I am struggling with deserializing a integer into a string struct field. The struct field is a string and is expected to be assignable from users of my library. That's why I want it to be a string, since for the purpose of writing it to the database I actually don't care about the value inside. The users can supply text, but some just assign integers.
Consider this struct:
type Test struct {
Foo string
}
Sometimes I end up with a JSON value that is valid but won't deserialize into the struct due to the Foo field being a integer instead of a string:
{ "foo": "1" } // works
{ "foo": 1 } // doesn't
json.Unmarshal will blow up with the following error:
json: cannot unmarshal number into Go struct field test.Foo of type string
See the reproduction: https://play.golang.org/p/4Qau3umaVm
Now in every other JSON library (in other languages) I have worked in so far, if the target field is a string and you get a integer the deserializer will usually just wrap the int in a string and be done with it. Can this be achieved in Go?
Since I can't really control how the data comes in I need to make json.Unmarshal unsensitive to this - the other solution would be to define Foo as interface{} which needlessly complicates my code with type assertions etc..
Any ideas on how to do this? I basically need the inverse of json:",string"
To handle big structs you can use embedding.
Updated to not discard possibly previously set field values.
func (t *T) UnmarshalJSON(d []byte) error {
type T2 T // create new type with same structure as T but without its method set!
x := struct{
T2 // embed
Foo json.Number `json:"foo"`
}{T2: T2(*t)} // don't forget this, if you do and 't' already has some fields set you would lose them
if err := json.Unmarshal(d, &x); err != nil {
return err
}
*t = T(x.T2)
t.Foo = x.Foo.String()
return nil
}