MinItems

@tsed/schema

Usage

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

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

Overview

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

Description

Sets the minimum number of items required in an array.

The @MinItems() decorator validates that an array has at least the specified number of elements. This is useful for ensuring required data is provided, enforcing business rules, or guaranteeing minimum quantities.

Basic Usage

class OrderModel {
  @CollectionOf(String)
  @MinItems(1)
  items: string[];
  // Order must have at least 1 item
}

Generated schema:

{
  "type": "object",
  "properties": {
    "items": {
      "type": "array",
      "minItems": 1,
      "items": {
        "type": "string"
      }
    }
  }
}

With MaxItems - Range Validation

class VotingModel {
  @CollectionOf(String)
  @MinItems(3)
  @MaxItems(10)
  candidates: string[];
  // Must have between 3 and 10 candidates
}

Required Selections

class SurveyResponse {
  @CollectionOf(String)
  @MinItems(1)
  selectedOptions: string[];
  // User must select at least one option
}

Business Rules

class TeamCreation {
  @CollectionOf(String)
  @MinItems(2)
  memberIds: string[];
  // Team requires minimum 2 members
}

Validation Examples

@MinItems(2)
items: string[];

// Valid:
["a", "b"]              // 2 items (≥ 2)
["a", "b", "c"]         // 3 items (≥ 2)

// Invalid:
[]                      // 0 items (< 2)
["a"]                   // 1 item (< 2)

Use Cases

• Required Data: Ensure minimum data is provided
• Business Logic: Enforce minimum quantities (team size, votes)
• Data Quality: Prevent submission with insufficient information
• User Input: Require multiple selections or answers
• Validation: Ensure arrays are not empty when data is expected

Non-Empty Arrays

class CommentModel {
  @CollectionOf(String)
  @MinItems(1)
  tags: string[];
  // Prevent empty tag arrays
}

Combining with Uniqueness

class CategoryModel {
  @CollectionOf(String)
  @MinItems(2)
  @UniqueItems()
  subcategories: string[];
  // Must have at least 2 unique subcategories
}

Important Notes

• The value must be a non-negative integer (0 or greater)
• Throws an error if a negative value is provided
• Omitting @MinItems() is equivalent to @MinItems(0) (no minimum)
• Can be combined with custom error messages using ajv-errors
• Arrays with exactly minItems elements are valid (inclusive)

Default Behavior

Without @MinItems(), arrays can be empty:

@CollectionOf(String)
tags: string[];
// Valid: [], ["tag1"], ["tag1", "tag2"], etc.

With @MinItems(1), empty arrays are rejected:

@CollectionOf(String)
@MinItems(1)
tags: string[];
// Invalid: []
// Valid: ["tag1"], ["tag1", "tag2"], etc.