Difference between leftJoin and leftJoinAndSelect in TypeORM

Question

I have the following query using TypeORM on a NestJS backend with PostgreSQL:

const queryBuilder = this.usersRepository
      .createQueryBuilder('user')
      .select([
        'user.id',
        'userWallets.balance',
        'userWallets.currency',
      ])
      .leftJoin('user.userWallets', 'userWallets')

In user entity the one to many relationship with UserWallet is defined.

 @OneToMany(() => UserWallet, (userWallet) => userWallet.user)
  userWallets: UserWallet[];

And the many to one with User in user wallet entity

@ManyToOne(() => User, (user) => user.userWallets)
  user: User;

There are two wallets per user, so when I write the query as above I'm getting the expected array of userWallets but it only always has one element. If I write the query with a leftJoinAndSelect then I get the expected two elements in the userWallets array.

const queryBuilder = this.usersRepository
      .createQueryBuilder('user')
      .select([
        'user.id',
      ])
      .leftJoinAndSelect('user.userWallets', 'userWallets')

I thought that by including the user wallets field in the main select I would get them all, but there seems to be a difference and I cannot find any clarification in the TypeORM docs or elsewhere. What is the difference?

Answer 1

Maybe you need to add .getMany(), the different is if you need show properties from userWallets you have to use leftJoinAndSelect, but if you only need userWallets for example on a .where() but u doesn't need show properties from userWallets only use this entity on the .where() you could use leftJoin

const queryBuilder = this.usersRepository
      .createQueryBuilder('user')
      .leftJoinAndSelect('user.userWallets', 'userWallets')
      .select([
        'user.id',
      ])
      .getMany()

here there's an exmple

return await repository.createQueryBuilder('letra')
    .leftJoinAndSelect('letra.Comentarios', 'comentarios')
    .leftJoinAndSelect('letra.Configuraciones', 'configuraciones')
    .leftJoin('letra.Usuario', 'usuario')
    .leftJoin('letra.Cancion', 'cancion')
    .where('usuario.UsuarioId = :usuarioId AND cancion.CancionId = :cancionId', {
        usuarioId, 
        cancionId
    })
    .getManyAndCount()

I wanna show lyrics from certain user and certain song so I use leftJoin because I need in the where

.where('usuario.UsuarioId = :usuarioId AND cancion.CancionId = :cancionId', {
        usuarioId, 
        cancionId
    })

But in this example I don't wanna show the properties from user and song, what I wanna show is my lyrics and this

.leftJoinAndSelect('letra.Comentarios', 'comentarios')
.leftJoinAndSelect('letra.Configuraciones', 'configuraciones')