Extending Class Schemas

When working with OpenAPI schemas in InversifyJS HTTP, you might need to create schemas that extend from a base schema. This is useful for creating inheritance hierarchies where child schemas include all properties from a parent schema plus additional properties.

Basic Schema Extension

To extend a class schema, you can use the @OasSchema decorator with a function that takes a ToSchemaFunction parameter. This function allows you to reference other schema classes.

@OasSchema()
export class BaseSchema {
  @OasSchemaProperty({
    description: 'A common string property',
    type: 'string',
  })
  public foo!: string;
}

@OasSchema((toSchema: ToSchemaFunction) => toSchema(BaseSchema), {
  customAttributes: {
    unevaluatedProperties: false,
  },
})
export class ExtendedSchema extends BaseSchema {
  @OasSchemaProperty({
    description: 'An additional property in the extended schema',
    type: 'string',
  })
  public bar!: string;

  @OasSchemaProperty({
    description: 'A numeric property in the extended schema',
    minimum: 0,
    type: 'number',
  })
  public count!: number;
}

How It Works

1. Base Schema: The BaseSchema class is decorated with @OasSchema and includes the foo property decorated with @OasSchemaProperty.

2. Extended Schema: The ExtendedSchema class:

   • Extends BaseSchema using TypeScript inheritance (extends BaseSchema)
   • Uses @OasSchema((toSchema: ToSchemaFunction) => toSchema(BaseSchema)) to reference the base schema in the OpenAPI specification
   • Adds additional properties (bar and count) with their own @OasSchemaProperty decorators

3. OpenAPI Generation: This generates an OpenAPI schema where:

   • The base schema is defined with its properties
   • The extended schema uses allOf with a reference ($ref) to the base schema
   • The extended schema includes its own properties in addition to the inherited ones