How to set ForeignKey explicitly without having property for loading relations in TypeORM?

When using TypeORM for database operations, there are scenarios where you need to directly set a foreign key (Foreign Key) without loading the entire related entity object. This is common during performance optimization or when the data of the related entity is known, and only the foreign key needs to be set without requiring other field data.

In TypeORM, you can set the foreign key by directly accessing the foreign key field of the entity without loading the related entity. Each foreign key relationship typically has a corresponding column decorator (e.g., @ManyToOne), and you can set the foreign key by directly assigning the value to this column.

Example

Assume we have two entities: User and Photo. Each Photo belongs to a User, and in the Photo entity, we have a userId field as the foreign key:

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

    @OneToMany(type => Photo, photo => photo.user)
    photos: Photo[];
}

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

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

    @Column()
    userId: number;
}

In the above code, the Photo entity has a userId field as the foreign key pointing to User. If you know the user's ID and do not need to load the User entity, you can directly set userId:

typescript
async function assignPhotoToUser(photoId: number, userId: number) {
    const photoRepository = getRepository(Photo);
    let photo = new Photo();
    photo.id = photoId;
    photo.userId = userId;  // Directly set the foreign key
    await photoRepository.save(photo);
}

In this example, by setting the userId field, we establish the relationship between Photo and User without loading the User entity. This approach reduces database operation complexity and can improve application performance.

Notes

• Ensure the ID set for the foreign key exists in the database; otherwise, it may violate foreign key constraints.
• When using this method, TypeORM does not automatically handle cascading deletes or updates. If required, you must manually manage database integrity.

This method provides flexible handling of database relationships, especially valuable in scenarios involving large data volumes and performance optimization.