Allow

@tsed/schema

Usage

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

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

Overview

function Allow(...values: any[]): any;

• values (any[]): - Values to allow even when the field is required (can include a model class)

Description

Adds specific values to the list of allowed values for required properties or parameters.

When a property or parameter is marked as required, it typically rejects null, undefined, and empty strings. The @Allow() decorator lets you explicitly permit certain values that would otherwise fail required validation.

Common Use Case: Allow Empty Strings

By default, required fields reject empty strings. Use @Allow("") to permit them:

class UserModel {
  @Required()
  @Allow("")  // Empty string is now valid even though field is required
  nickname: string;
}

On Method Parameters

@Post("/")
async createUser(
  @Allow("")
  @BodyParams("nickname")
  nickname: string  // Empty string allowed, but null/undefined still rejected
) {
  // nickname can be "" but not null/undefined
}

Multiple Allowed Values

class ConfigModel {
  @Required()
  @Allow(null, "", 0)  // Allow null, empty string, or zero
  threshold: number | null;
}

Combining with Type Specification

You can specify a model type along with allowed values:

class FormData {
  @Allow("", SomeModel)  // Allow empty string or a SomeModel instance
  data: SomeModel;
}

Behavior

• For parameters: Automatically marks the parameter as required
• For properties: Automatically adds the property to the required list
• Adds specified values to the schema's allowedRequiredValues list

Validation Logic

Required validation will pass if the value is:

• Not null, undefined, or "" (default required behavior)
• OR one of the values specified in @Allow()