func getResourceField(v interface{}) (f *structs.Field, err error) {
var ok bool
if !structs.IsStruct(v) {
err = errors.New("not a struct")
} else if f, ok = structs.New(v).FieldOk("Id"); !ok {
err = errors.New("no 'Id' field")
} else if _, ok = f.Value().(int); !ok {
err = errors.New("Id field is not an int")
}
return
}
// Determine whether the struct's id will be omitted in json encoding.
func isIdOmitted(v interface{}) (bool, error) {
if structs.IsStruct(v) {
if f, err := getResourceField(v); err != nil {
return false, err
} else if jsonTag := f.Tag("json"); jsonTag == "" {
// No json tag means the id field won't be ommitted.
return false, nil
} else {
// getResourceField() ensures this is an int.
id := f.Value().(int)
// Json tags are comma separated. 'omitempty' means id == 0 -> id field
// not included in generated json. Also note spacing, like "id,
// omitempty" is significant and prevents a tag from taking effect so no
// need for trimming.
//
// See http://golang.org/pkg/encoding/json/#Marshal
for _, field := range strings.Split(jsonTag, ",") {
if field == "omitempty" && id == 0 {
return true, nil
}
}
}
} else {
ty := reflect.TypeOf(v)
switch ty.Kind() {
case reflect.Map:
if _, ok := v.(map[string]interface{}); !ok {
return false, errors.New("Invalid map")
} else {
return false, nil
}
case reflect.Ptr:
return isIdOmitted(reflect.Indirect(reflect.ValueOf(v)).Interface())
}
}
// Id field exists, no 'omitempty' tag so not omitted.
return false, nil
}