duai0935 2016-10-07 01:56
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需要使用mgo在删除中使用$ add和$ gt(Golang && MongoDB)

I'm using Golang as my backend and MongoDB as the database for my web application. I'm in need of adding two values and check if the value in the database is greater than the added value and if it is, I need to remove the row from the MongoDB.
The code which I wrote is as follows

err, err1 := c.RemoveAll(bson.M{
        "currenttime": bson.M{
            "$gt": bson.M{
                "$add": []interface{}{time.Now().Unix(),"100"},
            },
        },
     })

FYI: I wrote the sample code for MongoDB but this is not working as well

db.Collection.remove(
   {currenttime:{
        $gt:{
                $add:[100,100]
             }
              }
    }
 )

Please let me know if this is possible. And please give me any alternative way to do this.
Thanks

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  • doufu1950 2016-10-07 05:44
    关注

    1- If you need to remove rows with field e.g. time > t + 10 from the MongoDB, you do't need $add, you may use:

    info, err := c.RemoveAll(bson.M{"time": bson.M{"$gt": t + 10}})
    if err != nil {
        panic(err)
    }
    

    Here is the working code:

    package main
    
    import (
        "fmt"
        "time"
    
        "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("Model")
        c.DropCollection()
        t := time.Now().UTC().Unix()
        err = c.Insert(
            &Model{bson.NewObjectId(), "n1", t},
            &Model{bson.NewObjectId(), "n2", t + 50},
            &Model{bson.NewObjectId(), "n3", t + 100},
            &Model{bson.NewObjectId(), "n4", t + 150})
        if err != nil {
            panic(err)
        }
        r := []Model{}
        err = c.Find(nil).All(&r)
        if err != nil {
            panic(err)
        }
        fmt.Println(r)
    
        info, err := c.RemoveAll(bson.M{"time": bson.M{"$gt": t + 10}})
        if err != nil {
            panic(err)
        }
        fmt.Println(info)
    
        r2 := []Model{}
        err = c.Find(nil).All(&r2)
        if err != nil {
            panic(err)
        }
        fmt.Println(r2)
    }
    
    type Model struct {
        ID   bson.ObjectId `json: "_id,omitempty" bson: "_id,omitempty"`
        Name string        `json: "name" bson: "name"`
        Time int64         `json: "time" bson: "time"`
    }
    

    output:

    [{ObjectIdHex("57f7354cc3176906c0ca7516") n1 1475818828} {ObjectIdHex("57f7354cc3176906c0ca7517") n2 1475818878} {ObjectIdHex("57f7354cc3176906c0ca7518") n3 1475818928} {ObjectIdHex("57f7354cc3176906c0ca7519") n4 1475818978}]
    &{0 3 3 <nil>}
    [{ObjectIdHex("57f7354cc3176906c0ca7516") n1 1475818828}]
    

    2- For $add, see:
    Query where sum of two fields is less than given value
    https://docs.mongodb.com/manual/reference/operator/aggregation/add/

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论
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