像Int64和String这样的围棋类型不能存储空值，
所以我发现我可以用sql.NullInt64和sql.NullString来做这个.
But when I use these in a Struct,
and generate JSON from the Struct with the json package,
then the format is different to when I use regular Int64 and String types.
JSON有一个额外的级别，因为sql.Null*也是一个Struct.
Is there a good workaround for this, or should I not use NULLs in my SQL database?
Types like sql.NullInt64 do not implement any special handling for JSON marshaling or unmarshaling, so the default rules apply. Since the type is a struct, it gets marshalled as an object with its fields as attributes.
One way to work around this is to create your own type that implements the json.Marshaller / json.Unmarshaler interfaces. By embedding the sql.NullInt64 type, we get the SQL methods for free. Something like this:
type JsonNullInt64 struct {
sql.NullInt64
}
func (v JsonNullInt64) MarshalJSON() ([]byte, error) {
if v.Valid {
return json.Marshal(v.Int64)
} else {
return json.Marshal(nil)
}
}
func (v *JsonNullInt64) UnmarshalJSON(data []byte) error {
// Unmarshalling into a pointer will let us detect null
var x *int64
if err := json.Unmarshal(data, &x); err != nil {
return err
}
if x != nil {
v.Valid = true
v.Int64 = *x
} else {
v.Valid = false
}
return nil
}
If you use this type in place of sql.NullInt64, it should be encoded as you expect.
你可以在这里测试这个例子:http://play.golang.org/p/zFESxLcd-c