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<!DOCTYPE html>
<html lang="en">
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<meta charset="utf-8">
<title>Slides for
Rails: Models and Activerecord — Ruby on Rails Guides
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<!-- Any section element inside of this container is displayed as a slide -->
<div class="slides">
<section>
<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>
<p><small>Slides - use arrow keys to navigate, esc to return to page view, f for fullscreen</small></p>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-0'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-1'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-2'>▻</a>
<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></section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-3'>▻</a>
<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></section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-4'>▻</a>
<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></section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-5'>▻</a>
<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></section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-6'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-7'>▻</a>
<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></section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-8'>▻</a>
<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></section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-9'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-10'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-11'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-12'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-13'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-14'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-15'>▻</a>
<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></section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-16'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-17'>▻</a>
<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>
</section>
<section><a class='slide_break' href='rails_database_and_model.html#slide-18'>▻</a>
<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></section>
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