Eloquent Relationship Queries in Laravel with whereRelation

Laravel's whereRelation method simplifies filtering models based on their related data. This elegant solution replaces complex joins and subqueries with a cleaner, more maintainable syntax. It's particularly useful for building sophisticated filters in applications with interconnected models, such as e-commerce sites or content management systems.

Consider this concise example:

Post::whereRelation('comments', 'is_approved', true)->get();

This retrieves all Post models where at least one associated comment has is_approved set to true.

Let's illustrate with a course filtering system:

<?php namespace App\Http\Controllers;

use App\Models\Course;
use Illuminate\Http\Request;

class CourseController extends Controller
{
    public function browse(Request $request)
    {
        $courses = Course::query();

        // Filter by instructor rating
        if ($request->has('top_rated')) {
            $courses->whereRelation('instructor', 'rating', '>=', 4.5);
        }

        // Filter by recent student reviews
        if ($request->has('well_reviewed')) {
            $courses->orWhereRelation('reviews', 'created_at', '>=', now()->subDays(30));
        }

        // Filter by active discussion
        if ($request->has('active_discussion')) {
            $courses->whereRelation('discussions', 'last_activity', '>=', now()->subDays(7));
        }

        return $courses->with(['instructor', 'reviews'])->latest()->paginate();
    }
}

This controller method demonstrates how to build dynamic filters. The generated SQL is highly efficient, handling the relationship conditions effectively. For instance:

// Filters courses with:
// - Highly rated instructors (4.5+)
// - OR recent reviews (within the last 30 days)
// - AND active discussions (within the last 7 days)
$courses = Course::whereRelation('instructor', 'rating', '>=', 4.5)
    ->orWhereRelation('reviews', 'created_at', '>=', now()->subDays(30))
    ->whereRelation('discussions', 'last_activity', '>=', now()->subDays(7))
    ->get();

In summary, whereRelation offers a clear and expressive method for filtering models based on relationship attributes, resulting in cleaner, more maintainable Laravel applications.

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