Discriminator

@tsed/schema

Usage

import { Discriminator } from "@tsed/schema";

See /packages/specs/schema/src/domain/JsonDiscriminator.ts.

Overview

class Discriminator {
    propertyName: string;
    base: Type<any>;
    values: Map<string, Type>;
    types: Map<Type, string[]>;
    constructor({ base, propertyName, types, values }?: Partial<{
        base: Type<any>;
        propertyName: string;
        values: Map<string, Type<any>>;
        types: Map<Type, string[]>;
    }>);
    add(type: Type<string>, values: string[]): this;
    getType(discriminatorValue: string): Type<any>;
    getValues(type: Type): string[] | undefined;
    getDefaultValue(type: Type<any>): string | undefined;
    children(): Type<any>[];
}

Description

Manages discriminator mappings for polymorphic type resolution.

A discriminator enables polymorphism in schemas by using a specific property value to determine which subtype schema to apply. This is essential for inheritance hierarchies and union types in OpenAPI specifications.

Concept

When a base class has multiple derived classes, the discriminator property (e.g., "type", "kind") indicates which concrete class an object represents.

Usage

// Base class
@DiscriminatorKey("type")
abstract class Animal {
  type: string;
}

// Derived classes
@DiscriminatorValue("dog")
class Dog extends Animal {
  breed: string;
}

@DiscriminatorValue("cat")
class Cat extends Animal {
  indoor: boolean;
}

OpenAPI Mapping

Generates OpenAPI discriminator objects:

{
  "discriminator": {
    "propertyName": "type",
    "mapping": {
      "dog": "#/components/schemas/Dog",
      "cat": "#/components/schemas/Cat"
    }
  }
}

Key Features

• Type Mapping: Maps discriminator values to TypeScript classes
• Bidirectional Lookup: Find type by value or values by type
• Default Values: Get the default discriminator value for a type
• Children Discovery: List all derived types

propertyName

propertyName: string;

base

base: Type<any>;

values

values: Map<string, Type>;

types

types: Map<Type, string[]>;

add

add(type: Type<string>, values: string[]): this;

getType

getType(discriminatorValue: string): Type<any>;

getValues

getValues(type: Type): string[] | undefined;

getDefaultValue

getDefaultValue(type: Type<any>): string | undefined;

children

children(): Type<any>[];