gorm multiple databases connection management - go

Question

I have a requirement where my application talks to different
databases . How do i manage connections in the gorm. Is there any
way gorm supports connection management for multiple database. or i
need to create map which holds all database connections.
if val, ok := selector.issure_db[issuer]; ok {
return val , nil;
} else {
var dbo *db.DB;
selector.mu.Lock()
dbo, err := db.NewDb(Config)
if err != nil {
boot.Logger(ctx).Fatal(err.Error())
}
selector.issure_db[issuer] = dbo;
selector.mu.Unlock()
return repo ,nil;
}
Is there is a better way to do this?

Answer 1

You can use the dbresolver plugin for GORM. It manages multiple sources and replicas and maintains an underlying connection pool for the group. You can even map models in your app to the correct database using the config.
Example from the docs:
import (
"gorm.io/gorm"
"gorm.io/plugin/dbresolver"
"gorm.io/driver/mysql"
)
db, err := gorm.Open(mysql.Open("db1_dsn"), &gorm.Config{})
db.Use(dbresolver.Register(dbresolver.Config{
// use `db2` as sources, `db3`, `db4` as replicas
Sources: []gorm.Dialector{mysql.Open("db2_dsn")},
Replicas: []gorm.Dialector{mysql.Open("db3_dsn"), mysql.Open("db4_dsn")},
// sources/replicas load balancing policy
Policy: dbresolver.RandomPolicy{},
}).Register(dbresolver.Config{
// use `db1` as sources (DB's default connection), `db5` as replicas for `User`, `Address`
Replicas: []gorm.Dialector{mysql.Open("db5_dsn")},
}, &User{}, &Address{}).Register(dbresolver.Config{
// use `db6`, `db7` as sources, `db8` as replicas for `orders`, `Product`
Sources: []gorm.Dialector{mysql.Open("db6_dsn"), mysql.Open("db7_dsn")},
Replicas: []gorm.Dialector{mysql.Open("db8_dsn")},
}, "orders", &Product{}, "secondary"))

Answer 2

You can create a package called database and write an init function in the init.go file which can create a DB object to connect with database for each database you have. And you can use this db object everywhere in the application which would enable connection pooling as well.
init.go
var db *gorm.DB
func init() {
var err error
dataSourceName := fmt.Sprintf("%s:%s#tcp(%s:%d)/%s?charset=utf8&parseTime=True&loc=Local", dbUser, dbPassword, dbHost, dbPort, dbName)
db, err = gorm.Open("mysql", dataSourceName)
db.DB().SetConnMaxLifetime(10 * time.Second)
db.DB().SetMaxIdleConns(10)
//initialise other db objects here
}
users.go
func getFirstUser() (user User) {
db.First(&user)
return
}
PS> This solution would be efficient if you have to connect to 1 or 2 database. If you need to connect to multiple databases at the same time, you should be using dbresolver plugin.
Old Answer
You can write a separate function which returns current database connection object every time you call the function.
func getDBConnection(dbUser, dbPassword, dbHost, dbName string) (db *gorm.DB, err error) {
dataSourceName := fmt.Sprintf("%s:%s#tcp(%s:%d)/%s?charset=utf8&parseTime=True&loc=Local", dbUser, dbPassword, dbHost, dbPort, dbName)
db, err = gorm.Open("mysql", dataSourceName)
db.DB().SetConnMaxLifetime(10 * time.Second)
return
}
And call defer db.Close() everytime after you call the getDBConnection function.
func getFirstUser() (user User) {
db, _ := getDBConnection()
defer db.Close()
db.First(&user)
return
}
This way your connections will be closed every time after you have executed the query.