Laravel 8 Eloquent Guide

Eloquent simplifies database operations. Advanced relationships and query techniques unlock powerful capabilities. At ZIRA Software, mastering Eloquent optimizations improved application performance by 10x.

Polymorphic Relationships

One-to-many polymorphic:

// Commentable interface
class Post extends Model {
    public function comments() {
        return $this->morphMany(Comment::class, 'commentable');
    }
}

class Video extends Model {
    public function comments() {
        return $this->morphMany(Comment::class, 'commentable');
    }
}

class Comment extends Model {
    public function commentable() {
        return $this->morphTo();
    }
}

// Usage
$post = Post::find(1);
$post->comments; // All comments for this post

$comment = Comment::find(1);
$comment->commentable; // Post or Video

Many-to-many polymorphic:

class Tag extends Model {
    public function posts() {
        return $this->morphedByMany(Post::class, 'taggable');
    }

    public function videos() {
        return $this->morphedByMany(Video::class, 'taggable');
    }
}

// Usage
$tag = Tag::find(1);
$tag->posts; // All posts with this tag
$tag->videos; // All videos with this tag

Subquery Selects

// Get latest post for each user
$users = User::addSelect(['latest_post_title' => Post::select('title')
    ->whereColumn('user_id', 'users.id')
    ->latest()
    ->limit(1)
])->get();

// Order by subquery
$users = User::orderByDesc(
    Post::select('created_at')
        ->whereColumn('user_id', 'users.id')
        ->latest()
        ->limit(1)
)->get();

Lazy Eager Loading

$posts = Post::all();

// Later realize you need comments
$posts->load('comments');

// Load with constraints
$posts->load(['comments' => function ($query) {
    $query->where('approved', true);
}]);

// Load count
$posts->loadCount('comments');

Query Scopes

Local scopes:

class Post extends Model {
    public function scopePublished($query) {
        return $query->where('published', true);
    }

    public function scopePopular($query) {
        return $query->where('views', '>', 1000);
    }
}

// Usage
Post::published()->popular()->get();

Advanced Where Clauses

// Subquery where
User::whereIn('id', function ($query) {
    $query->select('user_id')
        ->from('orders')
        ->where('total', '>', 1000);
})->get();

// JSON where
Product::where('metadata->color', 'blue')->get();

// Date where
Order::whereDate('created_at', '2021-03-15')->get();
Order::whereMonth('created_at', 3)->get();

Conclusion

Advanced Eloquent techniques solve complex data requirements elegantly. Master these patterns for optimal Laravel development.

Need database optimization? Contact ZIRA Software for performance consultation.