Sequelize

Recall

Sequelize, like Active Record in Rails, is an ORM. ORM or Object Relation Mapping, acts an interface between the objects and the database.

Sequelize

Sequelize is a promise-based Node.js ORM for Postgres, MySQL, MariaDB, SQLite and Microsoft SQL Server.

To install:

npm install sequelize

You'll also have to manually install the driver for your database of choice:

One of the following:

$ npm install --save pg pg-hstore # Postgres
$ npm install --save mysql2
$ npm install --save mariadb
$ npm install --save sqlite3
$ npm install --save tedious # Microsoft SQL Server

In this case, we will utilize the driver for PostgreSQL:

npm install pg pg-hstore # Postgres

Sequelize CLI

npm install --save-dev sequelize-cli

Usage - For Reference

Sequelize CLI [Node: 10.15.0, CLI: 5.5.0, ORM: 5.11.0]

npx sequelize [command]

Commands:

Command	What it does	Aliases
sequelize db:migrate	Run pending migrations
sequelize db:migrate:schema:timestamps:add	Update migration table to have timestamps
sequelize db:migrate:status	List the status of all migrations
sequelize db:migrate:undo	Reverts a migration
sequelize db:migrate:undo:all	Revert all migrations ran
sequelize db:seed	Run specified seeder
sequelize db:seed:undo	Deletes data from the database
sequelize db:seed:all	Run every seeder
sequelize db:seed:undo:all	Deletes data from the database
sequelize db:create	Create database specified by configuration
sequelize db:drop	Drop database specified by configuration
sequelize init	Initializes project
sequelize init:config	Initializes configuration
sequelize init:migrations	Initializes migrations
sequelize init:models	Initializes models
sequelize init:seeders	Initializes seeders
sequelize migration:generate	Generates a new migration file	[aliases: migration:create]
sequelize model:generate	Generates a model and its migration	[aliases: model:create]
sequelize seed:generate	Generates a new seed file	[aliases: seed:create]

Setting up a connection

There are two options:

Passing connection parameters to a Sequelize constructor
Passing a single connection URI

const Sequelize = require('sequelize');

// Option 1: Passing parameters separately
const sequelize = new Sequelize('database', 'username', 'password', {
  host: 'localhost',
  dialect: /* one of 'mysql' | 'mariadb' | 'postgres' | 'mssql' */
});

// Option 2: Passing a connection URI
const sequelize = new Sequelize('postgres://user:pass@example.com:5432/dbname');

Testing Connection

We use the authenticate() function to verify the connection is OK

sequelize
  .authenticate()
  .then(() => {
    console.log('Connection has been established successfully.');
  })
  .catch(err => {
    console.error('Unable to connect to the database:', err);
  });

Closing a connection

Sequelize will keep the connection open by default, and use the same connection for all queries. If you need to close the connection, call sequelize.close() (which is asynchronous and returns a Promise).

Creating a model

Again, there are two ways to to define a model with Sequelize:

Sequelize.Model.init(attributes, options):
sequelize.define

Using method 1:

const Model = Sequelize.Model;
class User extends Model {}
User.init({
  // attributes
  firstName: {
    type: Sequelize.STRING,
    allowNull: false
  },
  lastName: {
    type: Sequelize.STRING
    // allowNull defaults to true
  }
}, {
  sequelize,
  modelName: 'user'
  // options
});

Using method 2:

const User = sequelize.define('user', {
  // attributes
  firstName: {
    type: Sequelize.STRING,
    allowNull: false
  },
  lastName: {
    type: Sequelize.STRING
    // allowNull defaults to true
  }
}, {
  // options
});

Important: The above code tells Sequelize to expect a table named users in the database with the fields firstName and lastName.

The table name is automatically pluralized by default.

Sequelize also defines by default the fields id (primary key), createdAt and updatedAt to every model.

Model Usage

Full list

Finder methods are intended to query data from the database. They do not return plain objects but instead return model instances.

.find

// search for known ids
Project.findByPk(123).then(project => {
  // project will be an instance of Project and stores the content of the table entry
  // with id 123. if such an entry is not defined you will get null
})

// search for attributes
Project.findOne({ where: {title: 'aProject'} }).then(project => {
  // project will be the first entry of the Projects table with the title 'aProject' || null
})

Sync with Database

If you want Sequelize to automatically create the table (or modify it as needed) according to your model definition, you can use the sync method, as follows:

// Note: using `force: true` will drop the table if it already exists
User.sync({ force: true }).then(() => {
  // Now the `users` table in the database corresponds to the model definition
  return User.create({
    firstName: 'John',
    lastName: 'Hancock'
  });
});

Note: If you want to avoid calling .sync() for every model, you can also call sequelize.sync() which will sync all models.

Querying

// Find all users
User.findAll().then(users => {
  console.log("All users:", JSON.stringify(users, null, 4));
});

// Create a new user
User.create({ firstName: "Jane", lastName: "Doe" }).then(jane => {
  console.log("Jane's auto-generated ID:", jane.id);
});

// Delete everyone named "Jane"
User.destroy({
  where: {
    firstName: "Jane"
  }
}).then(() => {
  console.log("Done");
});

// Change everyone without a last name to "Doe"
User.update({ lastName: "Doe" }, {
  where: {
    lastName: null
  }
}).then(() => {
  console.log("Done");
});

For a full list of querying: visit Querying Docs

Associations

BelongsTo
HasOne
HasMany
BelongsToMany

Foreign Keys

class Task extends Model {}
Task.init({ title: Sequelize.STRING }, { sequelize, modelName: 'task' });


class User extends Model {}
User.init({ username: Sequelize.STRING }, { sequelize, modelName: 'user' });


User.hasMany(Task); // Will add userId to Task model
Task.belongsTo(User); // Will also add userId to Task model

The above code will generate the following SQL:

CREATE TABLE IF NOT EXISTS "users" (
  "id" SERIAL,
  "username" VARCHAR(255),
  "createdAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "updatedAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  PRIMARY KEY ("id")
);

CREATE TABLE IF NOT EXISTS "tasks" (
  "id" SERIAL,
  "title" VARCHAR(255),
  "createdAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "updatedAt" TIMESTAMP WITH TIME ZONE NOT NULL,
  "userId" INTEGER REFERENCES "users" ("id") ON DELETE
  SET
    NULL ON UPDATE CASCADE,
    PRIMARY KEY ("id")
);

Create a CRUD API with Node, Express, & Sequelize

NPM Installs

npm install sequelize sequelize-cli pg pg-hstore

sequelize: npm library
sequelize-cli: allows us to interact with DB through sequelize
pg: postgresql client for Node.js
pg-hstore: node package for seralizing and deserializing JSON data

Create Connection

This part will be unique to your database parameters:

// takes in database name, username, password
const sequelize = new Sequelize('class_demo', 'postgres', 'postgres', {
  host: 'localhost',
  dialect: "postgres"
});
sequelize.authenticate().then(() => {
  console.log("Success!");
}).catch((err) => {
  console.log(err);
});

To test database, run nodemon and see if you see a Success message.

Create Config

touch .sequelizerc

.sequelizerc

const path = require('path')

module.exports = {
  config: path.resolve('./database/config', 'config.json'),
  'models-path': path.resolve('./database/models'),
  'seeders-path': path.resolve('./database/seeders'),
  'migrations-path': path.resolve('./database/migrations'),
}

Sequelize uses the .sequelizerc file to generate the config and the model using the specified path.

config/config.json

This part will be different depending on your DB instance.

{
  "development": {
    "username": "postgres",
    "password": "postgres",
    "database": "class_demo",
    "host": "127.0.0.1",
    "dialect": "postgres"
  },
  "test": {
    "username": "postgres",
    "password": "postgres",
    "database": "class_demo",
    "host": "127.0.0.1",
    "dialect": "postgres"
  },
  "production": {
    "username": "postgres",
    "password": "postgres",
    "database": "class_demo",
    "host": "127.0.0.1",
    "dialect": "postgres"
  }
}

Initialize

npx sequelize init

This will generate a folder structure like the one below:

Create Models and Migrations

We are going to create the following models:

User
Post
Comment

npx sequelize model:generate --name User --attributes name:string,email:string

npx sequelize model:generate --name Post --attributes title:string,content:text,userId:integer

npx sequelize model:generate --name Comment --attributes postId:integer,comment:text,userId:integer

Each of the above commands will generate a migration in: /database/migrations and a model in /database/models

We observe the folllowing migrations:

Edit Migrations

We are going to modify the migrations for Post and Comment, specifically by setting allowNull to false.

postId: {
  type: Sequelize.INTEGER,
  allowNull: false
},
comment: {
  type: Sequelize.TEXT
},
userId: {
  type: Sequelize.INTEGER,
  allowNull: false
},

Add index.js to Models

In models/index.js add the following:

const fs = require('fs');
const path = require('path');
const Sequelize = require('sequelize');
const envConfigs =  require('../config/config');

const basename = path.basename(__filename);
const env = process.env.NODE_ENV || 'development';
const config = envConfigs[env];
const db = {};

let sequelize;
if (config.url) {
  sequelize = new Sequelize(config.url, config);
} else {
  sequelize = new Sequelize(config.database, config.username, config.password, config);
}

fs
  .readdirSync(__dirname)
  .filter(file => {
    return (file.indexOf('.') !== 0) && (file !== basename) && (file.slice(-3) === '.js');
  })
  .forEach(file => {
    const model = sequelize['import'](path.join(__dirname, file));
    db[model.name] = model;
  });

Object.keys(db).forEach(modelName => {
  if (db[modelName].associate) {
    db[modelName].associate(db);
  }
});

db.sequelize = sequelize;
db.Sequelize = Sequelize;

module.exports = db;

Define Model Relationships

We will define the following:

A User has many posts
A Post belongs to a user
A Post has many comments
A Comment belongs to a post

Editing the models files:

/database/models/user.js

module.exports = (sequelize, DataTypes) => {
  const User = sequelize.define('User', {
    name: DataTypes.STRING,
    email: DataTypes.STRING
  }, {});
  User.associate = function(models) {
    // associations can be defined here
    User.hasMany(models.Post, {
      foreignKey: 'userId',
      as: 'posts',
      onDelete: 'CASCADE',
    });
    
    User.hasMany(models.Comment, {
      foreignKey: 'userId',
      as: 'comments',
      onDelete: 'CASCADE',
    });
  };
  return User;
};

/database/models/post.js

module.exports = (sequelize, DataTypes) => {
  const Post = sequelize.define('Post', {
    title: DataTypes.STRING,
    content: DataTypes.TEXT,
    userId: DataTypes.INTEGER
  }, {});
  Post.associate = function(models) {
    // associations can be defined here
    Post.hasMany(models.Comment, {
      foreignKey: 'postId',
      as: 'comments',
      onDelete: 'CASCADE',
    });

    Post.belongsTo(models.User, {
      foreignKey: 'userId',
      as: 'author',
      onDelete: 'CASCADE',
    })
  };
  return Post;
};

/database/models/comment.js

module.exports = (sequelize, DataTypes) => {
  const Comment = sequelize.define('Comment', {
    postId: DataTypes.INTEGER,
    comment: DataTypes.TEXT,
    userId: DataTypes.INTEGER
  }, {});
  Comment.associate = function(models) {
    // associations can be defined here
    Comment.belongsTo(models.User, {
      foreignKey: 'userId',
      as: 'author'
    });
    Comment.belongsTo(models.Post, {
      foreignKey: 'postId',
      as: 'post'
    });
  };
  return Comment;
};

Run Migrations

To execute the migration files, run: npx sequelize db:migrate

Seed Data

In order to populate the data with sample data, we want to run the following commands for each model:

npx sequelize seed:generate --name User

npx sequelize seed:generate --name Post

npx sequelize seed:generate --name Comment

You should see confirmation like the below figure:

Editing Seed Files

In our /seeders/ folder, we edit our seed files for each model.

/seeders/...Comment.js

module.exports = {
  up: (queryInterface, Sequelize) =>
    queryInterface.bulkInsert(
      "Comments",
      [
        {
          userId: 1,
          postId: 2,
          comment:
            "Nulla mollis molestie lorem. Quisque ut erat. Curabitur gravida nisi at nibh.",
          createdAt: new Date(),
          updatedAt: new Date()
        },
        {
          userId: 2,
          postId: 1,
          comment:
            "Maecenas tincidunt lacus at velit. Vivamus vel nulla eget eros elementum pellentesque. Quisque porta volutpat erat.",
          createdAt: new Date(),
          updatedAt: new Date()
        }
      ],
      {}
    ),

  down: (queryInterface, Sequelize) =>
    queryInterface.bulkDelete("Comments", null, {})
};

/seeders/....Post.js

module.exports = {
  up: (queryInterface, Sequelize) =>
    queryInterface.bulkInsert(
      "Posts",
      [
        {
          userId: 1,
          title: "hispotan de nu",
          content:
            "Nulla mollis molestie lorem. Quisque ut erat. Curabitur gravida nisi at nibh.",
          createdAt: new Date(),
          updatedAt: new Date()
        },
        { 
          userId: 2,
          title: 'some dummy title',
          content:
            "Maecenas tincidunt lacus at velit. Vivamus vel nulla eget eros elementum pellentesque. Quisque porta volutpat erat.",
          createdAt: new Date(),
          updatedAt: new Date()
        }
      ],

      {}
    ),

  down: (queryInterface, Sequelize) =>
    queryInterface.bulkDelete("Posts", null, {})
};

/seeders/....User.js

module.exports = {
  up: (queryInterface, Sequelize) => queryInterface.bulkInsert(
    'Users',
    [
      {
        name: 'Jane Doe',
        email: 'janedoe@example.com',
        createdAt: new Date(),
        updatedAt: new Date(),
      },
      {
        name: 'Jon Doe',
        email: 'jondoe@example.com',
        createdAt: new Date(),
        updatedAt: new Date(),
      },
    ],
    {},
  ),

  down: (queryInterface, Sequelize) => queryInterface.bulkDelete('Users', null, {}),
};

To execute the seeds, run the following command: npx sequelize db:seed:all

CRUD

Create

router.post('/', async (req, res) => {
  try {
    const post = await models.Post.create(req.body);
    return res.send(post)
  } 
  catch (error) {
    return res.status(500).send(error)
  }
})

Read

router.get('/', async (req, res) => {
  try {
    const posts = await models.Post.findAll({
      include: [
        {
          model: models.Comment,
          as: 'comments'
        },
        {
          model: models.User,
          as: 'author'
        }
      ]
    });
    return res.send(posts)
  } 
  catch (error) {
    return res.status(500).send(error)
  }
})

Update (By Id)

router.patch('/:id', async (req, res) => {
  try {
    const id = req.params.id;
    const updated = await models.Post.update(req.body, 
      {
        where: { id: id }
      });

    if (updated) {
      const updatedPost = await models.Post.findOne({ where: { id: id } });
      return res.status(200).send(updatedPost)
    }
    else {
      throw new Error('Post not found');
    }
  } 
  catch (error) {
    return res.status(500).send(error.message);
  }
})

Delete (By Id)

router.delete('/:id', async (req, res) => {
  try {
    const id = req.params.id;
    const deleted = await models.Post.destroy(
      {
        where: { id: id }
      });
      
    if (deleted) {
      return res.send("Post deleted");
    }
    else {
      throw new Error("Post not found");
    }
    
  } catch (error) {
    return res.status(500).send(error.message);
  }
})

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Sequelize

Recall

Sequelize

One of the following:

Sequelize CLI

Usage - For Reference

Setting up a connection

Testing Connection

Closing a connection

Creating a model

Model Usage

.find

Sync with Database

Querying

Associations

Foreign Keys

Create a CRUD API with Node, Express, & Sequelize

Create Connection

Create Config

config/config.json

Initialize

Create Models and Migrations

Edit Migrations

Add index.js to Models

Define Model Relationships

Run Migrations

Seed Data

Editing Seed Files

CRUD

Create

Read

Update (By Id)

Delete (By Id)

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Sequelize

Recall

Sequelize

One of the following:

Sequelize CLI

Usage - For Reference

Setting up a connection

Testing Connection

Closing a connection

Creating a model

Model Usage

.find

Sync with Database

Querying

Associations

Foreign Keys

Create a CRUD API with Node, Express, & Sequelize

Create Connection

Create Config

config/config.json

Initialize

Create Models and Migrations

Edit Migrations

Add index.js to Models

Define Model Relationships

Run Migrations

Seed Data

Editing Seed Files

CRUD

Create

Read

Update (By Id)

Delete (By Id)