with function in laravel code example

Example 1: laravel wherehas

$users = User::whereHas('posts', function($q){
    $q->where('created_at', '>=', '2015-01-01 00:00:00');
})->get();
// only users that have posts from 2015 on forward are returned

Example 2: laravel where has

use Illuminate\Database\Eloquent\Builder;

// Retrieve posts with at least one comment containing words like foo%...
$posts = App\Post::whereHas('comments', function (Builder $query) {
    $query->where('content', 'like', 'foo%');
})->get();

// Retrieve posts with at least ten comments containing words like foo%...
$posts = App\Post::whereHas('comments', function (Builder $query) {
    $query->where('content', 'like', 'foo%');
}, '>=', 10)->get();

Example 3: one to many laravel

For example, a blog post may have an infinite number of comments. And a single
comment belongs to only a single post  

class Post extends Model
{
    public function comments()
    {
        return $this->hasMany('App\Models\Comment');
    }
}

class Comment extends Model
{
    public function post()
    {
        return $this->belongsTo('App\Models\Post');
    }
}

Example 4: associate laravel

When updating a belongsTo relationship, you may use the associate method. This 
method will set the foreign key on the child model:

	$account = App\Account::find(10);
	$user->account()->associate($account);
	$user->save();

When removing a belongsTo relationship, you may use the dissociate method. This
method will set the relationship foreign key to null:

	$user->account()->dissociate();
	$user->save();

Example 5: by default null eloquent user data in relationship in laravel 8

# simple handle in blade file 
{{ $post->author->name or 'No author' }}

# Model action 
public function author()
{
    return $this->belongsTo('App\Author')->withDefault();
}

public function author()
{
    return $this->belongsTo('App\Author')->withDefault([
        'name' => 'Guest Author',
    ]);
}