</span>
<span class="no">TRANSACTION</span> <span class="p">(</span><span class="mf">4.6</span><span class="n">ms</span><span class="p">)</span> <span class="k">BEGIN</span>
<span class="no">Tweet</span> <span class="no">Update</span> <span class="p">(</span><span class="mf">18.0</span><span class="n">ms</span><span class="p">)</span> <span class="no">UPDATE</span> <span class="s2">"tweets"</span> <span class="no">SET</span> <span class="s2">"zombie"</span> <span class="o">=</span> <span class="vg">$1</span><span class="p">,</span> <span class="s2">"updated_at"</span> <span class="o">=</span> <span class="vg">$2</span> <span class="no">WHERE</span> <span class="s2">"tweets"</span><span class="o">.</span><span class="s2">"id"</span> <span class="o">=</span> <span class="vg">$3</span> <span class="p">[[</span><span class="s2">"zombie"</span><span class="p">,</span> <span class="s2">"EyeballChomper"</span><span class="p">],</span> <span class="p">[</span><span class="s2">"updated_at"</span><span class="p">,</span> <span class="s2">"2023-10-22 17:17:34.242526"</span><span class="p">],</span> <span class="p">[</span><span class="s2">"id"</span><span class="p">,</span> <span class="mi">3</span><span class="p">]]</span>
<span class="no">TRANSACTION</span> <span class="p">(</span><span class="mf">0.9</span><span class="n">ms</span><span class="p">)</span> <span class="no">COMMIT</span>
<span class="o">=></span> <span class="kp">true</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> t = Tweet.find(3)
Tweet Load (10.0ms) SELECT "tweets".* FROM "tweets" WHERE "tweets"."id" = $1 LIMIT $2 [["id", 3], ["LIMIT", 1]]
=>
#<Tweet:0x0000000106603ae0
...
railsconsole> t.zombie = "EyeballChomper"
=> "EyeballChomper"
railsconsole> t.save
TRANSACTION (4.6ms) BEGIN
Tweet Update (18.0ms) UPDATE "tweets" SET "zombie" = $1, "updated_at" = $2 WHERE "tweets"."id" = $3 [["zombie", "EyeballChomper"], ["updated_at", "2023-10-22 17:17:34.242526"], ["id", 3]]
TRANSACTION (0.9ms) COMMIT
=> true
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-13' href='slides_rails_database_and_model.html#/13'>◻</a></p>
<h3 id="delete"><a class="anchorlink" href="#delete"><span>2.8</span> Delete</a></h3><p>To delete both the object in memory and in the database use <code>destroy</code>.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">t</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">find</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="n">t</span><span class="p">.</span><span class="nf">destroy</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="t = Tweet.find(3)
t.destroy
">Copy</button>
</div>
<p>On the console you can see how <code>destroy</code> is translated to <code>DELETE</code> in SQL.
<code>destroy</code> gives the last version of the model as a return value.</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">find</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="no">Tweet</span> <span class="no">Load</span> <span class="p">(</span><span class="mf">12.4</span><span class="n">ms</span><span class="p">)</span> <span class="no">SELECT</span> <span class="s2">"tweets"</span><span class="p">.</span><span class="nf">*</span> <span class="no">FROM</span> <span class="s2">"tweets"</span> <span class="no">WHERE</span> <span class="s2">"tweets"</span><span class="o">.</span><span class="s2">"id"</span> <span class="o">=</span> <span class="vg">$1</span> <span class="no">LIMIT</span> <span class="vg">$2</span> <span class="p">[[</span><span class="s2">"id"</span><span class="p">,</span> <span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="s2">"LIMIT"</span><span class="p">,</span> <span class="mi">1</span><span class="p">]]</span>
<span class="o">=></span>
<span class="c1">#<Tweet:0x0000000106600b60</span>
<span class="o">...</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t</span><span class="p">.</span><span class="nf">destroy</span>
<span class="no">TRANSACTION</span> <span class="p">(</span><span class="mf">2.3</span><span class="n">ms</span><span class="p">)</span> <span class="k">BEGIN</span>
<span class="no">Tweet</span> <span class="no">Destroy</span> <span class="p">(</span><span class="mf">3.5</span><span class="n">ms</span><span class="p">)</span> <span class="no">DELETE</span> <span class="no">FROM</span> <span class="s2">"tweets"</span> <span class="no">WHERE</span> <span class="s2">"tweets"</span><span class="o">.</span><span class="s2">"id"</span> <span class="o">=</span> <span class="vg">$1</span> <span class="p">[[</span><span class="s2">"id"</span><span class="p">,</span> <span class="mi">3</span><span class="p">]]</span>
<span class="no">TRANSACTION</span> <span class="p">(</span><span class="mf">1.1</span><span class="n">ms</span><span class="p">)</span> <span class="no">COMMIT</span>
<span class="o">=></span>
<span class="c1">#<Tweet:0x0000000106600b60</span>
<span class="ss">id: </span><span class="mi">3</span><span class="p">,</span>
<span class="ss">status: </span><span class="s2">"I just ate some delicious brains."</span><span class="p">,</span>
<span class="ss">zombie: </span><span class="s2">"EyeballChomper"</span><span class="p">,</span>
<span class="ss">created_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">14</span><span class="p">:</span><span class="mi">54</span><span class="p">:</span><span class="mf">27.958430000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="p">,</span>
<span class="ss">updated_at: </span><span class="no">Sun</span><span class="p">,</span> <span class="mi">22</span> <span class="no">Oct</span> <span class="mi">2023</span> <span class="mi">17</span><span class="p">:</span><span class="mi">17</span><span class="p">:</span><span class="mf">34.242526000</span> <span class="no">UTC</span> <span class="o">+</span><span class="mo">00</span><span class="p">:</span><span class="mo">00</span><span class="o">></span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> t = Tweet.find(3)
Tweet Load (12.4ms) SELECT "tweets".* FROM "tweets" WHERE "tweets"."id" = $1 LIMIT $2 [["id", 3], ["LIMIT", 1]]
=>
#<Tweet:0x0000000106600b60
...
railsconsole> t.destroy
TRANSACTION (2.3ms) BEGIN
Tweet Destroy (3.5ms) DELETE FROM "tweets" WHERE "tweets"."id" = $1 [["id", 3]]
TRANSACTION (1.1ms) COMMIT
=>
#<Tweet:0x0000000106600b60
id: 3,
status: "I just ate some delicious brains.",
zombie: "EyeballChomper",
created_at: Sun, 22 Oct 2023 14:54:27.958430000 UTC +00:00,
updated_at: Sun, 22 Oct 2023 17:17:34.242526000 UTC +00:00>
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-14' href='slides_rails_database_and_model.html#/14'>◻</a></p>
<h3 id="chaining-activerecord-methods"><a class="anchorlink" href="#chaining-activerecord-methods"><span>2.9</span> Chaining ActiveRecord methods</a></h3><p>Let's look at the example of using <code>where</code> again: the return value was of class <code>ActiveRecord::Relation</code>:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="n">t3</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">where</span><span class="p">(</span><span class="ss">zombie: </span><span class="s1">'Ash'</span><span class="p">)</span>
<span class="no">Tweet</span> <span class="no">Load</span> <span class="p">(</span><span class="mf">9.6</span><span class="n">ms</span><span class="p">)</span> <span class="no">SELECT</span> <span class="s2">"tweets"</span><span class="p">.</span><span class="nf">*</span> <span class="no">FROM</span> <span class="s2">"tweets"</span> <span class="no">WHERE</span> <span class="s2">"tweets"</span><span class="o">.</span><span class="s2">"zombie"</span> <span class="o">=</span> <span class="vg">$1</span> <span class="p">[[</span><span class="s2">"zombie"</span><span class="p">,</span> <span class="s2">"Ash"</span><span class="p">]]</span>
<span class="o">=></span>
<span class="p">[</span><span class="c1">#<Tweet:0x00000001062858c8</span>
<span class="o">...</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">t3</span><span class="p">.</span><span class="nf">class</span>
<span class="o">=></span> <span class="no">Tweet</span><span class="o">::</span><span class="no">ActiveRecord_Relation</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> t3 = Tweet.where(zombie: 'Ash')
Tweet Load (9.6ms) SELECT "tweets".* FROM "tweets" WHERE "tweets"."zombie" = $1 [["zombie", "Ash"]]
=>
[#<Tweet:0x00000001062858c8
...
railsconsole> t3.class
=> Tweet::ActiveRecord_Relation
">Copy</button>
</div>
<p>This class also supports all the ActiveRecord methods. This means
we can chain several <code>where</code>s together. ActiveRecord can combine them
into a complete SQL statement:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="n">tweets</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">where</span><span class="p">(</span><span class="s2">"created_at > '2023-10-21'"</span><span class="p">).</span><span class="nf">where</span><span class="p">(</span><span class="ss">zombie: </span><span class="s1">'Ash'</span><span class="p">)</span>
<span class="no">Tweet</span> <span class="no">Load</span> <span class="p">(</span><span class="mf">1.0</span><span class="n">ms</span><span class="p">)</span> <span class="no">SELECT</span> <span class="s2">"tweets"</span><span class="p">.</span><span class="nf">*</span> <span class="no">FROM</span> <span class="s2">"tweets"</span> <span class="no">WHERE</span> <span class="p">(</span><span class="n">created_at</span> <span class="o">></span> <span class="s1">'2023-10-21'</span><span class="p">)</span> <span class="no">AND</span> <span class="s2">"tweets"</span><span class="o">.</span><span class="s2">"zombie"</span> <span class="o">=</span> <span class="vg">$1</span> <span class="p">[[</span><span class="s2">"zombie"</span><span class="p">,</span> <span class="s2">"Ash"</span><span class="p">]]</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> tweets = Tweet.where("created_at > '2023-10-21'").where(zombie: 'Ash')
Tweet Load (1.0ms) SELECT "tweets".* FROM "tweets" WHERE (created_at > '2023-10-21') AND "tweets"."zombie" = $1 [["zombie", "Ash"]]
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-15' href='slides_rails_database_and_model.html#/15'>◻</a></p>
<p>In fact there are many more methods we might want to use for chaining:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="no">Tweet</span><span class="p">.</span><span class="nf">limit</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="no">Tweet</span><span class="p">.</span><span class="nf">order</span><span class="p">(</span><span class="ss">:zombie</span><span class="p">)</span>
<span class="no">Tweet</span><span class="p">.</span><span class="nf">select</span><span class="p">(</span><span class="ss">:created_at</span><span class="p">,</span> <span class="ss">:zombie</span><span class="p">,</span> <span class="ss">:status</span><span class="p">)</span>
<span class="no">Tweet</span><span class="p">.</span><span class="nf">where</span><span class="p">(</span><span class="s2">"created_at > '2023-10-21'"</span><span class="p">).</span>
<span class="nf">where</span><span class="p">(</span><span class="ss">zombie: </span><span class="s1">'Ash'</span><span class="p">).</span>
<span class="nf">order</span><span class="p">(</span><span class="ss">:zombie</span><span class="p">).</span><span class="nf">limit</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="Tweet.limit(3)
Tweet.order(:zombie)
Tweet.select(:created_at, :zombie, :status)
Tweet.where("created_at > '2023-10-21'").
where(zombie: 'Ash').
order(:zombie).limit(3)
">Copy</button>
</div>
<p>For the last three lines: Normally the dot is placed in front of the method when chaining. Here
it is placed at the end, to enable copy-and-paste to the Rails console)</p></div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-16' href='slides_rails_database_and_model.html#/16'>◻</a></p>
<p>You can use the method <code>to_sql</code> to see the SQL Statement produced by the chained methods:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">select</span><span class="p">(</span><span class="ss">:created_at</span><span class="p">,</span> <span class="ss">:zombie</span><span class="p">,</span> <span class="ss">:status</span><span class="p">).</span>
<span class="nf">where</span><span class="p">(</span><span class="s2">"created_at > '2020-10-01'"</span><span class="p">).</span>
<span class="nf">where</span><span class="p">(</span><span class="ss">zombie: </span><span class="s1">'Ash'</span><span class="p">).</span>
<span class="nf">order</span><span class="p">(</span><span class="ss">:zombie</span><span class="p">).</span>
<span class="nf">limit</span><span class="p">(</span><span class="mi">3</span><span class="p">).</span><span class="nf">to_sql</span>
<span class="o">=></span> <span class="no">SELECT</span> <span class="s2">"created_at"</span><span class="p">,</span> <span class="s2">"zombie"</span><span class="p">,</span> <span class="s2">"status"</span>
<span class="no">FROM</span> <span class="s2">"tweets"</span>
<span class="no">WHERE</span> <span class="p">(</span><span class="n">created_at</span> <span class="o">></span> <span class="s1">'2020-10-01'</span><span class="p">)</span>
<span class="no">AND</span> <span class="s2">"zombie"</span> <span class="o">=</span> <span class="s1">'Ash'</span>
<span class="no">ORDER</span> <span class="no">BY</span> <span class="s2">"zombie"</span> <span class="no">ASC</span>
<span class="no">LIMIT</span> <span class="mi">3</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> Tweet.select(:created_at, :zombie, :status).
where("created_at > '2020-10-01'").
where(zombie: 'Ash').
order(:zombie).
limit(3).to_sql
=> SELECT "created_at", "zombie", "status"
FROM "tweets"
WHERE (created_at > '2020-10-01')
AND "zombie" = 'Ash'
ORDER BY "zombie" ASC
LIMIT 3
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-17' href='slides_rails_database_and_model.html#/17'>◻</a></p>
<p>The order of the methods is not relevant. You can also save an intermediate step to
a variable, and then chain more methods to that variable later on:</p><div class="interstitial code">
<pre><code class="highlight ruby"><span class="n">railsconsole</span><span class="o">></span> <span class="n">query</span> <span class="o">=</span> <span class="no">Tweet</span><span class="p">.</span><span class="nf">where</span><span class="p">(</span><span class="s2">"created_at > '2020-10-01'"</span><span class="p">).</span>
<span class="nf">order</span><span class="p">(</span><span class="ss">:zombie</span><span class="p">).</span><span class="nf">limit</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="n">railsconsole</span><span class="o">></span> <span class="n">query</span><span class="p">.</span><span class="nf">select</span><span class="p">(</span><span class="ss">:created_at</span><span class="p">,</span> <span class="ss">:zombie</span><span class="p">,</span> <span class="ss">:status</span><span class="p">).</span>
<span class="nf">where</span><span class="p">(</span><span class="ss">zombie: </span><span class="s1">'Ash'</span><span class="p">).</span><span class="nf">to_sql</span>
<span class="o">=></span> <span class="no">SELECT</span> <span class="s2">"created_at"</span><span class="p">,</span> <span class="s2">"zombie"</span><span class="p">,</span> <span class="s2">"status"</span>
<span class="no">FROM</span> <span class="s2">"tweets"</span>
<span class="no">WHERE</span> <span class="p">(</span><span class="n">created_at</span> <span class="o">></span> <span class="s1">'2020-10-01'</span><span class="p">)</span>
<span class="no">AND</span> <span class="s2">"zombie"</span> <span class="o">=</span> <span class="s1">'Ash'</span>
<span class="no">ORDER</span> <span class="no">BY</span> <span class="s2">"zombie"</span> <span class="no">ASC</span>
<span class="no">LIMIT</span> <span class="mi">3</span>
</code></pre>
<button class="clipboard-button" data-clipboard-text="railsconsole> query = Tweet.where("created_at > '2020-10-01'").
order(:zombie).limit(3)
railsconsole> query.select(:created_at, :zombie, :status).
where(zombie: 'Ash').to_sql
=> SELECT "created_at", "zombie", "status"
FROM "tweets"
WHERE (created_at > '2020-10-01')
AND "zombie" = 'Ash'
ORDER BY "zombie" ASC
LIMIT 3
">Copy</button>
</div>
</div>
<div class='slide'>
<p class='slide_break_block'><a class='slide_break' id='slide-18' href='slides_rails_database_and_model.html#/18'>◻</a></p>
<h3 id="further-reading"><a class="anchorlink" href="#further-reading"><span>2.10</span> Further reading</a></h3>
<ul>
<li>The Rails Guides give a good introduction to a subject area:
<ul>
<li>Rails Guide: <a href="https://guides.rubyonrails.org/active_record_basics.html">Active Record Basics</a></li>
<li>Rails Guide: <a href="https://guides.rubyonrails.org/active_record_querying.html">Active Record Query Interface</a></li>
</ul></li>
<li>Use the <a href="https://edgeapi.rubyonrails.org/">Rails API</a> documentation to look up the details:
<ul>
<li><a href="https://edgeapi.rubyonrails.org/classes/ActiveRecord/FinderMethods.html#method-i-find">find</a></li>
<li><a href="https://edgeapi.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-where">where</a></li>
</ul></li>
</ul>
</div>
</div>
</div>
</main>
<hr class="hide" />
<footer id="page_footer">
<div class="wrapper">
<p class="copyright">published under <a href="https://creativecommons.org/licenses/by-nc-sa/3.0/at/deed.de">creative commons by-nc-sa</a> in 2012-2025 by <a href="https://brigitte-jellinek.at">Brigitte Jellinek</a>.
</p>
<p>If you want to contribute: <a href="https://github.com/backend-development/backend-development-textbook/fork">fork the source on github</a>
</p>
<p>Favicon "backend development" by Arkinasi from <a href="https://thenounproject.com/browse/icons/term/backend-development/" target="_blank" title="backend development Icons">Noun Project</a> (CC BY 3.0)</p>
</div>
</footer>
</body>
</html>