如何在 erlang MongoDB 驱动程序中实现聚合

Question

I am trying to use aggregate with the erlang mongodb driver . This is what I have tried so far

mongo_query:command({Db, Conn}, {aggregate,<<"users">>,pipeline, <<"{$group:{_id:\"\", id: {$sum: \"$id\"}} }, {$project:{ _id:0, id: \"$id\"}}">>}, false).

but I recieve this error

** exception error: {bad_command,{errmsg,<<"exception: wrong type for field (pipeline) 2 != 4">>,
                                         code,13111,ok,0.0}}

I am having trouble moving forward and am looking for any help with a way to implement aggregate with the erlang driver.

Just to be clear I am trying to implement this

db.users.aggregate({$group:{_id:"", id: {$sum: "$id"}} }, {$project:{ _id:0, id: "$id"}});

which works in the MongoDB shell.

Answer 1

如果有人插话，我会听从知道 erlang 的人的意见，但由于没有人：我认为您正在为驱动程序期望列表的管道参数提供一个字符串。

Answer 2

你应该尝试这样的事情：
mongo:command(Connection, {aggregate,<<"users">>,pipeline, [{'$group',{'_id', id, {'$sum', '$id'}}}, {'$project',{'_id',0, id, '$id'}}]}).