How correctly use UUID4 in Golang application? - go

Question

I am new in Golang and need some help! I have several questions.
In PostgreSQL database I have table called surveys.
CREATE TABLE SURVEYS(
SURVEY_ID UUID PRIMARY KEY NOT NULL DEFAULT uuid_generate_v4(),
SURVEY_NAME VARCHAR NOT NULL,
SURVEY_DESCRIPTION TEXT,
START_PERIOD TIMESTAMP,
END_PERIOD TIMESTAMP
);
As you can see SURVEY_ID column is PRIMARY KEY and it's type is UUID4.
In Golang application I create such struct to this table:
type Survey struct {
ID string `json:"survey_id"`
Name string `json:"survey_name"`
Description utils.NullString `json:"survey_description"`
StartPeriod utils.NullTime `json:"start_period"`
EndPeriod utils.NullTime `json:"end_period"`
}
As you can see type of ID field is string. Is it correct? I am not sure that it's best practice.
My second question about strange result which I have when make GET request to specific survey by it's ID.
For example when I make such request:
http://localhost:8000/api/survey/0cf1cf18-d5fd-474e-a8be-754fbdc89720
As response I have this:
{
"survey_id": "0cf1cf18-d5fd-474e-a8be-754fbdc89720",
"survey_name": "NAME",
"survey_description": {
"String": "DESCRIPTION",
"Valid": true
},
"start_period": {
"Time": "2019-01-01T00:00:00Z",
"Valid": false
},
"end_period": {
"Time": "0001-01-01T00:00:00Z",
"Valid": false
}
}
As you can see something wrong with last 3 field: survey_description, start_period and end_period. I want to see key and value in one line. For example as here:
{
"survey_id": "0cf1cf18-d5fd-474e-a8be-754fbdc89720",
"survey_name": "NAME",
"survey_description": "DESCRIPTION",
"start_period": "2019-01-01 00:00:00",
"end_period": null
}
Where exactly I make mistake in my code?
utils.go:
package utils
import (
"database/sql"
"encoding/json"
"fmt"
"github.com/lib/pq"
"time"
)
// NullTime is an alias for pq.NullTime data type.
type NullTime struct {
pq.NullTime
}
// MarshalJSON for NullTime.
func (nt *NullTime) MarshalJSON() ([]byte, error) {
if !nt.Valid {
return []byte("null"), nil
}
val := fmt.Sprintf("\"%s\"", nt.Time.Format(time.RFC3339))
return []byte(val), nil
}
// UnmarshalJSON for NullTime.
func (nt *NullTime) UnmarshalJSON(b []byte) error {
err := json.Unmarshal(b, &nt.Time)
nt.Valid = err == nil
return err
}
// NullInt64 is an alias for sql.NullInt64 data type.
type NullInt64 struct {
sql.NullInt64
}
// MarshalJSON for NullInt64.
func (ni *NullInt64) MarshalJSON() ([]byte, error) {
if !ni.Valid {
return []byte("null"), nil
}
return json.Marshal(ni.Int64)
}
// UnmarshalJSON for NullInt64.
func (ni *NullInt64) UnmarshalJSON(b []byte) error {
err := json.Unmarshal(b, &ni.Int64)
ni.Valid = err == nil
return err
}
// NullString is an alias for sql.NullString data type.
type NullString struct {
sql.NullString
}
// MarshalJSON for NullString.
func (ns *NullString) MarshalJSON() ([]byte, error) {
if !ns.Valid {
return []byte("null"), nil
}
return json.Marshal(ns.String)
}
// UnmarshalJSON for NullString.
func (ns *NullString) UnmarshalJSON(b []byte) error {
err := json.Unmarshal(b, &ns.String)
ns.Valid = err == nil
return err
}
routes.go:
router.HandleFunc("/api/survey/{survey_id:[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-4[a-fA-F0-9]{3}-[8|9|aA|bB][a-fA-F0-9]{3}-[a-fA-F0-9]{12}}", controllers.GetSurvey).Methods("GET")
controllers/survey.go:
var GetSurvey = func(responseWriter http.ResponseWriter, request *http.Request) {
// Initialize variables.
survey := models.Survey{}
var err error
vars := mux.Vars(request)
// Execute SQL statement.
err = database.DB.QueryRow("SELECT * FROM surveys WHERE survey_id = $1;", vars["survey_id"]).Scan(&survey.ID, &survey.Name, &survey.Description, &survey.StartPeriod, &survey.EndPeriod)
// Shape the response depending on the result of the previous command.
if err != nil {
log.Println(err)
switch err {
case sql.ErrNoRows:
utils.ResponseWithError(responseWriter, http.StatusNotFound, "The entry not found.")
default:
utils.ResponseWithError(responseWriter, http.StatusInternalServerError, err.Error())
}
return
}
utils.Response(responseWriter, http.StatusOK, survey)
}

Answer 1

Well, finally I found the result.
I changed the struct for the table:
type Survey struct {
ID string `json:"survey_id"`
Name string `json:"survey_name"`
Description *string `json:"survey_description", sql:"index"`
StartPeriod *time.Time `json:"start_period", sql:"index"`
EndPeriod *time.Time `json:"end_period", sql:"index"`
}

Answer 2

I don't see any issue with using a string for a UUID.
As for the MarshalJSON not working, I think I know what's going on. Your null types don't implement MarshalJSON, only the pointers to them. The fix would be to either change the function to use a non-pointer receiver, or make the fields pointers in your struct.
func (ns *NullString) MarshalJSON() ([]byte, error)
If you did make them pointers, then you could just keep them like that, since they're nullable.