小编SUR*_*AJU的帖子

字段的数据类型是String.我想获取字段名称的字符长度大于40的数据.

我尝试了这些查询但返回错误.1.

db.usercollection.find(
{$where: "(this.name.length > 40)"}
).limit(2);

output :error: {
    "$err" : "TypeError: Cannot read property 'length' of undefined near '40)' ",
    "code" : 16722
}

这是在2.4.9但我的版本是2.6.5

我有一个类似的mongo文件

{ "_id" : 12, "location" : [ "Kannur","Hyderabad","Chennai","Bengaluru"] }
{ "_id" : 13, "location" : [ "Hyderabad","Chennai","Mysore","Ballary"] }

从这里我如何获得位置聚合(不同的区域计数).就像是

Hyderabad 2, 
Kannur 1, 
Chennai 2, 
Bengaluru 1, 
Mysore 1, 
Ballary 1