MongoDB从层次结构模型中获取所有文档

Question

目前我们的收集结构如下所示

db.testcol.insert({"name":"root_node","ip":"10.10","addr":"123 Node12"});
db.testcol.insert({"name":"first_level_1","ip":"10.10","addr":"123 Node12","parent_name":"root_node"});
db.testcol.insert({"name":"second_level","ip":"10.10","addr":"123 Node12","parent_name":"first_level_1"});
db.testcol.insert({"name":"first_level_2","ip":"10.11","addr":"13 Node123","parent_name":"root_node"});
db.testcol.insert({"name":"second_level_1","ip":"10.11","addr":"13 Node123","parent_name":"first_level_2"});
db.testcol.insert({"name":"third_level_l","ip":"10.11","addr":"13 Node123","parent_name":"second_level_1"});
db.testcol.insert({"name":"third_level_2","ip":"10.11","addr":"13 Node123","parent_name":"second_level_1"}); 

现在我将从前端传递根节点，我将显示level1，level2 ... level n文档。请告诉我怎么做。

在这个示例文档中，我将使用“root_node”进行搜索。它应该显示我要显示first_level，second_level和third_level文档。 Parent_name是关系键。

Edit:  Expected Output:  Input is "root_node" 

-- First level children for "root_node"

       /* 0 */
    {
        "_id" : ObjectId("56654b5b1160f16ccd252685"),
        "name" : "first_level_1",
        "ip" : "10.10",
        "addr" : "123 Node12",
        "parent_name" : "root_node"
    }

    /* 1 */
    {
        "_id" : ObjectId("56654b5b1160f16ccd252687"),
        "name" : "first_level_2",
        "ip" : "10.11",
        "addr" : "13 Node123",
        "parent_name" : "root_node"
    }

   -- Second level documents -- parent is  second_level1 and second_leve2
    /* 0 */
    {
        "_id" : ObjectId("56654b5b1160f16ccd252686"),
        "name" : "second_level",
        "ip" : "10.10",
        "addr" : "123 Node12",
        "parent_name" : "first_level_1"
    }

    /* 0 */
    {
        "_id" : ObjectId("56654b5b1160f16ccd252688"),
        "name" : "second_level_1",
        "ip" : "10.11",
        "addr" : "13 Node123",
        "parent_name" : "first_level_2"
    }

    /* 0 */
    {
        "_id" : ObjectId("56654b5b1160f16ccd252689"),
        "name" : "third_level_l",
        "ip" : "10.11",
        "addr" : "13 Node123",
        "parent_name" : "second_level_1"
    }

    /* 1 */
    {
        "_id" : ObjectId("56654b5b1160f16ccd25268a"),
        "name" : "third_level_2",
        "ip" : "10.11",
        "addr" : "13 Node123",
        "parent_name" : "second_level_1"
    }