将protobuf消息转换为struct后添加了一些奇怪的字段？

I want to have an API to save a User. Here is my user message:

message User {
    int32 uid = 1;
    string username = 2;
    string password = 3;
}

And I use protoc-gen-go to convert it to go struct. I found some strange fields was added(XXX_NoUnkeyedLiteral, XXX_unrecognized).

type User struct {
    Uid                  int32    `protobuf:"varint,1,opt,name=uid,proto3" json:"uid,omitempty"`
    Username             string   `protobuf:"bytes,2,opt,name=username,proto3" json:"username,omitempty"`
    Password             string   `protobuf:"bytes,3,opt,name=password,proto3" json:"password,omitempty"`
    XXX_NoUnkeyedLiteral struct{} `json:"-"`
    XXX_unrecognized     []byte   `json:"-"`
    XXX_sizecache        int32    `json:"-"`
}

I can't save it to MySQL due to those fields because my MySQL table doesn't have those fields. anyone good advice? I have to create another struct to convert MySQL table to protobuf Message?