DBResolver adds multiple databases support to GORM, the following features are supported:
- Multiple sources, replicas
- Read/Write Splitting
- Automatic connection switching based on the working table/struct
- Manual connection switching
- Sources/Replicas load balancing
- Works for RAW SQL
- Transaction
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{},
// print sources/replicas mode in logger
ResolverModeReplica: true,
}).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"))DBResolver will automatically switch connections based on the working table/struct
For RAW SQL, DBResolver will extract the table name from the SQL to match the resolver, and will use sources unless the SQL begins with SELECT, for example:
// `User` Resolver Examples
DB.Table("users").Rows() // replicas `db5`
DB.Model(&User{}).Find(&AdvancedUser{}) // replicas `db5`
DB.Exec("update users set name = ?", "jinzhu") // sources `db1`
DB.Raw("select name from users").Row().Scan(&name) // replicas `db5`
DB.Create(&user) // sources `db1`
DB.Delete(&User{}, "name = ?", "jinzhu") // sources `db1`
DB.Table("users").Update("name", "jinzhu") // sources `db1`
// Global Resolver Examples
DB.Find(&Pet{}) // replicas `db3`/`db4`
DB.Save(&Pet{}) // sources `db2`
// Orders Resolver Examples
DB.Find(&Order{}) // replicas `db8`
DB.Table("orders").Find(&Report{}) // replicas `db8`Read/Write splitting with DBResolver based on the current using GORM callback.
For Query, Row callback, will use replicas unless Write mode specified
For Raw callback, statements are considered read-only and will use replicas if the SQL starts with SELECT
// Use Write Mode: read user from sources `db1`
DB.Clauses(dbresolver.Write).First(&user)
// Specify Resolver: read user from `secondary`'s replicas: db8
DB.Clauses(dbresolver.Use("secondary")).First(&user)
// Specify Resolver and Write Mode: read user from `secondary`'s sources: db6 or db7
DB.Clauses(dbresolver.Use("secondary"), dbresolver.Write).First(&user)When using transaction, DBResolver will keep using the transaction and won't switch to sources/replicas based on configuration
But you can specifies which DB to use before starting a transaction, for example:
// Start transaction based on default replicas db
tx := DB.Clauses(dbresolver.Read).Begin()
// Start transaction based on default sources db
tx := DB.Clauses(dbresolver.Write).Begin()
// Start transaction based on `secondary`'s sources
tx := DB.Clauses(dbresolver.Use("secondary"), dbresolver.Write).Begin()GORM supports load balancing sources/replicas based on policy, the policy is an interface implements following interface:
type Policy interface {
Resolve([]gorm.ConnPool) gorm.ConnPool
}Currently only the RandomPolicy implemented and it is the default option if no policy specified.
DB.Use(
dbresolver.Register(dbresolver.Config{ /* xxx */ }).
SetConnMaxIdleTime(time.Hour).
SetConnMaxLifetime(24 * time.Hour).
SetMaxIdleConns(100).
SetMaxOpenConns(200)
)