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Inherited Binding

Field decorators are also applied to fields declared in parent classes.
This lets you define common fields once in a base class and reuse them across child classes.

Example​

class BaseRequest {
  @Body()
  @Length(10)
  id!: string
}

class CreateUserRequest extends BaseRequest {
  @Body()
  @OneOf(["admin", "user"])
  role!: string
}

Result​

CreateUserRequest will have the following fields:

  • id : inherited from BaseRequest

  • role : defined in CreateUserRequest

When you pass CreateUserRequest to bindingCargo, both the inherited id and the locally declared role are bound and validated together.

Redeclaring an Inherited Field​

Re-declaring an inherited field in a child class does not replace the parent's definition — the decorators from both classes are merged onto the same field. Re-applying a source decorator this way (for example @Body() on a field the parent already sources with @Body()) produces a schema error:

Update.id: @Body + @Body cannot be combined; pick a single source

So each field should be declared in a single class. To change how a field is bound or validated, edit it where it is originally declared rather than redeclaring it in a subclass.

Notes​

  • Fields are collected across the entire prototype chain, so multiple levels of inheritance are supported.