Laravel - select with relationship with one query

问题

I have a Person model. Each person may have zero or more cars:

class Person extends Model
{
    public function cars()
    {
        return $this->hasMany('App\Car');
    }
}

I wish to select and display all persons who have a ford with one running query. So i tried this:

$persons = Person::whereHas('cars', function ($query) {
    $query->where('mark', 'ford');
})->get();

foreach ($persons as $person) {
    foreach($person->cars()->get() as $car) {
        print $person->name . " has a " . $car->mark . $car->model
    } 
}

The $persons is gotten with one query, but inside the foreach loop $person->cars()->get() creates a new query for each person. How can i avoid this and get the needed car data with the first query?

回答1:

You have to add the mark filter to whereHas() and with():

$persons = Person::whereHas('cars', function ($query) {
    $query->where('mark', 'ford');
})->with(['cars' => function($query) {
    $query->where('mark', 'ford');
}])->get();

回答2:

The issue is in cars()

Use the below given snippet

foreach ($persons as $person) {
     foreach($person->cars as $car) 
       { 
         print $person->name . " has a " . $car->mark . $car->model
        } 
      }

When u do cars() it refers to model which execute another query. But when u use cars it only refers to collection which is already loaded.

Hope this helps

回答3:

it is worth examining : laravel Eager Loading

When used in this manner will come in a query relational data.

Example:

Person::with('cars')->get();

This code response: Person data with Person's Car data

来源：https://stackoverflow.com/questions/49563701/laravel-select-with-relationship-with-one-query