MikroORM - Conditional join without foreign key constraints on the ID

I came across a rather peculiar database schema that includes a jsonb field with userId and userType attributes, along with two different user tables for distinct user types. The selection of the table to join based on the userType is crucial.

Although I can utilize a query builder to construct the necessary SQL queries, my system involves dynamically transforming GQL into Mikro filters, making manual assembly quite complex.

Is there a feasible method to achieve something akin to

@Entity()
class Job {
  @Property({ type: 'jsonb' })
  props: unknown

  @Formula(alias => `select user.name, user.dob, user.etc from user where user.id = ${alias.props->>userId`)
  user: User
}

or a similar approach? Essentially, using decorators to specify how to fetch specific data components.

typescriptmikro-orm

Answer №1

If you want to create a virtual relationship, consider using the relation decorator along with the formula option instead of directly using the @Formula decorator.

Below is an example of how you can achieve this:

@ManyToOne({
  entity: () => User,
  formula: alias => `${alias}.props->>userId`,
})
user: User

You can also refer to a working example that demonstrates something similar in the ORM tests:

https://github.com/mikro-orm/mikro-orm/blob/master/tests/issues/GH4759.test.ts#L34

Furthermore, here's an approach to handle different types using decorators:

@ManyToOne({
  entity: () => User,
  formula: alias => `case when ${alias}.userType = 'manager' then null else ${alias}.props->>userId end`,
  hidden: true,
  nullable: true,
})
user?: User;

@ManyToOne({
  entity: () => ManagerUser,
  formula: alias => `case when ${alias}.userType = 'manager' then ${alias}.props->>userId else null end`,
  hidden: true,
  nullable: true,
})
manager?: ManagerUser;

@Property({
  persist: false,
})
get userOrManager(): User | ManagerUser | undefined {
  return this.userType === 'manager' ? this.manager : this.user; 
}

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