How can I validate request body if it's a union type?

[gtamas]

I have this situation:

class A {
// some validators
}

class B {
// some validators
}

And in controller:

someMethod(
    @Param('id') id: string,
    @Body() params: A | B,
  ): Promise<SomeResult>

This doesn't work. None of the class validators get executed, I guess that's because the body is not a class, but a union of classes.

Is there any way to make this work? I want the body to be validated either as class A or B.

[icazemier]

Hi @gtamas

You should consider to implement polymorphism

An example

// Preparations

export enum MyType {
  TYPE_A = 'type-a',
  TYPE_B = 'type-b'
}

class A {
  myType: MyType.TYPE_A

 // And more stuff you need
}

class B {
  myType: MyType.TYPE_B,

 // And more stuff you need
}


class MyBody {

  @Type(
    (opts) => {
      switch (opts?.object.myType) {
        case MyType.TYPE_A:
          return A
        case MyType.TYPE_B:
          return B
        default:
          return Object
      }
    },
    {
      keepDiscriminatorProperty: true,
      discriminator: {
        property: 'myType',
        subTypes: [{ value: A, name: MyType.TYPE_A },{ value: B, name: MyType.TYPE_A }]
      }
    }
  )
  @ValidateNested()
  realBody: A | B
}

// Implementation
someMethod(
    @Param('id') id: string,
    @Body() params: MyBody,
  ): Promise<SomeResult>