使用聚合我正在使用golang加入两个mongodb集合。结果如下所示: -
输出: -
{
"response": {
"code": 1,
"api_status": 1,
"message": "Success",
"total_record": [
{
"_id": 1,
"author_name": "mohit",
"category": 232,
"content": "This is the content",
"date_time": 1524632713,
"excerpt": "This is a short text",
"image": "pic.jpg",
"resultField": [
{
"_id": 6,
"comment": "this is a least comment",
"comment_on": 1524644601,
"email": "puneet@bookingkoala.com",
"name": "puneet",
"post_id": 1,
"reply_to": 1524644601,
"status": 1
},
{
"_id": 7,
"comment": "this is a least comment",
"comment_on": 1524647808,
"email": "puneet@bookingkoala.com",
"name": "puneet",
"post_id": 1,
"reply_to": 1524647808,
"status": 1
}
],
"status": 0,
"tags": "this",
"title": "how to do the code"
},
{
"_id": 2,
"author_name": "mohit",
"category": 232,
"content": "This is the content",
"date_time": 1524632713,
"excerpt": "This is a short text",
"image": "pic.jpg",
"resultField": [
{
"_id": 8,
"comment": "this is a least comment",
"comment_on": 1524648059,
"email": "puneet@bookingkoala.com",
"name": "puneet",
"post_id": 2,
"reply_to": 1524648059,
"status": 1
}
],
"status": 0,
"tags": "this",
"title": "how to do the code"
},
{
"_id": 3,
"author_name": "puneet",
"category": 2,
"content": "this is content",
"date_time": 1524641086,
"excerpt": "this is excerpt",
"image": "pic.jpg",
"resultField": [],
"status": 1,
"tags": "go",
"title": "how to do the code"
}
]
}
}
此输出由以下golang代码执行: -
mongoSession := config.ConnectDb()
collection := mongoSession.DB(config.Database).C(config.BlogCollection)
pipeline := []bson.M{
bson.M{"$match": bson.M{}},
bson.M{"$lookup": bson.M{"from" : "comment", "localField" : "_id", "foreignField": "post_id","as": "resultField" }},
}
fmt.Println(pipeline)
pipe := collection.Pipe(pipeline)
resp := []bson.M{}
err = pipe.All(&resp)
if err != nil {
fmt.Println("Errored: %#v \n", err)
}
fmt.Println(resp)
if err != nil {
response = ResponseControllerList{
config.FailureCode,
config.FailureFlag,
config.FailureMsg,
nil,
nil,
}
} else {
response = ResponseControllerList{
config.SuccessFlag,
config.SuccessFlag,
config.SuccessMsg,
nil,
resp,
}
}
问题是: - 我只需要count
的data
而不是 data
。输出中的平均值如上所示有resultField
,其中显示了数据,但我只需要count
值,如: - "resultField":[2]
但它显示的是数据。如何获取输出中数据的计数值。提前谢谢。
答案 0 :(得分:0)
因此,您的聚合实际上会返回comment
字段中的所有resultField
个文档,其中隐含地包含结果的数量,它是一个切片,您可以使用内置函数检查Go中的长度len()
功能。
由于您只需要长度(comment
个文档的数量),这就是您只想检索此数组大小的原因。为此,您可以使用$addFields
阶段将resultField
数组替换为数字,即该数组的长度。
pipe := c.Pipe([]bson.M{
{
"$lookup": bson.M{
"from": "comment",
"localField": "_id",
"foreignField": "post_id",
"as": "resultField",
},
},
{
"$addFields": bson.M{
"resultField": bson.M{"$size": "$resultField"},
},
},
})
请注意,$addFields
阶段等同于$project
阶段,该阶段明确指定输入文档中的所有现有字段并添加新字段。仅在MongoDB版本3.4之后可用。