DiscriminatorValue

@tsed/schema

Usage

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

See /packages/specs/schema/src/decorators/class/discriminatorValue.ts.

Overview

function DiscriminatorValue(value?: string, ...values: string[]): ClassDecorator;

• value (string): Optional. - The discriminator value (auto-generated if omitted)

• values (string[]): - Additional alias values for this subclass

Description

Declares the discriminator value for a subclass in a polymorphic hierarchy.

The @DiscriminatorValue() decorator specifies the value that should be present in the discriminator key property to identify this specific subclass. This is used together with @DiscriminatorKey() on the base class for proper polymorphic type resolution during serialization and deserialization.

Basic Usage

abstract class Event {
  @DiscriminatorKey()
  type: string;

  @Property()
  timestamp: Date;
}

@DiscriminatorValue("page_view")
class PageView extends Event {
  @Property()
  url: string;

  @Property()
  referrer: string;
}

@DiscriminatorValue("action")
class Action extends Event {
  @Property()
  actionName: string;

  @Property()
  metadata: object;
}

Auto-Generated Values

If no value is provided, it auto-generates from the class name in snake_case:

@DiscriminatorValue()  // Generates "custom_action"
class CustomAction extends Event {
  @Property()
  customField: string;
}

Multiple Values (Aliases)

Support multiple discriminator values for the same class:

@DiscriminatorValue("click", "tap", "press")
class ClickEvent extends Event {
  // Matches when type is "click", "tap", OR "press"
}

Payment Methods Example

abstract class PaymentMethod {
  @DiscriminatorKey()
  type: string;
}

@DiscriminatorValue("credit_card")
class CreditCardPayment extends PaymentMethod {
  @Property()
  cardNumber: string;

  @Property()
  cvv: string;
}

@DiscriminatorValue("paypal")
class PayPalPayment extends PaymentMethod {
  @Property()
  email: string;
}

@DiscriminatorValue("bank_transfer")
class BankTransfer extends PaymentMethod {
  @Property()
  iban: string;
}

With API Endpoints

@Post("/events")
async trackEvent(@BodyParams() event: Event) {
  // Framework automatically deserializes to correct subclass
  // based on the 'type' field value in request body
  if (event instanceof PageView) {
    // Handle page view
  } else if (event instanceof Action) {
    // Handle action
  }
}

OpenAPI Generation

Generates proper discriminator mapping:

{
  "discriminator": {
    "propertyName": "type",
    "mapping": {
      "page_view": "#/components/schemas/PageView",
      "action": "#/components/schemas/Action"
    }
  }
}

Use Cases

• Event Systems: Different event types with shared structure
• Payment Processing: Multiple payment method types
• Notification Systems: Various notification channels
• Content Types: Polymorphic content (articles, videos, images)
• API Responses: Different response formats based on type

Important Notes

• Must be used on subclasses that extend a class with @DiscriminatorKey()
• Each subclass should have a unique discriminator value
• If omitted, value is auto-generated from class name (snake_case)
• Multiple values create aliases for backward compatibility
• Works with OpenAPI discriminator specification