How to insert data from a many to many relationship from typeorm?

Working with many-to-many relationships and inserting data in TypeORM involves several steps. I will demonstrate this process with an example.

1. Defining Entities

Assume we have two entities, User and Group, which have a many-to-many relationship. First, we need to define this relationship in both entities. In TypeORM, we can use the @ManyToMany decorator to identify this relationship and use @JoinTable to define the join table on the owning side.

typescript
import { Entity, PrimaryGeneratedColumn, Column, ManyToMany, JoinTable } from "typeorm";
import { Group } from "./Group";

@Entity()
export class User {
    @PrimaryGeneratedColumn()
    id: number;

    @Column()
    name: string;

    @ManyToMany(() => Group)
    @JoinTable()
    groups: Group[];
}

typescript
import { Entity, PrimaryGeneratedColumn, Column, ManyToMany } from "typeorm";
import { User } from "./User";

@Entity()
export class Group {
    @PrimaryGeneratedColumn()
    id: number;

    @Column()
    name: string;

    @ManyToMany(() => User)
    users: User[];
}

2. Inserting Data

When inserting data, it's important to properly handle the related entities. This typically involves the following steps:

a. Creating Entity Objects

typescript
let user = new User();
user.name = "Alice";

let group1 = new Group();
group1.name = "Group1";

let group2 = new Group();
group2.name = "Group2";

b. Setting Relationships

Before establishing the relationship, if the records are new, we may need to save these entities first.

typescript
import { createConnection, getRepository } from "typeorm";

async function main() {
    await createConnection(/*...*/);

    const userRepository = getRepository(User);
    const groupRepository = getRepository(Group);

    await groupRepository.save([group1, group2]);

    // Associate user with groups
    user.groups = [group1, group2];
    await userRepository.save(user);
}

3. Verifying Data

To verify that the data is correctly inserted, we can query existing records and check if the relationships are properly set.

typescript
async function checkUser() {
    const users = await userRepository.find({ relations: ["groups"] });
    console.log(users);
}

checkUser();

This example demonstrates how to set up many-to-many relationships and insert related data in TypeORM. In practical applications, additional scenarios may need to be handled, such as updating or deleting relationships and managing transactions.