DataAccess负责判断和选择具体的工厂会不会更好点

[RoachZhangq]

type DataAccess struct {
db string
}

func (d *DataAccess) createFactory(db string) Ifactory {
if d == nil {
return nil
}

var f Ifactory

if db == "sqlserver" {
	f = new(SqlServerFactory)
} else if db == "access" {
	f = new(AccessFactory)
}
return f

}