Default

@tsed/schema

Usage

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

See /packages/specs/schema/src/decorators/common/default.ts.

Overview

function Default(defaultValue: JSONSchema7Type | undefined | (() => JSONSchema7Type)): (...args: any[]) => any;

• defaultValue (JSONSchema7Type | undefined | (() => JSONSchema7Type)): - The default value (or function returning the value)

Description

Specifies a default value for a property in the JSON Schema.

The @Default() decorator sets the default value that should be used when a property is not provided in the input. This is primarily used for documentation in OpenAPI specs and can be used by validation libraries that support default value insertion.

Basic Usage

class UserModel {
  @Default("guest")
  role: string = "guest";

  @Default(0)
  loginCount: number = 0;

  @Default(true)
  active: boolean = true;
}

Generated schema:

{
  "type": "object",
  "properties": {
    "role": {
      "type": "string",
      "default": "guest"
    },
    "loginCount": {
      "type": "integer",
      "default": 0
    },
    "active": {
      "type": "boolean",
      "default": true
    }
  }
}

With Objects

class ConfigModel {
  @Default({ theme: "light", lang: "en" })
  preferences: object = { theme: "light", lang: "en" };
}

With Arrays

class ListModel {
  @Default([])
  items: string[] = [];
}

Dynamic Defaults with Functions

class TimestampModel {
  @Default(() => new Date().toISOString())
  createdAt: string;
  // Default value computed at schema generation time
}

Use Cases

• Optional Configuration: Provide sensible defaults for config properties
• API Documentation: Show default values in OpenAPI/Swagger docs
• Form Generation: Pre-populate form fields with default values
• Database Models: Document default column values

Important Notes

• The decorator adds default info to the schema but doesn't set TypeScript property initializers
• Recommended to match TypeScript initializer with decorator value for consistency
• Default value should be valid according to the property's schema
• Not all validation libraries automatically apply defaults

With Validation

class PaginationParams {
  @Default(10)
  @Minimum(1)
  @Maximum(100)
  limit: number = 10;

  @Default(0)
  @Minimum(0)
  offset: number = 0;
}