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自定义回调处理是最常见的接口开发实现，开发中只需要对接口中的部分方法进行替换与修改，在驱动默认实现逻辑中注入自定义逻辑。所有的SQL语句执行必定会通过DoQuery或者DoExec或者 DoFilter接口，根据需求在自定义的驱动中实现并覆盖相关接口方法实现所需功能即可。

我们来看一个自定义回调处理的示例，现需要将所有执行的SQL语句记录到monitor表中，以方便于进行SQL审计。为简化示例编写，以下代码实现了一个自定义的MySQL驱动，该驱动继承于drivers下mysql模块内已经实现的Driver。

package driver

import (
	"context"

	"github.com/gogf/gf/contrib/drivers/mysql/v2"
	"github.com/gogf/gf/v2/database/gdb"
	"github.com/gogf/gf/v2/os/gtime"
)

// MyDriver is a custom database driver, which is used for testing only.
// For simplifying the unit testing case purpose, MyDriver struct inherits the mysql driver
// gdb.Driver and overwrites its functions DoQuery and DoExec.
// So if there's any sql execution, it goes through MyDriver.DoQuery/MyDriver.DoExec firstly
// and then gdb.Driver.DoQuery/gdb.Driver.DoExec.
// You can call it sql "HOOK" or "HiJack" as your will.
type MyDriver struct {
	*mysql.Driver
}

var (
	// customDriverName is my driver name, which is used for registering.
	customDriverName = "MyDriver"
)

func init() {
	// It here registers my custom driver in package initialization function "init".
	// You can later use this type in the database configuration.
	if err := gdb.Register(customDriverName, &MyDriver{}); err != nil {
		panic(err)
	}
}

// New creates and returns a database object for mysql.
// It implements the interface of gdb.Driver for extra database driver installation.
func (d *MyDriver) New(core *gdb.Core, node *gdb.ConfigNode) (gdb.DB, error) {
	return &MyDriver{
		&mysql.Driver{
			Core: core,
		},
	}, nil
}

// DoCommit commits current sql and arguments to underlying sql driver.
func (d *MyDriver) DoCommit(ctx context.Context, in gdb.DoCommitInput) (out gdb.DoCommitOutput, err error) {
	tsMilliStart := gtime.TimestampMilli()
	out, err = d.Core.DoCommit(ctx, in)
	tsMilliFinished := gtime.TimestampMilli()
	_, _ = in.Link.ExecContext(ctx,
		"INSERT INTO `monitor`(`sql`,`cost`,`time`,`error`) VALUES(?,?,?,?)",
		gdb.FormatSqlWithArgs(in.Sql, in.Args),
		tsMilliFinished-tsMilliStart,
		gtime.Now(),
		err,
	)
	return
}

我们看到，这里在包初始化方法init中使用了gdb.Register("MyDriver", &MyDriver{})来注册了了一个自定义名称的驱动。我们也可以通过gdb.Register("mysql", &MyDriver{})来覆盖已有的框架mysql驱动为自己的驱动。

驱动名称mysql为框架默认的DriverMysql驱动的名称。

由于这里我们使用了一个新的驱动名称MyDriver，因此在gdb配置中的type数据库类型时，需要填写该驱动名称。以下是一个使用配置的示例：

database:
  default:
  - link: "MyDriver:root:12345678@tcp(127.0.0.1:3306)/user"
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