Golang MongoDB聚合 [英] Golang mongodb aggregation
问题描述
我有一组用户.用户有一个int64"id",并说"avatar","name"和其他用户ID的数组. 我想要实现的是查询SINGLE用户,但与其获取带有其朋友ID的数组,不如获取一个包含其姓名和头像的朋友的数组.如何在golang中实现它?我已经找到了我需要的某种东西-查找"功能,但是我不明白如何正确使用它.
I have a collection of users. User have an int64 "id", and lets say "avatar", "name" and an array of other users ids. What I want to achieve is to query SINGLE user, but instead of getting an array with his friends ids I want to get an array of his friends, containing their names and avatars. How to achieve it in golang? I have found some kind of what I need - "lookup" function, but I cannot understand how to use it right.
推荐答案
您不能应用 $ unwind 首先.
You cannot apply $lookup to array directly, but you can to $unwind it first.
没有示例文档,下面的代码段是一种通用方法:
Without example documents, the code snippet below is rather a general approach:
pipeline := []bson.M{
bson.M{"$match": bson.M{"_id": userId }},
bson.M{"$unwind": "$otherUsersIdsArrayName"},
bson.M{
"$lookup": bson.M{
"from": userCollectionName,
"localField": otherUsersIdsArrayName,
"foreignField": "id",
"as": "friend"
}
},
bson.M{"$unwind": "$friend"},
bson.M{
"$group": bson.M{
"_id": "id",
"id": bson.M{"$first": "$id"},
"name": bson.M{"$first": "$name"},
"avatar": bson.M{"$first": "$avatar"},
otherUsersIdsArrayName: bson.M{ "$push": "$friend"}
}
}
}
pipe := collection.Pipe(pipeline)
resp := []bson.M{}
err = pipe.All(&resp)
我应该提到聚合/管道返回的是bson.M
,而不是水合的User对象. Mongo毕竟不是关系数据库.
I should mention that aggregation/pipe returns bson.M
, not hydrated User objects. Mongo is not a relational database after all.
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