Query Models Based on Related Model Existence

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;

class Product extends Model
{
    use HasFactory;

    public function reviews()
    {
        return $this->hasMany(Review::class);
    }
}

class Review extends Model
{
    use HasFactory;

    protected $fillable = ['product_id', 'rating', 'comment'];

    public function product()
    {
        return $this->belongsTo(Product::class);
    }
}

// Example usage in a controller or service:
/*
// Get products that have at least one review
$productsWithReviews = Product::has('reviews')->get();

// Get products that have no reviews
$productsWithoutReviews = Product::doesntHave('reviews')->get();

// Get products that have reviews with a specific condition (e.g., rating >= 4)
$highlyRatedProducts = Product::whereHas('reviews', function ($query) {
    $query->where('rating', '>=', 4);
})->get();

// Get products that do NOT have any reviews with a specific condition (e.g., no reviews with rating < 3)
$noLowRatedReviews = Product::whereDoesntHave('reviews', function ($query) {
    $query->where('rating', '<', 3);
})->get();

// Eager load reviews for products that have them
$productsWithReviewsAndData = Product::with('reviews')->has('reviews')->get();

// Count related models
$productsWithReviewCount = Product::withCount('reviews')->get();
foreach ($productsWithReviewCount as $product) {
    // $product->reviews_count will contain the number of reviews
}
*/