Assigning null to JSON fields instead of empty strings

Question

Since empty string is the zero/default value for Go string, I decided to define all such fields as interface{} instead. for example

Answer 1

Another way actually is a workaround with using the MarhshalJSON and UnmarshalJSON interface method offered by the json lib of golang. The code is as below:

type MyType string
type MyStruct struct {
    A MyType `json:"my_type"`
}

func (c MyType) MarshalJSON() ([]byte, error) {
    var buf bytes.Buffer
    if len(string(c)) == 0 {
        buf.WriteString(`null`)
    } else {
        buf.WriteString(`"` + string(c) + `"`)   // add double quation mark as json format required
    }
    return buf.Bytes(), nil
}

func (c *MyType)UnmarshalJSON(in []byte) error {
    str := string(in)
    if str == `null` {
        *c = ""
        return nil
    }
    res := MyType(str)
    if len(res) >= 2 {
        res = res[1:len(res)-1]     // remove the wrapped qutation
    }
    *c = res
    return nil
}

then when using json.Marshal, the MyType value will be marshaled as null.