I am trying to write a custom marshaler for a possibly nil
database type. It is structured in the exact same way as the sql.NullFloat64
type:
type NullFloat64 sql.NullFloat64
func (ni *NullFloat64) MarshalJSON() ([]byte, error) {
if !ni.Valid {
return []byte("null"), nil
}
return json.Marshal(ni.Float64)
}
Which is a part of larger struct
to be marshaled:
type Data struct {
X time.Time `json:"x"`
Y float32 `json:"y"`
Stderr NullFloat64 `json:"stderr"`
}
If I try to json.Marshal()
this struct
, it works correctly, creating:
{"x":"2017-01-12T23:36:12-05:00","y":4,"stderr":null}
I would like to omit the JSON key entirely if the value is null
. I added json:"stderr,omitempty"
to Data
.
Per the suggestion here, I tried just returning a nil
value from MarshalJSON
, but got:
json: error calling MarshalJSON for type common.NullFloat64: unexpected end of JSON input
I also tried updating Data
as:
type Data struct {
X time.Time `json:"x"`
Y float32 `json:"y"`
Stderr *NullFloat64 `json:"stderr,omitempty"`
}
And marshaling:
Data {
X: datetime,
Y: value,
Stderr: &stderr,
}
But got the same error when returning nil
from MarshalJSON
as before.
So, how can I implement MarshalJSON
for a custom type and omit the key when marshaling?
Thanks for the help!