LanguageExistRule

The LanguageExistRule validates that a given language ID exists and matches the expected locale.

Namespace

JobMetric\Language\Rules\LanguageExistRule

Overview

This rule ensures that:

• Language ID exists in the languages table
• Language matches the expected locale
• Can optionally allow zero (0) to bypass validation

Usage

use JobMetric\Language\Rules\LanguageExistRule;

$request->validate([
    'language_id' => ['required', new LanguageExistRule('fa')],
]);

// Disallow zero
$request->validate([
    'language_id' => ['required', new LanguageExistRule('en', false)],
]);

Parameters

• $locale (string): Two-letter lowercase locale (e.g., 'fa', 'en')
• $allowZero (bool): Whether to allow 0 to bypass validation (default: true)

Behavior

• Skips null/empty values (let 'required' handle them)
• Allows 0 if $allowZero is true
• Validates that ID exists with the given locale
• Works with both string and integer values

When to Use LanguageExistRule

Primary Use Cases

1. Foreign Key Validation in Related Models

When: You have models that reference languages via language_id foreign key.

Why:

• Ensures the language actually exists
• Validates the language matches expected locale
• Prevents orphaned records
• Maintains referential integrity

Example:

// app/Models/Post.php - Post has a language_id
// app/Http/Requests/StorePostRequest.php
use JobMetric\Language\Rules\LanguageExistRule;

public function rules(): array
{
    return [
        'title' => 'required|string',
        'content' => 'required|string',
        'language_id' => ['required', 'integer', new LanguageExistRule('fa')],
    ];
}

Real-World Scenario: Blog post creation form. User selects language - rule ensures the selected language exists and is Persian (fa).

2. User Language Preference

When: Users can set their preferred language in their profile.

Why: Ensures the selected language exists in the system.

Example:

// app/Http/Requests/UpdateUserProfileRequest.php
use JobMetric\Language\Rules\LanguageExistRule;

public function rules(): array
{
    return [
        'name' => 'required|string',
        'preferred_language_id' => [
            'nullable',
            'integer',
            new LanguageExistRule(app()->getLocale(), false) // Don't allow 0
        ],
    ];
}

Real-World Scenario: User settings page where user can change their preferred language. Rule validates the selection.

3. Content Localization

When: Creating/updating content that must be associated with a specific language.

Why: Ensures content is linked to a valid, active language.

Example:

// app/Http/Requests/StoreProductRequest.php
use JobMetric\Language\Rules\LanguageExistRule;

public function rules(): array
{
    return [
        'name' => 'required|string',
        'description' => 'required|string',
        'language_id' => [
            'required',
            'integer',
            new LanguageExistRule('en') // Must be English
        ],
    ];
}

Real-World Scenario: E-commerce product creation. Products must be in English - rule enforces this.

4. Multi-Language Content Management

When: Managing translations where each translation must reference a valid language.

Why: Prevents creating translations for non-existent languages.

Example:

// app/Http/Requests/StoreTranslationRequest.php
use JobMetric\Language\Rules\LanguageExistRule;

public function rules(): array
{
    $locale = $this->input('locale', app()->getLocale());
    
    return [
        'key' => 'required|string',
        'value' => 'required|string',
        'language_id' => [
            'required',
            'integer',
            new LanguageExistRule($locale)
        ],
    ];
}

Real-World Scenario: Translation management system. Each translation must reference a valid language matching the locale.

5. Optional Language Selection

When: Language selection is optional (can be null or 0).

Why: The allowZero parameter allows 0 to bypass validation for optional fields.

Example:

// app/Http/Requests/StoreCategoryRequest.php
use JobMetric\Language\Rules\LanguageExistRule;

public function rules(): array
{
    return [
        'name' => 'required|string',
        'language_id' => [
            'nullable',
            'integer',
            new LanguageExistRule('en', true) // Allow 0 for "no language"
        ],
    ];
}

Real-World Scenario: Category creation where language is optional. Rule allows 0 (no language) or validates existing language.

When NOT to Use

• Direct Model Queries: Don't use for checking existence in code - use Language::find() instead
• API Responses: Not needed when returning language data
• Display Logic: Don't use for showing language information
• Locale Validation: Use CheckLocaleRule for locale format validation, not this rule

Decision Tree

Do you need to validate a language_id input?
├─ Yes → Is the language_id required?
│  ├─ Yes → Use LanguageExistRule($locale, false) // Don't allow 0
│  └─ No → Use LanguageExistRule($locale, true) // Allow 0
└─ No → Don't use this rule

Common Mistakes to Avoid

1. Wrong locale parameter:

   // ❌ Wrong - locale doesn't match expected language
   new LanguageExistRule('en') // When expecting 'fa'
   
   // ✅ Correct - locale matches expected language
   new LanguageExistRule('fa')

2. Not allowing zero when needed:

   // ❌ Wrong - will fail if user selects "no language"
   'language_id' => [new LanguageExistRule('en', false)]
   
   // ✅ Correct - allows 0 for optional language
   'language_id' => ['nullable', new LanguageExistRule('en', true)]

3. Using for locale validation:

   // ❌ Wrong - this rule validates language_id, not locale
   'locale' => [new LanguageExistRule('en')]
   
   // ✅ Correct - use CheckLocaleRule for locale
   'locale' => [new CheckLocaleRule]

4. Missing 'required' or 'nullable':

   // ❌ Wrong - unclear if field is required
   'language_id' => [new LanguageExistRule('en')]
   
   // ✅ Correct - explicit requirement
   'language_id' => ['required', 'integer', new LanguageExistRule('en')]

Comparison with CheckLocaleRule

Rule	Validates	Use Case
CheckLocaleRule	Locale format and uniqueness	Creating/updating language records
LanguageExistRule	Language ID existence and locale match	Foreign key validation in related models

Related Documentation

• CheckLocaleRule
• Language Model