Custom mongodb command in golang using gopkg.in/mgo.v2 as string

Question

I was wondering, is there anyway to run my own command (or query) which I have constructed as a string variable using "mgo" in go.

Something like this:

c := session.DB(DBNAME).C(COLLECTION)
c.RUN_COMMAND_AS_STRING("find({username:'vahid'})")

Answer 1

is there anyway to run my own command (or query) which I have constructed as a string variable using "mgo" in go.

You can invoke MongoDB find command , and parsing string of query filter to map[string]interface{} .

For example:

db := session.DB("databaseName")

queryString := `{"username":"sergio"}`
var filter map[string]interface{} 
err = json.Unmarshal([]byte(queryString), &filter)

result := bson.M{}
err = db.Run(bson.D{{"find", "collectionName"}, {"filter", filter}}, &result)
fmt.Println(result)

Alternatively, instead of using find() , depending on your use case, you can also use MongoDB Aggregation Pipeline .

For example:

pipeString := `[{"$match":{"username":"sergio"}}, {"$project":{"newfield":"$username"}}]`

pipe := []bson.M{}
err = json.Unmarshal([]byte(pipeString), &pipe)

coll := session.DB("databaseName").C("collectionName")
response := []bson.M{}
err = coll.Pipe(pipe).All(&response)  
fmt.Println(response)

Answer 2

Here's what I like to use:

func dbInsert(collection string, insert bson.M, session *mgo.Session) error {
    c := session.DB(your_DB).C(collection)
    err := c.Insert(insert)
    return err
}

func dbUpsert(collection string, selector bson.M, update bson.M, session *mgo.Session) (*mgo.ChangeInfo, error) {
    c := session.DB(your_DB).C(collection)
    info, err := c.Upsert(selector, update)
    return info, err
}

func dbFindOne(collection string, findBson bson.M, selectBson bson.M, session *mgo.Session) (map[string]interface{}, error) {
    c := session.DB(your_DB).C(collection)
    getMap := make(map[string]interface{})
    err := c.Find(findBson).Select(selectBson).One(&getMap)
    return getMap, err
}

func dbFindAll(collection string, findBson bson.M, selectBson bson.M, session *mgo.Session) (map[string]interface{}, error) {
    c := session.DB(your_DB).C(collection)
    getMap := make(map[string]interface{})
    err := c.Find(findBson).Select(selectBson).All(&getMap)
    return getMap, err
}

func dbUpdate(collection string, selector bson.M, update bson.M, session *mgo.Session) error {
    c := session.DB(your_DB).C(collection)
    setBson := bson.M{};
    setBson["$set"] = update;
    //
    updateError := c.Update(selector, setBson)
    //
    return updateError
}

func dbRemoveOne(collection string, selector bson.M, session *mgo.Session) error {
    c := session.DB(your_DB).C(collection)
    removeError := c.Remove(selector)
    return removeError
}

func dbRemoveAll(collection string, selector bson.M, session *mgo.Session) (*mgo.ChangeInfo, error) {
    c := session.DB(your_DB).C(collection)
    removeInfo, removeError := c.RemoveAll(selector)
    return removeInfo, removeError
}

Here's a sample query for find:

//FIND ONE:
employeeInfo, err := dbFindOne("employees", bson.M{"name": "john"}, bson.M{"salary": 1, "homeCity": 1}, mongo_session)

if err != nil {
    fmt.Println("Error getting employee info: ", err)
}else{
    //you can get the salary as an int:
    salary := employeeInfo["salary"].(int)

    //or get their homeCity as a string:
    homeCity := employeeInfo["homeCity"].(string)
}

This for instance finds the "salary" of employee named "john" in the collection "employees".

All the methods in the snippet work in almost the same exact way as dbFindOne() .

Hope this helps!