mongodb 将 where 与不同的列名一起使用

Question

我在 table 中有四个记录，其中一个具有不同的列名（下面的 "usernm"）-

{ "_id" : ObjectId("583d67ec8a2a25b70f6af482"), "username" : "pradyut", "password" : "hello123" }
{ "_id" : ObjectId("583d68328a2a25b70f6af483"), "username" : "google", "password" : "google123" }
{ "_id" : ObjectId("583d71902a7b4dfc334d1ab4"), "usernm" : "praddy", "password": "google123" }
{ "_id" : ObjectId("583d71b82a7b4dfc334d1ab5"), "username" : "some", "password": "some123" }

下面其中命令不起作用

db.users.find({$where:"this.username.length>=2"});

并抛出错误 -

 Error: error: {
"ok" : 0,
"errmsg" : "TypeError: this.username is undefined :\n_funcs3@:1:24\n",
"code" : 139
}

删除 "usernm" 列后，它工作正常

db.users.remove({usernm:"praddy"});

Answer 1

检查该字段是否存在并在之后查询例如

.find({"username" : {$exists:true}, $where :"this.username.length >= 2"})

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