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

type student struct {     FirstName  interface{} `json:"first_name"`     MiddleName interface{} `json:"middle_name"`     LastName   interface{} `json:"last_name"` } 

The application I am sending my data expect a null instead of an empty string if value is not available for that specific field.

Is this the correct approach or can someone please point me to something better than this.

Answer 1

In json package documentation :

Pointer values encode as the value pointed to. A nil pointer encodes as the null JSON object.

So you can store a pointer to a string which will be encoded as a string if not nil and will be encoded as "null" if nil

type student struct {   FirstName  *string `json:"first_name"`   MiddleName *string `json:"middle_name"`   LastName   *string `json:"last_name"` } 

Answer 2

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.