sequelize

What is sequelize?

Sequelize is a promise-based Node.js ORM (Object-Relational Mapping) library for Postgres, MySQL, MariaDB, SQLite, and Microsoft SQL Server. It features solid transaction support, relations, eager and lazy loading, read replication and more. Sequelize follows the Active Record paradigm and allows developers to define models and their relationships in a way that abstracts database access, making it easier to maintain and evolve the application codebase.

What are sequelize's main functionalities?

Model Definition

This feature allows you to define models in Sequelize, which represent tables in the database. Each model can have various attributes and their respective data types.

const User = sequelize.define('user', { username: Sequelize.STRING, birthday: Sequelize.DATE });

CRUD Operations

Sequelize provides methods for creating, reading, updating, and deleting records in the database, which correspond to the CRUD operations.

User.create({ username: 'alice', birthday: new Date(1986, 6, 20) }); User.findAll(); User.update({ username: 'alicejr' }, { where: { id: 1 } }); User.destroy({ where: { id: 1 } });

Associations

This feature allows you to define associations between models. For example, a user can have many posts, and a post belongs to a user.

User.hasMany(Post); Post.belongsTo(User);

Transactions

Sequelize supports transactions which allow you to execute multiple queries in an atomic way, ensuring data integrity.

sequelize.transaction(transaction => { return User.create({ username: 'bob' }, { transaction }); });

Migrations

Sequelize has a migration tool that allows you to define changes to the database schema, which can be applied and rolled back programmatically.

module.exports = { up: (queryInterface, Sequelize) => { return queryInterface.createTable('users', { id: { allowNull: false, autoIncrement: true, primaryKey: true, type: Sequelize.INTEGER }, username: { type: Sequelize.STRING } }); }, down: (queryInterface, Sequelize) => { return queryInterface.dropTable('users'); } };

Other packages similar to sequelize

mongoose

Mongoose is an ODM (Object Data Modeling) library for MongoDB and Node.js. It manages relationships between data, provides schema validation, and is used to translate between objects in code and the representation of those objects in MongoDB. Compared to Sequelize, Mongoose is specific to MongoDB, whereas Sequelize supports multiple SQL databases.

typeorm

TypeORM is an ORM that can run in Node.js and be used with TypeScript and JavaScript (ES5, ES6, ES7, ES8). It supports the Data Mapper pattern, unlike Sequelize which is more Active Record. TypeORM is highly influenced by other ORMs, such as Hibernate, Doctrine, and Entity Framework.

knex

Knex.js is a SQL query builder for Postgres, MSSQL, MySQL, MariaDB, SQLite3, Oracle, and Amazon Redshift, designed to be flexible, portable, and fun to use. It does not provide full ORM capabilities but allows you to build and run SQL queries in a more programmatic and database-agnostic way. It is often used with objection.js, which is an ORM built on top of Knex.

bookshelf

Bookshelf.js is a JavaScript ORM for Node.js, built on the Knex SQL query builder. It features transaction support, eager/nested-eager relation loading, and polymorphic associations. Bookshelf follows a somewhat similar pattern to Sequelize but is built on top of Knex, which gives it a different flavor in terms of query building.

README

Sequelize

MySQL, PostgresSQL, and SQLite Object Relational Mapper (ORM) for node.

Important Notes

2.0.0

There is a parallel "branch" of the project, released as 2.0.0-alphaX in NPM. All those releases are based on the master and will get all the changes of the master. However, 2.0.0 will contain backwards compatibility breaking changes. Check the changelog of the branch: https://github.com/sequelize/sequelize/blob/milestones/2.0.0/changelog.md

1.6.0

• We changed the way timestamps are handled. From v1.6.0 on timestamps are stored and loaded as UTC.
• Support for synchronous migrations has been dropped. up and down methods in migrations do have a third parameter which is the callback parameter. Pass an error or an error message as first parameter to the callback if something went wrong in the migration.

Blogposts/Changes

• v1.6.0 Eager loading, support for enums, decimals and bigint, performance improvements …
• v1.4.1: deprecation of node < 0.6, logging customization, ...
• v1.4.0: postgresql, connection pooling, ...
• v1.3.0: migrations, cross-database, validations, new listener notation, ...
• v1.2.1: changes some defaults and some interfaces
• v1.0.0: complete rewrite

Features

• Schema definition
• Schema synchronization/dropping
• Easy definition of class/instance methods
• Instance saving/updating/dropping
• Asynchronous library
• Associations
• Importing definitions from single files
• Promises

Documentation and Updates

You can find the documentation and announcements of updates on the project's website. If you want to know about latest development and releases, follow me on Twitter. Also make sure to take a look at the examples in the repository. The website will contain them soon, as well.

• Documentation
• Twitter
• IRC
• Google Groups
• XING (pretty much inactive, but you might want to name it on your profile)

Running Examples

Instructions for running samples are located in the example directory. Try these samples in a live sandbox environment:

Roadmap

A very basic roadmap. Chances aren't too bad, that not mentioned things are implemented as well. Don't panic :)

1.7.0

• Check if lodash is a proper alternative to current underscore usage.
• Transactions
• Support for update of tables without primary key
• MariaDB support
• Support for update and delete calls for whole tables without previous loading of instances Implemented in #569 thanks to @optiltude
• Eager loading of nested associations #388
• Model#delete (renamed to Model.destroy())
• Validate a model before it gets saved. Implemented in #601, thanks to @durango
• Move validation of enum attribute value to validate method
• BLOB #99
• Support for foreign keys Implemented in #595, thanks to @optilude

1.7.x

• Complete support for non-id primary keys

1.8.0

• API sugar (like Model.select().where().group().include().all())
• Schema dumping
• enum support
• attributes / values of a dao instance should be scoped

2.0.0

• save datetimes in UTC
• encapsulate attributes if a dao inside the attributes property
• add getters and setters for dao Implemented in #538, thanks to iamjochem
• add proper error message everywhere
• refactor validate() output data structure, separating field-specific errors from general model validator errors (i.e. {fields: {field1: ['field1error1']}, model: ['modelError1']} or similar)

Collaboration 2.0

I'm glad to get pull request if any functionality is missing or something is buggy. But please ... run the tests before you send me the pull request.

Still interested? Coolio! Here is how to get started:

1. Prepare your environment

Here comes a little surprise: You need Node.JS. In order to be a productive developer, I would recommend the latest v0.8. Also I usually recommend NVM.

Once Node.JS is installed on your computer, you will also have access to the lovely Node Package Manager (NPM).

2. Database... Come to me!

First class citizen of Sequelize was MySQL. Over time, Sequelize began to become compatible to SQLite and PostgreSQL. In order to provide a fully featured pull request, you would most likely want to install of them. Give it a try, it's not that hard.

If you are too lazy or just don't know how to get this work, feel free to join the IRC channel (freenode@#sequelizejs).

For MySQL and PostgreSQL you'll need to create a DB called sequelize_test. For MySQL this would look like this:

$ echo "CREATE DATABASE sequelize_test;" | mysql -uroot

CLEVER NOTE: your local MySQL install must be with username root without password. If you want to customize that just hack in the tests, but make sure to don't commit your credentials, we don't want to expose your personal data in sequelize codebase ;)

AND ONE LAST THING: Once npm install worked for you (see below), you'll get SQLite tests for free :)

3. Install the dependencies

Just "cd" into sequelize directory and run npm install, see an example below:

$ cd path/to/sequelize
$ npm install

4. Run the tests

Right now, the test base is split into the test folder (which contains the lovely Mocha tests).

As you might haven't installed all of the supported SQL dialects, here is how to run the test suites for your development environment:

$ # run all tests at once:
$ make all

$ # run the buster specs for mysql:
$ make mysql

$ # run the buster specs for sqlite:
$ make sqlite

$ # run the buster specs for postgresql:
$ make pgsql

$ # alternatively you can pass database credentials with $variables when testing
$ DIALECT=dialect SEQ_DB=database SEQ_USER=user SEQ_PW=password make test

5. That's all

Just commit and send pull requests. Happy hacking and thank you for contributing. Ah and one last thing: If you think you deserve it, feel free to add yourself to the package.json. Also I always look for projects which are using sequelize. If you have one of them, drop me a line!

6. Some words about coding style

As people are regularly complaining about missing semi-colons and strangely formatted things, I just want to explain the way I code JavaScript (including Sequelize ... obviously). I won't reject any pull-request because of having a different code style than me but it would be good to have a consistent way of coding in the whole project. Here are my rules of thumb:

• No semi-colons. Where possible I try to avoid semi-colons. Please don't discuss this topic with me. Thanks.
• Curly braces for single line if blocks. I always add curly braces to if blocks. Same for loops and other places.
• Spacing. Indentation = 2 spaces. Also I add a lot of spaces where possible. See below.
• Anonymous functions over names functions. Usually I declare a function and assign it to a variable: var foo = function() {}
• Variable declarations. If multiple variables are defined, I use a leading comma for separation.
• Camelcased variable names. No underscores.
• Make sure that key is in objects when iterating over it. See below.

6.1. Spaces

Use spaces when defining functions.

function(arg1, arg2, arg3) {
  return 1
}

Use spaces for if statements.

if (condition) {
  // do something
} else {
  // something else
}

6.2. Variable declarations

var num  = 1
  , user = new User()
  , date = new Date()

6.3. For-In-loops

for (var key in obj) {
  if (obj.hasOwnProperty(key)) {
    console.log(obj[key])
  }
}

6.4. JSHint options

{
  "globals": {
    "spyOn": false,
    "it": false,
    "console": false,
    "describe": false,
    "expect": false,
    "beforeEach": false,
    "waits": false,
    "waitsFor": false,
    "runs": false
  },
  "camelcase": true,
  "curly": true,
  "forin": true,
  "indent": 2,
  "unused": true,
  "asi": true,
  "evil": false,
  "laxcomma": true,
  "es5": true
}