MongoDB：查找返回重复值的查询

Question

我有一个具有以下结构的MongoDB：

db.http_methods.find({"methods.head.status":"200"}, {"methods.head.$":1}).pretty();

说明此查询时

{
    "_id" : ObjectId("591ec4b8e1f71c0caf406f2a"),
    "methods" : {
        "head" : [
            {
                "host" : "127.0.0.1",
                "port" : "8081",
                "protocol" : "http:",
                "path" : "/index.html",
                "method" : "HEAD",
                "status" : "200"
            }
        ]
    }
}

我重复了三次以下输出：

db.http_methods.find({_id:ObjectId("591ec4b8e1f71c0caf406f2a‌​"), "methods.head.status":"200"}, {"methods.head.$":1}).pretty()

任何想法为什么？

编辑：并使用此查询

  [main] Error: invalid object id: length :

我收到错误：

    +----------------------+------------+
    | input                | output     |
    +----------------------+------------+
    | www.google.com       | google     |
    | www.mail.yahoo.com   | mail.yahoo |
    | www.mail.yahoo.co.in | mail.yahoo |
    | www.abc.au.uk        | abc        |
     www.subdoamin.domain.co.in     // output subdomain