Can I have a polymorphic response in Nestjs OpenAPI? - nestjs

Question

Using Nestjs OpenAPI module, I can specify the response type using a decorator like so:
#Controller('app')
class MyController {
#Get()
#ApiResponse({ status: 200, description: 'Success', type: MyDto })
getThing() {
// code here
}
}
However, the documentation does not specify how to have a polymorphic response type (or in OpenAPI terms a oneOf response type). E.g., in the example below I would want to have my response type be oneOf: [MyDto, MyOtherDto]:
#Controller('app')
class MyController {
#Get()
#ApiResponse({ status: 200, description: 'Success', type: MyDto }) // What do do for type here?
getThing(): MyDto | MyOtherDto {
// code here
}
}
How can I do this?

Answer 1

Okay, so not sure if this is the best/easiest way, but a "raw schema definition" can be supplied for the #ApiResponse() decorator, like so:
#Controller('app')
class MyController {
#Get()
#ApiResponse({
status: 200,
description: 'Success',
schema: {
oneOf: [
{ $ref: getSchemaPath(MyDto) },
{ $ref: getSchemaPath(MyOtherDto) },
]
}
})
getThing(): MyDto | MyOtherDto {
// code here
}
}

Answer 2

In case your polymorphic class has a discriminator - you can take it one step further with the following code:
enum DtoType {
MY_DTO = 'MY_DTO',
MY_OTHER_DTO = 'MY_OTHER_DTO',
}
#Controller('app')
class MyController {
#Get()
#ApiResponse({
status: 200,
description: 'Success',
schema: {
oneOf: [
{ $ref: getSchemaPath(MyDto) },
{ $ref: getSchemaPath(MyOtherDto) }
],
discriminator: {
propertyName: 'type',
mapping: {
[DtoType.MY_DTO]: 'MyDto',
[DtoType.MY_OTHER_DTO]: 'MyOtherDto',
},
},
}
})
getThing(): MyDto | MyOtherDto {
// code here
}
}