laravel query with relationship code example

Example 1: how to use where relationship laravel

Event::with(["owner", "participants" => function($q) use($someId){
    $q->where('participants.IdUser', '=', 1);
    //$q->where('some other field', $someId);
}])

Example 2: where query from relation table in laravel

UserModel::whereHas('attachments', function ($attachmentQuery) {
    $attachmentQuery->where('level', 'profile_level');
})->get();
If you want from already queried model get specific attachments then write

$userModel->attachments()->where('level', 'profile_level')->get();

it is impossible to query both UserModel and AttachementModel in single query,
it must be at least two queries. Even fancy 
  UserModel::with('attachments')->get();, 
which returns user with all attachments, do internally two queries.

OR:

I noticed that you can define relation constraints within with method

UserModel::with(['attachments' => function ($attachmentQuery) {
    $attachmentQuery->where('level', 'profile_level');
}])->get();

Example 3: whereHas site:https://laravel.com/docs/

use Illuminate\Database\Eloquent\Builder;

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

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

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: laravel how to query belongsTo relationship

$movies = Movie::whereHas('director', function($q) {
    $q->where('name', 'great');
})->get();

Example 6: eloquent relationships

$roles = App\User::find(1)->roles()->orderBy('name')->get();