Laravel ORM从自引用表获取N级层次结构JSON

我在用LARAVEL 4 with MySQL后端。

我有一个self-referencing带列的表id, name, type and parent. Here, parent is foreign-key列的Id。表中数据如下：

id  name          type         parent 
1   General       group        NULL
2   What is..?    question     1
3   aa            answer       2
4   bb            answer       2
5   cc            answer       2
6   How is..?     question     1
7   ba            answer       6
8   bb            answer       6
9   Where is..?   question     4
10  ca            answer       9
11  cb            answer       9
12  Who is..?     question     6
13  da            answer       12
14  db            answer       12
15  Specific      group        NULL
16  When is..?    question     15
17  ea            answer       16
18  eb            answer       16
19  Whome is..?   question     2
20  fa            answer       19
21  fb            answer       19
22  fc            answer       19

我想要一个返回的函数nested JSON使用此关系数据。例如 ：

[{
  "id" : 1, 
  "name" : "Geneal", 
  "type" : "group", 
  "children" : [{
      "id" : 2, 
      "name" : "What is..?", 
      "type" : "question", 
      "children" : [{
         "id" : 3, 
         "name" : "aa", 
         "type" : "answer"
      },
      {
         "id" : 4, 
         "name" : "bb", 
         "type" : "answer"
      },
      {
         "id" : 5, 
         "name" : "cc", 
         "type" : "answer"
      }]},
      {
      "id" : 6, 
      "name" : "How is..?", 
      "type" : "question", 
      "children" : [{
         "id" : 7, 
         "name" : "ba", 
         "type" : "answer"
      },
      {
         "id" : 8, 
         "name" : "bb", 
         "type" : "answer"
      }]
   }]
... and so on
}]

我创建了一个model named Survey如下 ：

class Survey extends BaseModel{

    protected $table = 'questions';
    protected $softDelete = false;

    public function parent()
    {
        return $this->belongsTo('Survey', 'parent');
    }

    public function children()
    {
        return $this->hasMany('Survey', 'parent');
    }   
}

并调用它controller with :

$user = Survey::all();
$parent = $user->parent()->first();
$children = $user->children()->get();

但我没有得到正确的结果，正如我在JSON above.

print_r($parent->toJson()); 

仅给出具有一级层次结构的记录（即组和问题，而不是答案）。

while

print_r($children ->toJson());

仅给出问题（不给出组和答案）。

我想要整个具有 N 层层次结构的嵌套 JSON 格式的自引用数据.

我也尝试过

$user = Survey::with('parent', 'children')->get();

但发现与上面的 $parent 相同。

无论如何我可以获得想要的结果吗？

提前致谢..

以下是手动检索嵌套关系的方法：

$collection = Model::with('relation1.relation2.relation3')->get();

所以在你的情况下它将是：

$surveys = Survey::with('children.children.children')->get();

显然，当关系固定时，这可以完成工作，但这不是与同一个表建立递归关系的方法。

幸运的是，你可以使这种关系递归，那么检索整个树所需的就是这样：

$surveys = Survey::with('childrenRecursive');

但是，我不会以这种方式加载每一行的父级。

所以这就是您所需要的：

// Survey model
// loads only direct children - 1 level
public function children()
{
   return $this->hasMany('Survey', 'parent');
}

// recursive, loads all descendants
public function childrenRecursive()
{
   return $this->children()->with('childrenRecursive');
   // which is equivalent to:
   // return $this->hasMany('Survey', 'parent')->with('childrenRecursive);
}

// parent
public function parent()
{
   return $this->belongsTo('Survey','parent');
}

// all ascendants
public function parentRecursive()
{
   return $this->parent()->with('parentRecursive');
}

编辑：要获得真正的树结构，第一个查询必须仅限于根节点：

$surveys = Survey::with('childrenRecursive')->whereNull('parent')->get();