如何在http处理程序中映射数据库？

I have a problem with mapping DB to HTTP Handler. So in Martini framework you can do like this:

// main.go
package main

func main() {
    db, err := gorm.Open("mysql", "<user>:<pass>@/mvc_demo")  
    m := martini.Classic()
    m.Map(&db)
    m.Run(":3000")
}

// controllers/index.go
package controllers

func IndexGET(w http.ResponseWriter, r *http.Request, *gorm.DB) { ... }

How to do the same with HttpRouter package, because when i parse the variable *gorm.DB, I get an error.