Mongodb查询文档if field是否不存在

Question

我有一个包含范信息的文件

1. 它有一个区域数组字段
2. 在每个数组中，我都有积分，分数

喜欢这个

name: "test',
address:"test",
"area" : [ 
    {
        "end_point_click" : "(10.577011981272062, 76.03049470111728)",
        "description_of_work" : "dfgfdgd",
        "head_area" : "Thrissur",
        "start_point_click" : "(10.525709313612015, 76.22000886127353)",
        "route_name" : "Thrissur Guruvayoor",
        "start_location" : "Thrissur",
        "end_location" : "Guruvayoor",
        "lead_info" : [ 
            {
                "latlng" : "(10.575054561328756,76.08472825493664)",
                "unique_key" : "Ammu,Paru,fdh,43543534"
            }
        ]
    }, 
    {
        "end_point_click" : "(10.335815561982484, 76.22000886127353)",
        "description_of_work" : "dgdf",
        "head_area" : "Thrissur",
        "start_point_click" : "(10.516663022805359, 76.21451569721103)",
        "route_name" : "Thrissur Irinjalakuda",
        "start_location" : "Thrissur",
        "end_location" : "Irinjalakuda"
    }, 
    {
        "end_point_click" : "(10.554061845632159, 76.3614578358829)",
        "description_of_work" : "dfsfdfs",
        "head_area" : "Thrissur",
        "start_point_click" : "(10.516257889923311, 76.21726227924228)",
        "route_name" : "Thrissur Pattikadu",
        "start_location" : "Thrissur",
        "end_location" : "Pattykadu"
    }
]

我想在json中循环标记。

使用此代码检索它：

  markret = list(collectionnew.find(


             { 'area': 
                 { '$elemMatch':
                     { 'route_name': post_text }
                 }
             },{ '_id':0 , 
                 'area' : 
                 {
                     '$elemMatch':
                     {'route_name': post_text}
                     }}
        ));

您可以在上面的一个文档中注明包含区域+潜在客户信息

"lead_info" : [ 
            {
                "latlng" : "(10.575054561328756,76.08472825493664)",
                "unique_key" : "Ammu,Paru,fdh,43543534"
            }
        ]

其他文档在解析json响应时不包含

if (typeof (JSON.stringify(data[0][0].lead_info[0].latlng)) != 'undefined')

如果该字段不存在则产生错误，我该如何解决。