TypeOrm/PostgreSQL createQueryBuilder：来自连接表的 select 列

Question

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I want to select only a column from a table that I'm joining into. A separator has a facility , a facility has a customer , and I want to select customer.id by providing a separatorId .

Below is what I have tried, but this returns a Separator .

return await this.separatorRepository
  .createQueryBuilder('separator')
  .select(['customer.companyId'])
  .innerJoin('separator.facility', 'facility')
  .innerJoin('facility.customer', 'customer')
  .where('separator.id = :separatorId', { separatorId })
  .getOne();

How do I change this query to get customer.id ?

Answer 1

I suppose your joined tables are not selected from because you use innerJoin method instead of innerJoinAndSelect . Additionally, since getOne returns objects with your entity type ( Separator in your case), you need to make sure the relations between Separator , Facility , and Customer are properly specified.

Entities:

@Entity()
export class Customer {
    @PrimaryColumn()
    id: number;
}

@Entity()
export class Facility {
    @PrimaryColumn()
    id: number;

    @OneToOne(() => Customer)
    @JoinColumn()
    customer: Customer;
}

@Entity()
export class Separator {
    @PrimaryColumn()
    id: number;

    @OneToOne(() => Facility)
    @JoinColumn()
    facility: Facility;
}

Query:

return await this.separatorRepository
  .createQueryBuilder('separator')
  .innerJoinAndSelect('separator.facility', 'facility')
  .innerJoinAndSelect('facility.customer', 'customer')
  .where('separator.id = :separatorId', { separatorId })
  .getOne();

The query yields you the instance of Separator with the joined entities, so you could get your customer.id from there.