Question

我的mongo文件在这里

 db.aaa.aggregate([{
                $match : {
                    status : "Active"
                }
            }, {
                $project : {
                    _id : 1,
                    title : 1,
                    postdatetime : 1,
                    status : 1,
                    answer : {
                        $filter : {
                            input : "$answer",
                            as : "answe",
                            cond : {
                                $eq : ["$$answe.status", "Active"]
                            }
                        }
                    }
                }
            }
        ])

我试着写一下

o2 := bson.M{
    "$project":bson.M{
        "$answer":bson.M{
                "_id":1,"title":1,"postdatetime":1,"status":1,"answer":bson.M{
                            "$filter":bson.M{"input":"$answer","as":"ans","cond":bson.M{"$eq":bson.M["$$ans.status","Active",],},}
                        },

            },
        },
}

但它显示错误      语法错误：意外逗号，期待]


请帮帮我。
After the answer i try this one

   o2: = bson.M {
    "$project": bson.M {
        "$answer": bson.M {
            "_id": 1,
            "title": 1,
            "revision": 1,
            "bgimageurl": 1,
            "author": 1,
            "postdatetime": 1,
            "status": 1,
            "qatags": 1,
            "followers": 1,
            "qaviews": 1,
            "answer": bson.M {
                "$filter": bson.M {
                    "input": "$answer",
                    "as": "ans",
                    "cond": bson.M {
                        "$eq": "[$$ans.status][,Active]",
                    },
                },
            },

        },
    },
}

这次编译成功但是在运行go文件之后发送给我这个错误信息 2016/05/11 11:04:17 $表达式不允许在$ project的顶层退出状态1

Answer 1

您的代码中有两个错误：

1。 bson.M

中的数组

bson.M["$$ans.status","Active",]会给出Type bson.M is not an expression之类的错误，因为在这种情况下你不需要键值对，所以字符串数组会是一个更好的例子。

尝试：

[]string{"$$ans.status","Active",}

2。逗号

根据https://golang.org/doc/effective_go.html：

词法分析器总是在令牌后插入分号。这可以概括为“如果新行出现在可以结束语句的标记之后，则插入分号”。

如果您在}之后没有添加逗号，则词法分析器会为您插入;，这将导致您当前的问题。

"$filter":bson.M{"input":"$answer","as":"ans","cond":bson.M{"$eq":bson.M{"$$ans.status","Active",},},} // should add a comma at the end of the line

修改后：

"$filter":bson.M{"input":"$answer","as":"ans","cond":bson.M{"$eq":[]string{"$$ans.status","Active",},},},

更新

对于您的第二个问题$expressions are not allowed at the top-level of $project，请注意mongodb中的汇总仅接受array，您可以参考此链接https://docs.mongodb.com/v3.0/reference/operator/aggregation/：

db.collection.aggregate( [ { <stage> }, ... ] )

Answer 2

完成所有这一切后，
工作

mysql> show processlist;
+------+-----------------+----------------------+-------------+---------+----------+------------------------+------------------+
| Id   | User            | Host                 | db          | Command | Time     | State                  | Info             |
+------+-----------------+----------------------+-------------+---------+----------+------------------------+------------------+
|    1 | event_scheduler | localhost            | NULL        | Daemon  | 13200075 | Waiting on empty queue | NULL             |
| 4212 | root            | localhost            | NULL        | Query   |        0 | init                   | show processlist |
| 4214 | root            | xxx.xx.xxx.xxx:50197 | testmysqldb | Sleep   |        1 |                        | NULL             |
| 4215 | root            | xxx.xx.xxx.xxx:50198 | testmysqldb | Sleep   |        3 |                        | NULL             |
+------+-----------------+----------------------+-------------+---------+----------+------------------------+------------------+

如何在go

2 个答案:

1。 bson.M

2。逗号

更新