组件分享之后端组件——对其GORM增加多数据库支持功能的组件dbresolver
背景
近期正在探索前端、后端、系统端各类常用组件与工具，对其一些常见的组件进行再次整理一下，形成标准化组件专题，后续该专题将包含各类语言中的一些常用组件。欢迎大家进行持续关注。
组件基本信息
- 组件：dbresolver
- 开源协议：MIT license
- 官网：https://gorm.io/docs/dbresolver.html
内容
本节分享一个对其GORM增加多数据库支持功能的组件dbresolver，它支持以下功能：
- 多个来源，副本
- 读/写分离
- 基于工作表/结构的自动连接切换
- 手动连接切换
- 源/副本负载均衡
- 适用于原始 SQL
- 事务
具体使用如下：
代码语言：javascript复制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"))自动切换
代码语言：javascript复制// `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`手动连接开关
代码语言：javascript复制// 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)事务
代码语言：javascript复制// 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()负载平衡
GORM支持基于策略的源/副本负载均衡，策略是一个接口，实现如下接口：
代码语言：javascript复制type Policy interface {
Resolve([]gorm.ConnPool) gorm.ConnPool
}目前只执行RandomPolicy，如果没有指定策略，则为默认选项。
连接池
代码语言：javascript复制DB.Use(
dbresolver.Register(dbresolver.Config{ /* xxx */ }).
SetConnMaxIdleTime(time.Hour).
SetConnMaxLifetime(24 * time.Hour).
SetMaxIdleConns(100).
SetMaxOpenConns(200)
)
