引擎组负载策略

通过 xorm.NewEngineGroup 创建 EngineGroup 时，第三个参数为 policies，我们可以通过该参数来指定 Slave 访问的负载策略。如创建 EngineGroup 时未指定，则默认使用轮询的负载策略。

xorm 中内置五种负载策略，分别为随机访问负载策略、权重随机访问负载策略、轮询访问负载策略、权重轮询访问负载策略和最小连接数访问负载策略。开发者也可以通过实现 GroupPolicy 接口，来实现自定义负载策略。

1. 随机访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.RandomPolicy())
}

2. 权重随机访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    //此时设置的test1数据库和test2数据库的随机访问权重为2和3
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.WeightRandomPolicy([]int{2, 3}))
}

3. 轮询访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.RoundRobinPolicy())
}

4. 权重轮询访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    //此时设置的test1数据库和test2数据库的轮询访问权重为2和3
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.WeightRoundRobinPolicy([]int{2, 3}))
}

5. 最小连接数访问负载策略

import (
    _ "github.com/lib/pq"
    "github.com/xormplus/xorm"
)

var eg *xorm.EngineGroup

func main() {
    conns := []string{
        "postgres://postgres:root@localhost:5432/test?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test1?sslmode=disable;",
        "postgres://postgres:root@localhost:5432/test2?sslmode=disable",
    }

    var err error
    eg, err = xorm.NewEngineGroup("postgres", conns, xorm.LeastConnPolicy())
}

6. 自定义负载策略

你也可以通过实现 GroupPolicy 接口来实现自定义负载策略。

type GroupPolicy interface {
    Slave(*EngineGroup) *Engine
}

xorm 支持将一个 struct 映射为数据库中对应的一张表。名称映射规则主要负责结构体名称到表名和结构体 field 到表字段的名称映射。由 core.IMapper 接口的实现者来管理，xorm内置了三种IMa ...