Question

在Laravel 4中，我使用Eager Loading来实现ManyToMany关系：

public function categories()
{

    return $this->belongsToMany('Category');

}

它返回如下类别：

    "categories": [
        {
            "id": 1,
            "priority": 1,
            "title": "My category 1",
            "created_at": "2013-08-10 18:45:08",
            "updated_at": "2013-08-10 18:45:08"
        },
        {
            "id": 2,
            "priority": 2,
            "title": "My category 2",
            "created_at": "2013-08-10 18:45:08",
            "updated_at": "2013-08-10 18:45:08"
        }
    ],

但我所需要的只是：

    "categories": [1,2] // References category id's only

查询生成器有一个名为“列表”的方法，应该可以解决这个问题。但是在Eager Load ???的情况下它不起作用

public function categories()
{

    return $this->belongsToMany('Category')->lists('category_id');

}

Answer 1

它不起作用的原因是因为当急切加载它时，使用with方法，Laravel期望一个关系方法返回一个Illuminate\Database\Eloquent\Relations\Relation对象，以便它可以调用{{1 }} 在上面。当您调用get时，查询已经运行，而返回的内容则是数组。

为减少数据传输，您可以执行的操作是在查询上使用lists方法，然后在类别集合上运行select。例如：

<强> Model.php

lists

<强> Whatever.php

function categories() {
    return $this->belongsToMany('Category')->select('id');
}

Answer 2

将以下代码添加到Model / BaseModel：

/**
 * Set additional attributes as hidden on the current Model
 *
 * @return instanceof Model
 */
public function addHidden($attribute)
{
    $hidden = $this->getHidden();

    array_push($hidden, $attribute);

    $this->setHidden($hidden);

    // Make method chainable
    return $this;
}

/**
 * Convert appended collections into a list of attributes
 *
 * @param  object       $data       Model OR Collection
 * @param  string|array $levels     Levels to iterate over
 * @param  string       $attribute  The attribute we want to get listified
 * @param  boolean      $hideOrigin Hide the original relationship data from the result set
 * @return Model
 */
public function listAttributes($data, $levels, $attribute = 'id', $hideOrigin = true)
{

    // Set some defaults on first call of this function (because this function is recursive)
    if (! is_array($levels))
        $levels = explode('.', $levels);

    if ($data instanceof Illuminate\Database\Eloquent\Collection) // Collection of Model objects
    {
        // We are dealing with an array here, so iterate over its contents and use recursion to look deeper:
        foreach ($data as $row)
        {
            $this->listAttributes($row, $levels, $attribute, $hideOrigin);
        }
    }
    else
    {
        // Fetch the name of the current level we are looking at
        $curLevel = array_shift($levels);

        if (is_object($data->{$curLevel}))
        {
            if (! empty($levels))
            {
                // We are traversing the right section, but are not at the level of the list yet... Let's use recursion to look deeper:
                $this->listAttributes($data->{$curLevel}, $levels, $attribute, $hideOrigin);
            }
            else
            {
                // Hide the appended collection itself from the result set, if the user didn't request it
                if ($hideOrigin)
                    $data->addHidden($curLevel);

                // Convert Collection to Eloquent lists()
                if (is_array($attribute)) // Use specific attributes as key and value
                    $data->{$curLevel . '_' . $attribute[0]} = $data->{$curLevel}->lists($attribute[0], $attribute[1]);
                else // Use specific attribute as value (= numeric keys)
                    $data->{$curLevel . '_' . $attribute} = $data->{$curLevel}->lists($attribute);
            }
        }
    }

    return $data;
}

您可以在模型/集合对象上使用它，如下所示：

// Fetch posts data
$data = Post::with('tags')->get(); // or use ->first()

// Convert relationship data to list of id's
$data->listAttributes($data, 'tags');

$ data现在将包含以下对象库：

{
    "posts": [
        {
            "title": "Laravel is awesome",
            "body": "Lorem Ipsum...",
            "tags_id": [ 1, 2, 3 ]
        },
        {
            "title": "Did I mention how awesome Laravel is?",
            "body": "Lorem Ipsum...",
            "tags_id": [ 1, 2, 4 ]
        }
    ]
}

它还支持嵌套关系：

// Fetch posts data
$data = Post::with('comments', 'comments.tags')->get(); // or use ->first()

// Convert relationship data to list of id's
$data->listAttributes($data, 'comments.tags');

Answer 3

如果所有请求属于category型号，则可以设置visible array

喜欢protected $visible = array('category_id');

现在，对类别模型的每个请求都只会检索category_id

在你的情况下 -

Class Category extends Eloquent{

    protected $visible=array('category_id');
    ...
}

注意 - 它会将category_id的集合作为对象返回，但如果需要数组，则必须使用toArray()查询构建器方法来获取数组category_id

为了得到你需要的东西，你可以试试这个

$cat_id=Category::all()->toArray();
$arrid=array();
array_walk_recursive($cat_id,function($value,$key) use (&$arrid){
  array_push($arrid,$value);
})
//$arrid will contain only category_id's like
//$arrid=[1,2,3];

Laravel 4中的Eager Load列表（）

3 个答案: