MaxProperties

@tsed/schema

Usage

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

See /packages/specs/schema/src/decorators/collections/maxProperties.ts.

Overview

const MaxProperties: import("../../utils/withErrorMsg.js").ErrorChainedDecorator<(maxProperties: number) => (...args: any[]) => any>;

Description

Sets the maximum number of properties allowed on an object.

The @MaxProperties() decorator validates that an object has at most the specified number of properties. This is useful for limiting dynamic object sizes, preventing excessive data structures, or enforcing schema constraints on flexible objects.

On Property

class ConfigModel {
  @MaxProperties(5)
  metadata: Record<string, any>;
  // Object can have at most 5 properties
}

Generated schema:

{
  "type": "object",
  "properties": {
    "metadata": {
      "type": "object",
      "maxProperties": 5
    }
  }
}

On Class

@MaxProperties(10)
class DynamicModel {
  // Class instances can have at most 10 properties total
}

Generated schema:

{
  "type": "object",
  "maxProperties": 10
}

On Parameter

@Controller("/api")
class ApiController {
  @Post("/config")
  updateConfig(
    @BodyParams() @MaxProperties(10) config: any
  ) {
    // Config object limited to 10 properties
  }
}

With MinProperties - Range Validation

class FilterModel {
  @MinProperties(1)
  @MaxProperties(5)
  filters: Record<string, string>;
  // Must have 1-5 filter properties
}

Dynamic Objects

class UserPreferences {
  @MaxProperties(20)
  @AdditionalProperties({ type: "string" })
  settings: Record<string, string>;
  // Up to 20 custom settings, all string values
}

Validation Examples

@MaxProperties(2)
data: object;

// Valid:
{}                         // 0 properties (≤ 2)
{ a: 1 }                   // 1 property (≤ 2)
{ a: 1, b: 2 }             // 2 properties (≤ 2)

// Invalid:
{ a: 1, b: 2, c: 3 }       // 3 properties (> 2)

Use Cases

• API Rate Limiting: Restrict filter/query parameter counts
• Performance: Prevent overly complex objects
• Schema Constraints: Limit dynamic data structures
• Configuration: Cap number of custom settings
• Security: Prevent payload bloat attacks

Flexible Schemas

class ExtensibleModel {
  @Property()
  id: string;

  @Property()
  name: string;

  @MaxProperties(5)
  @AdditionalProperties(true)
  // 2 defined properties + up to 3 additional properties
}

Important Notes

• The value must be a non-negative integer (0 or greater)
• Throws an error if a negative value is provided
• Empty objects ({}) always pass maxProperties validation
• Counts all properties, including inherited and additional ones
• Can be combined with custom error messages using ajv-errors