docs/articles/modeling/object-inheritance.md

Object Inheritance

What

• A model contains common resuable information that can be referenced in your endpoint definitions or other models in your API design.
• When a model derives its properties from another model, the event is called inheritance.
• The model which contains the common set of properties and fields becomes a parent to other models, and it is called the base type.
• The model which inherits the common set of properties and fields is known as the derived type.
• If a base type inherits its properties from another model, the derived type automatically inherits the same properties indicating that inheritance is transitive.
• OpenAPI Specification v2 uses the allOf syntax to declare inheritance.
• allOf obtains a collection of object definitions validated independently but, collectively make up a single object.

Why

• Inheritance makes your API design more compact. It helps avoid duplication of common properties and fields.

Best Practices

Avoid using contradictory declarations such as declaring properties with the samer name but dissimilar data type in your base model and derived model.

Example

{
  Vehicle: 
    type: object
    properties: 
      brand: 
        type: string 
  Sedan: 
    allOf: # (This keyword combines the Vehicle model and the Sedan model) 
      $ref: '#/definitions/Vehicle'
      type: object
      properties: 
        isNew:
          type: boolean
}