{
    "_id": "590ad2c78eb79d16bde4a15d",
    "user": "yejia@qq.com",
    "password": "111111",
    "__v": 0,
    "lists": [
      {
        "_id": "590ad2d78eb79d16bde4a15e",
        "update_at": "2017-05-04T07:05:52.174Z",
        "create_at": "2017-05-04T07:05:52.174Z",
        "title": "测试1",
        "isChecked": [
          false
        ],
        "details": [
          "未完"
        ]
      },
      {
        "_id": "590ad3398eb79d16bde4a15f",
        "update_at": "2017-05-04T07:07:28.784Z",
        "create_at": "2017-05-04T07:07:28.784Z",
        "title": "测试2",
        "isChecked": [
          false,
          false
        ],
        "details": [
          "1232",
          "333"
        ]
      }
    ]
  }

像这个例子，如果我要根据子文档的id："_id": "590ad2d78eb79d16bde4a15e"查找子文档，该怎么操作？说明一下，直接用id查询我会，我不懂的是用子文档的id查询子文档。