php - Eloquent Laravel - 仅当关系存在时才检索结果

Question

我正在尝试检索分配有轨道的流派列表，我正在使用 whereHas Eloquent 查询，但感觉有点迷茫。

我有以下内容

//model
public function workingGenre() {
    $this->whereHas('tracks', function($query) {
        $query->where('');
    });

    return $this->tracks()->first();
}

//controller (where i am passing variables etc)
$genres = Genre::with('tracks')->get();

//my view
@foreach($genres as $genre)
   {{print_r($genre->workingGenre())}}
@endforeach

我知道我的 Where 是空的，目前我的 print_r 返回以下内容:

                                        1
                                        App\Track Object
 (
[table:protected] => Track
[fillable:protected] => Array
    (
        [0] => id
        [1] => GenreId
        [2] => Title
        [3] => CreatedById
        [4] => SelectedCount
        [5] => ProducerName
        [6] => SourceId
        [7] => Published
    )

[connection:protected] => 
[primaryKey:protected] => id
[perPage:protected] => 15
[incrementing] => 1
[timestamps] => 1
[attributes:protected] => Array
    (
        [id] => 6
        [GenreId] => 4
        [Title] => Guns Up
        [CreatedById] => 1
        [SelectedCount] => 0
        [ProducerName] => 
        [SourceId] => 1
        [Published] => 1
    )

[original:protected] => Array
    (
        [id] => 6
        [GenreId] => 4
        [Title] => Guns Up
        [CreatedById] => 1
        [SelectedCount] => 0
        [ProducerName] => 
        [SourceId] => 1
        [Published] => 1
    )

[relations:protected] => Array
    (
    )

[hidden:protected] => Array
    (
    )

[visible:protected] => Array
    (
    )

[appends:protected] => Array
    (
    )

[guarded:protected] => Array
    (
        [0] => *
    )

[dates:protected] => Array
    (
    )

[dateFormat:protected] => 
[casts:protected] => Array
    (
    )

[touches:protected] => Array
    (
    )

[observables:protected] => Array
    (
    )

[with:protected] => Array
    (
    )

[morphClass:protected] => 
[exists] => 1
[wasRecentlyCreated] => 
)

**And so on**

朝着正确的方向前进会很棒，我发现这些 Eloquent 东西确实很有用，但我很难理解。

谢谢

Answer 1

$genres = Genre::with('tracks')->has('tracks')->get();
    foreach($genres as $genre)
       //do what you need
    endforeach

这样，只有当他们有轨道并且急切加载它们时，您才会获得流派，如果您不想急切加载，请删除 ::with('tracks')