How to insert multiple data at once

I know that Insert multiple data at once more efficiency:

INSERT INTO test(n1, n2, n3) 
VALUES(v1, v2, v3),(v4, v5, v6),(v7, v8, v9);

How to do that in golang?

data := []map[string]string{
   {"v1":"1", "v2":"1", "v3":"1"},
   {"v1":"2", "v2":"2", "v3":"2"},
   {"v1":"3", "v2":"3", "v3":"3"},
}
//I do not want to do it
for _, v := range data {
    sqlStr := "INSERT INTO test(n1, n2, n3) VALUES(?, ?, ?)"
    stmt, _ := db.Prepare(sqlStr)
    res, _ := stmt.Exec(v["v1"], v["v2"], v["v3"])
}

Use string splice, but it's not good. db.Prepare more safer, right?

sqlStr := "INSERT INTO test(n1, n2, n3) VALUES"
for k, v := range data {
    if k == 0 {
        sqlStr += fmt.Sprintf("(%v, %v, %v)", v["v1"], v["v2"], v["v3"])
    } else {
        sqlStr += fmt.Sprintf(",(%v, %v, %v)", v["v1"], v["v2"], v["v3"])
    } 
}
res, _ := db.Exec(sqlStr)

I need a function safer and efficient insert mulitple data at once.

why not something like this? (writing here without testing so there might be syntax errors):

sqlStr := "INSERT INTO test(n1, n2, n3) VALUES "
vals := []interface{}{}

for _, row := range data {
	sqlStr += "(?, ?, ?),"
	vals = append(vals, row["v1"], row["v2"], row["v3"])
}
//trim the last ,
sqlStr = sqlStr[0:len(sqlStr)-1]
//prepare the statement
stmt, _ := db.Prepare(sqlStr)

//format all vals at once
res, _ := stmt.Exec(vals...)

For Postgres lib pq supports bulk inserts: https://godoc.org/github.com/lib/pq#hdr-Bulk_imports

But same can be achieved through below code but where it is really helpful is when one tries to perform bulk conditional update (change the query accordingly).

For performing similar bulk inserts for Postgres, you can use the following function.

// ReplaceSQL replaces the instance occurrence of any string pattern with an increasing $n based sequence
func ReplaceSQL(old, searchPattern string) string {
   tmpCount := strings.Count(old, searchPattern)
   for m := 1; m <= tmpCount; m++ {
	  old = strings.Replace(old, searchPattern, "$"+strconv.Itoa(m), 1)
   }
   return old
}

So above sample becomes

sqlStr := "INSERT INTO test(n1, n2, n3) VALUES "
vals := []interface{}{}

for _, row := range data {
   sqlStr += "(?, ?, ?),"
   vals = append(vals, row["v1"], row["v2"], row["v3"])
}

//trim the last ,
sqlStr = strings.TrimSuffix(sqlStr, ",")

//Replacing ? with $n for postgres
sqlStr = ReplaceSQL(sqlStr, "?")

//prepare the statement
stmt, _ := db.Prepare(sqlStr)

//format all vals at once
res, _ := stmt.Exec(vals...)

Gorm V2 (released on 30th August 2020) now supports batch insert query.

// Pass slice data to method Create, GORM will generate a single SQL statement
// to insert all the data and backfill primary key values,
// hook methods will be invoked too.

var users = []User{{Name: "jinzhu1"}, {Name: "jinzhu2"}, {Name: "jinzhu3"}}
DB.Create(&users)

for _, user := range users {
  user.ID // 1,2,3
}

For more details refer to the official documentation here: https://gorm.io/docs/create.html.

If you enable multi statements , then you can execute multiple statement at once.
With that , you should be able to handle multiple inserts.

https://github.com/go-sql-driver/mysql#multistatements

After extensive research this worked for me:

var values []interface{}
for _, scope := range scopes {
	values = append(values, scope.ID, scope.Code, scope.Description)
}
sqlStr := `INSERT INTO scopes (application_id, scope, description) VALUES %s`
sqlStr = setupBindVars(sqlStr, "(?, ?, ?)", len(scopes))

_, err = s.db.ExecContext(ctx, sqlStr, values...)

// helper function to replace ? with the right number of sets of bind vars

func setupBindVars(stmt, bindVars string, len int) string {
	bindVars += ","
	stmt = fmt.Sprintf(stmt, strings.Repeat(bindVars, len))
	return strings.TrimSuffix(stmt, ",")
}

From https://gorm.io/docs/create.html#Batch-Insert

Code sample:

var users = []User{{Name: "jinzhu1"}, {Name: "jinzhu2"}, {Name: "jinzhu3"}}
DB.Create(&users)

this is an efficient way to do transition which will do network call only after commit.

func insert(requestObj []models.User) (bool, error) {
	tx := db.Begin()
	defer func() {
		if r := recover(); r != nil {
			tx.Rollback()
		}
	}()

	for _, obj := range requestObj {
		if err := tx.Create(&obj).Error; err != nil {
			logging.AppLogger.Errorf("Failed to create user")
			tx.Rollback()
			return false, err
		}
	}
	err := tx.Commit().Error
	if err != nil {
		return false, err
	}
	return true, nil
}

I ended up with this, after combining the feedback on posted answers:

const insertQuery := "INSERT INTO test(n1, n2, n3) VALUES "
const row = "(?, ?, ?)"

var inserts []string 
vars vals []interface{}

for _, row := range data {
    inserts = append(inserts, row)
    vals = append(vals, row["v1"], row["v2"], row["v3"])
}
sqlStr := insertQuery + strings.Join(inserts, ",")

//prepare the statement
stmt, _ := db.Prepare(sqlStr)

//close stmt after use
defer stmt.Close()

//format all vals at once
res, _ := stmt.Exec(vals...)