计算 Laravel Eloquent 中所有根父节点的所有第 n 个子节点的数量

Question

我有一个来自 Laravel Eloquent 查询的集合。这里祖父有很多孩子（父亲），父亲有很多孩子（孙子）。 返回的结果是这样的：

    [
  {
    "grand_father_id": "26",
    "fathers": [
      {
        "father_id": "101",
        "children": [
          {
            "child_id": "77",
            "children_weight": [
              {
                "weight": "30.00",
              }
            ]
          },
          {
            "child_id": "84",
            "children_weight": [
              {
                "weight": "20.00",
              }
            ]
          }
        ]
      },
      {
        "father_id": "102",
        "children": [
          {
            "child_id": "78",
            "children_weight": [
              {
                "weight": "50.00",
              }
            ]
          }
        ]
      }
    ]
  },
  {
    "grand_father_id": "27",
    "fathers": [
      {
        "father_id": "100",
        "children": [
          {
            "child_id": "83",
            "children_weight": [
              {
                "weight": "100.00",
              }
            ]
          }
        ]
      }
    ]
  },
  {
    "grand_father_id": "28",
    "fathers": [
      {
        "father_id": "105",
        "children": [
          {
            "child_id": "81",
            "children_weight": [
              {
                "weight": "80.00",
              }
            ]
          },
          {
            "child_id": "82",
            "children_weight": [
              {
                "weight": "0.00",
              }
            ]
          }
        ]
      }
    ]
  },
  {
    "grand_father_id": "29",
    "fathers": [
      {
        "father_id": "108",
        "children": [
          {
            "child_id": "79",
            "children_weight": [
              {
                "weight": "44.00",
              }
            ]
          },
          {
            "child_id": "80",
            "children_weight": [
              {
                "weight": "56.00",
              }
            ]
          }
        ]
      }
    ]
  },
  {
    "grand_father_id": "30",
    "fathers": [
      {
        "father_id": "107",
        "children": [

        ]
      }
    ]
  }
]

我如何计算所有祖父的所有孙子的总数。我当然可以使用嵌套循环来计算这个。但是还有其他 Laravel Collection 方法可以做到这一点吗？顺便说一句，我在这里举的祖父、父亲、孙子的例子只是一个假名的例子。真正的字段是objectives、actions、success_indicators、success_indicator_weight。获取集合的查询是：

return Objective::with([
        'actions' => function($query) {
        $query->select(['action_id', 'action_description', 'objective_id_fk']);
    }, 'actions.successIndicators' => function($query) {
        $query->select('success_indicator_id', 'success_indicator_description', 'action_id_fk');
    }, 'actions.successIndicators.SuccessIndicatorYearWeight' => function($query) {
        $query->select('success_indicator_weight', 'success_indicator_unit', 'success_indicator_id_fk');
    },
])->get()

Answer 1

有很多 array_* 辅助方法可用于对嵌套数组执行各种操作，但我认为没有任何东西可以满足您的需求。你可以自己检查 - http://laravel.com/docs/5.0/helpers#arrays

我不知道 Collection 是否内置了任何东西，但您可以考虑每个 Grandfather 类的访问器方法：

class Grandfather extends Eloquent
{
    ...
    public function getTotalGrandchildrenAttribute()
    {
        $total_grandchildren = 0;
        // loop through each father
        foreach ($this->fathers as $father) {
            $total_grandchildren += count($father->children);
        }
        return $total_grandchildren;
    }
}

然后在你的脚本中：

$grandfathers = Grandfathers::all();

$total_grandchildren = 0;
foreach ($grandfathers as $grandfather) {
    $total_grandchildren += $grandfather->total_grandchildren;
}

echo "Total grandchildren: $total_grandchildren";

http://laravel.com/docs/5.0/eloquent#accessors-and-mutators

此外，您可能希望使用with('fathers') 和with('children') 而不是使用上面显示的 all()，这样您就不会在每次想要获取父亲/孩子时都访问数据库：

$grandfathers = Grandfathers::with(array('fathers' => function($query) {
    $query->with('children');
});

http://laravel.com/docs/5.0/eloquent#eager-loading