DBResolver

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

Quick Start

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"))

Automatic connection switching

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

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

Manual connection switching

// 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)

Transaction

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()

Load Balancing

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.

Connection Pool

DB.Use(
  dbresolver.Register(dbresolver.Config{ /* xxx */ }).
  SetConnMaxIdleTime(time.Hour).
  SetConnMaxLifetime(24 * time.Hour).
  SetMaxIdleConns(100).
  SetMaxOpenConns(200)
)