typeorm/docs/sequelize-migration.md

Migration from Sequelize to TypeORM

• Setting up a connection
• Schema synchronization
• Creating a models
• Other model settings
• Working with models
• Setup associations (relations)

Setting up a connection

In sequelize you create connection this way:

const sequelize = new Sequelize("database", "username", "password", {
  host: "localhost",
  dialect: "mysql"
});

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

In TypeORM you create connection following way:

import {createConnection} from "typeorm";

createConnection({
    type: "mysql",
    host: "localhost",
    username: "username",
    password: "password"
}).then(connection => {
    console.log("Connection has been established successfully.");
})
.catch(err => {
    console.error("Unable to connect to the database:", err);
});

Then you can get your connection instance from anywhere in your app using getConnection function.

Schema synchronization

In sequelize you do schema synchronization this way:

Project.sync({force: true});
Task.sync({force: true});

In TypeORM you just add synchronize: true in the connection options:

createConnection({
    type: "mysql",
    host: "localhost",
    username: "username",
    password: "password",
    synchronize: true
});

Creating a models

This is how define models in sequelize:

module.exports = function(sequelize, DataTypes) {

    const Project = sequelize.define("project", {
      title: DataTypes.STRING,
      description: DataTypes.TEXT
    });
    
    return Project;

};

module.exports = function(sequelize, DataTypes) {

    const Task = sequelize.define("task", {
      title: DataTypes.STRING,
      description: DataTypes.TEXT,
      deadline: DataTypes.DATE
    });
    
    return Task;
};

In TypeORM such models are called entities and you can define them this way:

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";

@Entity()
export class Project {
    
    @PrimaryGeneratedColumn()
    id: number;
    
    @Column()
    title: string;
    
    @Column()
    description: string;
    
}

import {Entity, PrimaryGeneratedColumn, Column} from "typeorm";

@Entity()
export class Task {
    
    @PrimaryGeneratedColumn()
    id: number;
    
    @Column()
    title: string;
    
    @Column("text")
    description: string;
    
    @Column()
    deadline: Date;
    
}

Its highly recommended to define one entity class per file. TypeORM allows you to use your classes as database models and provides you a declarative way to define what part of your model will become part of your database table. Power of TypeScript gives you type hinting and other useful features that you can use in classes.

Other model settings

Following in sequelize:

flag: { type: Sequelize.BOOLEAN, allowNull: true, defaultValue: true },

Can be achieved this way in TypeORM:

@Column({ nullable: true, default: true })
flag: boolean;

Following in sequelize:

flag: { type: Sequelize.BOOLEAN, defaultValue: true },

Can be achieved this way in TypeORM:

@Column({ default: () => "NOW()" })
myDate: Date;

Following in sequelize:

someUnique: { type: Sequelize.STRING, unique: true },

Can be achieved this way in TypeORM:

@Column({ unique: true })
someUnique: string;

Following in sequelize:

fieldWithUnderscores: { type: Sequelize.STRING, field: 'field_with_underscores' },

Can be achieved this way in TypeORM:

@Column({ name: "field_with_underscores" })
fieldWithUnderscores: string;

Following in sequelize:

incrementMe: { type: Sequelize.INTEGER, autoIncrement: true },

Can be achieved this way in TypeORM:

@Column()
@Generated()
incrementMe: number;

Following in sequelize:

identifier: { type: Sequelize.STRING, primaryKey: true },

Can be achieved this way in TypeORM:

@Column({ primary: true })
identifier: string;

To create createDate and updateDate-like columns you need to defined two columns (named it as you want) in your entity:

@CreateDateColumn();
createDate: Date;

@UpdateDateColumn();
updateDate: Date;

Working with models

To create a new model in sequelize you do following:

const employee = await Employee.create({ name: "John Doe", title: "senior engineer" });

In TypeORM there are several ways to create a new model:

const employee = new Employee(); // you can use constructor parameters as well
employee.name = "John Doe";
employee.title = "senior engineer";

or

const employee = Employee.create({ name: "John Doe", title: "senior engineer" });

if you want to load exist entity from the database and replace some of its properties you can use following method:

const employee = await Employee.preload({ id: 1, name: "John Doe" });

To access properties in sequelize you do following:

console.log(employee.get('name'));

In TypeORM you simply do:

console.log(employee.name);

To create index in sequelize you do following:

sequelize.define("user", {}, {
  indexes: [
    {
      unique: true,
      fields: ["firstName", "lastName"]
    }
  ]
});

In TypeORM you do:

@Entity()
@Index(["firstName", "lastName"], { unique: true })
export class User {
}

Setup associations (relations)

Associations in TypeORM are called "relations".