Dynamically insert multiple documents using mgo golang mongodb

Question

How can I insert an array of documents into MongoDB with mgo library using only a single DB call as in db.collection.insert()?

I have the following Transaction structure:

    type Transaction struct {
    Brand         string `json:"brand"`
    Name          string `json:"name"`
    Plu           string `json:"plu"`
    Price         string `json:"price"`
  }

From a POST request I will recieve an array of these structures. I want to insert them into MongoDB as individual documents but using a single DB call as explained in db.collection.insert()

I tried using c.Insert of mgo

The following is the code snippet:

  func insertTransaction(c *gin.Context) {
    var transactions []Transaction
    err := c.BindJSON(&transactions)
    if err != nil {
        c.AbortWithStatusJSON(http.StatusBadRequest, map[string]string{"error":"invalid JSON"})
        return
    }
    err = InsertTransactons(transactions)
    if err != nil {
        c.AbortWithStatusJSON(http.StatusInternalServerError, &map[string](interface{}){
            "status":  "error",
            "code":    "500",
            "message": "Internal server error",
            "error": err,
        })
        return
    }
    c.JSON(http.StatusCreated, &map[string](interface{}){
        "status":  "success",
        "code":    "0",
        "message": "created",
    })
  }


  func InsertTransactons(u []Transaction) error {
    s := GetSession()
    defer s.Close()
    c := s.DB(DB).C(TransactionColl)
    err := c.Insert(u...)
    if err != nil {
        return err
    }
    return nil
  }

But as I compile and run the code, I get the following error:

go/database.go:34:17: cannot use u (type *[]Transaction) as type []interface {} in argument to c.Insert

As the error says you are trying to insert pointer to Transaction slice. Though Collection.Insert() takes []interface{} not *[]interface{} — Himanshu
– Himanshu, Commented Feb 18, 2018 at 9:21

vedhavyas · Accepted Answer · 2018-02-18 09:23:37Z

12

You cannot pass []*Transaction as []interface{}. You need to convert each Transaction to inferface{} to change its memory layout.

var ui []interface{}
for _, t := range u{
    ui = append(ui, t)
}

Pass ui to c.Insert instead

answered Feb 18, 2018 at 9:23

vedhavyas

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3 Comments

Nidhin David Over a year ago

Thanks dude..It worked! I wish if there was no need for a range

uberrebu Over a year ago

when answers do not use the same variable/constant names as questions, it becomes VERY confusing for users trying to make use of the answers later..where did ui come from?

ᐅdevrimbaris Over a year ago

@uberrebu "ui" is just an array of interfaces defined to include all the items converted to interface. You can rename it to anything.

Himanshu · Accepted Answer · 2018-02-18 16:46:28Z

3

Create slice of interface for document structs by appending and then inserting data using Bulk insert which takes variable arguments.

type Bulk struct {
    // contains filtered or unexported fields
}
func (b *Bulk) Insert(docs ...interface{})

For inserting documents in Bulk

const INSERT_COUNT int = 10000

type User struct {
    Id    bson.ObjectId `bson:"_id,omitempty" json:"_id"`
    Email string        `bson:"email" json:"email"`
}

func (self *User) Init() {
    self.Id = bson.NewObjectId()
}

Call Bulk() function on collection returned from db connection. Bulk() function returns pointer to *Bulk.

bulk := dbs.Clone().DB("").C("users").Bulk()
bulk.Insert(users...)

Assign it to variable which will be used to call Insert() method using Bulk pointer receiver.

func main(){
    // Database
    dbs, err := mgo.Dial("mongodb://localhost/")
    if err != nil {
        panic(err)
    }
    // Collections
    uc := dbs.Clone().DB("").C("users")
    defer dbs.Clone().DB("").Session.Close()
    for n := 0; n < b.N; n++ {
        count := INSERT_COUNT
        users := make([]interface{}, count)
        for i := 0; i < count; i++ {
            loop_user := User{}
            loop_user.Init()
            loop_user.Email = fmt.Sprintf("report-%[email protected]", i)
            users[i] = loop_user
        }
        bulk := uc.Bulk()
        bulk.Unordered()
        bulk.Insert(users...)
        _, bulkErr := bulk.Run()
        if bulkErr != nil {
            panic(err)
        }
    }
}

edited Feb 18, 2018 at 16:46

answered Feb 18, 2018 at 9:19

Himanshu

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1 Comment

Nidhin David Over a year ago

Thanks for this answer. Actually I wouldn't wanted to use bulk update as insert already supports multiple documents. Anyway I will refer this for bulk update

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