DBResolver
原文：https://gorm.io/docs/dbresolver.html
DBResolver adds multiple databases support to GORM, the following features are supported:
DBResolver为GORM提供了多个数据库支持，以下是支持的功能：
- Multiple sources, replicas
- 多数据源、副本
- Read/Write Splitting
- 读写分离
- Automatic connection switching based on the working table/struct
- 根据工作表/结构自动切换连接
- Manual connection switching
- 手动切换连接
- Sources/Replicas load balancing
- 数据源/副本负载均衡
- Works for RAW SQL
- 支持RAW SQL
- Transaction
- 事务
https://github.com/go-gorm/dbresolver
用法 Usage
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| 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{
// 使用 `db2` 作为数据源，`db3`、`db4` 作为副本 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")},
// 数据源/副本负载均衡策略 sources/replicas load balancing policy
Policy: dbresolver.RandomPolicy{},
// 在日志中打印数据源/副本模式 print sources/replicas mode in logger
TraceResolverMode: true,
}).Register(dbresolver.Config{
// 使用 `db1` 作为默认连接（数据库的默认连接），`db5` 用于 `User`、`Address` 的副本 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{
// 使用 `db6`、`db7` 作为数据源，`db8` 作为 `orders`、`Product` 的副本 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"))
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自动连接切换 Automatic connection switching
DBResolver will automatically switch connection based on the working table/struct
DBResolver 根据正在工作的表/结构自动切换连接。
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 (excepts SELECT... FOR UPDATE), for example:
对于RAW SQL，DBResolver将从SQL中提取表名以匹配解析器，除非SQL以SELECT开头（除了SELECT... FOR UPDATE），例如：
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| // `User` 解析器示例 `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`
// 全局解析器示例 Global Resolver Examples
db.Find(&Pet{}) // replicas `db3`/`db4`
db.Save(&Pet{}) // sources `db2`
// Orders 解析器示例 Orders Resolver Examples
db.Find(&Order{}) // replicas `db8`
db.Table("orders").Find(&Report{}) // replicas `db8`
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读写分离 Read/Write Splitting
Read/Write splitting with DBResolver based on the current used GORM callbacks.
基于当前使用的GORM回调进行读写分离的DBResolver。
For Query, Row callback, will use replicas unless Write mode specified
对于Query、Row回调，将使用副本，除非指定了Write模式。
For Raw callback, statements are considered read-only and will use replicas if the SQL starts with SELECT
对于Raw回调，语句被认为是只读的，如果SQL以SELECT开头，则将使用副本。
手动连接切换 Manual connection switching
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| // 使用写模式：从数据源 `db1` 读取用户 Use Write Mode: read user from sources `db1`
db.Clauses(dbresolver.Write).First(&user)
// 指定解析器：从 `secondary` 的副本中读取用户：db8 Specify Resolver: read user from `secondary`'s replicas: db8
db.Clauses(dbresolver.Use("secondary")).First(&user)
// 指定解析器和写模式：从 `secondary` 的数据源中读取用户：db6 或 db7 Specify Resolver and Write Mode: read user from `secondary`'s sources: db6 or db7
db.Clauses(dbresolver.Use("secondary"), dbresolver.Write).First(&user)
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事务 Transaction
When using transaction, DBResolver will keep using the transaction and won’t switch to sources/replicas based on configuration
在使用事务时，DBResolver将保持使用事务并不会根据配置切换到数据源/副本。
But you can specifies which DB to use before starting a transaction, for example:
但是，您可以在开始事务之前指定要使用的数据库，例如：
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| // 根据默认副本数据库启动事务 Start transaction based on default replicas db
tx := DB.Clauses(dbresolver.Read).Begin()
// 根据默认数据源数据库启动事务 Start transaction based on default sources db
tx := DB.Clauses(dbresolver.Write).Begin()
// 根据 `secondary` 的数据源启动事务 Start transaction based on `secondary`'s sources
tx := DB.Clauses(dbresolver.Use("secondary"), dbresolver.Write).Begin()
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负载均衡 Load Balancing
GORM supports load balancing sources/replicas based on policy, the policy should be a struct implements following interface:
GORM支持基于策略的负载均衡数据源/副本，策略应实现以下接口：
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| type Policy interface {
Resolve([]gorm.ConnPool) gorm.ConnPool
}
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Currently only the RandomPolicy implemented and it is the default option if no other policy specified.
目前只有实现了RandomPolicy的策略，如果没有指定其他策略，则为默认选项。
连接池 Connection Pool
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| db.Use(
dbresolver.Register(dbresolver.Config{ /* xxx */ }).
SetConnMaxIdleTime(time.Hour).
SetConnMaxLifetime(24 * time.Hour).
SetMaxIdleConns(100).
SetMaxOpenConns(200)
)
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