func (context *Context) GetDB() *gorm.DB {
	if context.DB != nil {
		return context.DB
	}
	return context.Config.DB
}
GetDB get db from current context
package qor
import (
	"net/http"
	"github.com/jinzhu/gorm"
)
type CurrentUser interface {
	DisplayName() string
}
type Context struct {
	Request     *http.Request
	Writer      http.ResponseWriter
	CurrentUser CurrentUser
	Roles       []string
	ResourceID  string
	DB          *gorm.DB
	Config      *Config
	Errors
}
func (context *Context) Clone() *Context {
	var clone = *context
	return &clone
}