golang null.String decoding not working correctly - sql

Question

Trying to fix this problem i'm having with my api im building.
db:
DROP TABLE IF EXISTS contacts CASCADE;
CREATE TABLE IF NOT EXISTS contacts (
uuid UUID UNIQUE PRIMARY KEY,
first_name varchar(150),
);
DROP TABLE IF EXISTS workorders CASCADE;
CREATE TABLE IF NOT EXISTS workorders (
uuid UUID UNIQUE PRIMARY KEY,
work_date timestamp WITH time zone,
requested_by UUID REFERENCES contacts (uuid) ON UPDATE CASCADE ON DELETE CASCADE,
);
struct:
https://gopkg.in/guregu/null.v3
type WorkorderNew struct {
UUID string `json:"uuid"`
WorkDate null.Time `json:"work_date"`
RequestedBy null.String `json:"requested_by"`
}
api code:
workorder := &models.WorkorderNew{}
if err := json.NewDecoder(r.Body).Decode(workorder); err != nil {
log.Println("decoding fail", err)
}
// fmt.Println(NewUUID())
u2, err := uuid.NewV4()
if err != nil {
log.Fatalf("failed to generate UUID: %v", err)
}
q := `
INSERT
INTO workorders
(uuid,
work_date,
requested_by
)
VALUES
($1,$2,$3)
RETURNING uuid;`
statement, err := global.DB.Prepare(q)
global.CheckDbErr(err)
fmt.Println("requested by", workorder.RequestedBy)
lastInsertID := ""
err = statement.QueryRow(
u2,
workorder.WorkDate,
workorder.RequestedBy,
).Scan(&lastInsertID)
global.CheckDbErr(err)
json.NewEncoder(w).Encode(lastInsertID)
When I send an API request with null as the value it works as expected
but when i try to send a "" as the value for the null.String or the null.Time it fails
works:
{
"work_date":"2016-12-16T19:00:00Z",
"requested_by":null
}
not working:
{
"work_date":"2016-12-16T19:00:00Z",
"requested_by":""
}
Basically when i call the QueryRow and save to database the workorder.RequestedBy value should be a null and not the "" value im getting
thanks

Answer 1

If you want to treat empty strings as nulls you have at least two options.
"Extend" null.String:
type MyNullString struct {
null.String
}
func (ns *MyNullString) UnmarshalJSON(data []byte) error {
if string(data) == `""` {
ns.Valid = false
return nil
}
ns.String.UnmarshalJSON(data)
}
Or use NULLIF in the query:
INSERT INTO workorders (
uuid
, work_date
, requested_by
) VALUES (
$1
, $2
, NULLIF($3, '')
)
RETURNING uuid
Update:
To extend the null.Time you have to understand that the type of null.Time.Time is a struct. The builtin len function works on slices, arrays, pointers to arrays, maps, channels, and strings. Not structs. So in this case you can check the data argument, which is a byte slice, by converting it to a string and comparing it to a string that contains an empty string, i.e. it has two double quotes and nothing else.
type MyNullTime struct {
null.Time
}
func (ns *MyNullTime) UnmarshalJSON(data []byte) error {
if string(data) == `""` {
ns.Valid = false
return nil
}
return ns.Time.UnmarshalJSON(data)
}