查询两个字段的总和小于给定值的位置 [英] Query where sum of two fields is less than given value
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问题描述
我使用Go语言和MongoDB以及 mgo.v2
驱动程序,并且我有像
I am using Go language and MongoDB with mgo.v2
driver and I have struct like
type MarkModel struct {
ID bson.ObjectId `json: "_id,omitempty" bson: "_id,omitempty"`
Name string `json: "name" bson: "name"`
Sum int `json: "sum" bson: "sum"`
Delta int `json: "delta" bson: "delta"`
}
我需要找到所有位于 Sum + Delta< 1000
为例。目前我加载所有,然后在Go代码中过滤,但我想过滤查询级别。
如何进行查询?
I need to find all where is Sum + Delta < 1000
for example. At the moment I load all and then in Go code I filter but I would like to filter on query level.
How to make that query ?
现在我全部返回
At the moment I return all with
marks := []MarkModel{}
c_marks := session.DB(database).C(marksCollection)
err := c_marks.Find(bson.M{}).All(&marks)
if err != nil {
panic(err)
}
在这里我在for循环中过滤Go代码,但它不是最优的(这是不好的解决方案)。
and here I filter in Go code in for loop but it is not optimal ( it is bad solution ).
推荐答案
sum + delta < 1000
,您可以使用:
To find all where is sum + delta < 1000
, you may use:
pipe := c.Pipe(
[]bson.M{
bson.M{"$project": bson.M{"_id": 1, "name": 1, "sum": 1, "delta": 1,
"total": bson.M{"$add": []string{"$sum", "$delta"}}}},
bson.M{"$match": bson.M{"total": bson.M{"$lt": 1000}}},
})
这里是工作代码:
Here is the working code:
package main
import (
"fmt"
"gopkg.in/mgo.v2"
"gopkg.in/mgo.v2/bson"
)
func main() {
session, err := mgo.Dial("localhost")
if err != nil {
panic(err)
}
defer session.Close()
session.SetMode(mgo.Monotonic, true) // Optional. Switch the session to a monotonic behavior.
c := session.DB("test").C("MarkModel")
c.DropCollection()
err = c.Insert(&MarkModel{bson.NewObjectId(), "n1", 10, 1}, &MarkModel{bson.NewObjectId(), "n2", 20, 2},
&MarkModel{bson.NewObjectId(), "n1", 100, 1}, &MarkModel{bson.NewObjectId(), "n2", 2000, 2})
if err != nil {
panic(err)
}
pipe := c.Pipe(
[]bson.M{
bson.M{"$project": bson.M{"_id": 1, "name": 1, "sum": 1, "delta": 1,
"total": bson.M{"$add": []string{"$sum", "$delta"}}}},
bson.M{"$match": bson.M{"total": bson.M{"$lt": 1000}}},
})
r := []bson.M{}
err = pipe.All(&r)
if err != nil {
panic(err)
}
for _, v := range r {
fmt.Println(v["_id"], v["sum"], v["delta"], v["total"])
}
fmt.Println()
}
type MarkModel struct {
ID bson.ObjectId `json: "_id,omitempty" bson: "_id,omitempty"`
Name string `json: "name" bson: "name"`
Sum int `json: "sum" bson: "sum"`
Delta int `json: "delta" bson: "delta"`
}
输出:
output:
ObjectIdHex("57f62739c22b1060591c625f") 10 1 11
ObjectIdHex("57f62739c22b1060591c6260") 20 2 22
ObjectIdHex("57f62739c22b1060591c6261") 100 1 101
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