Go wrapping json.Number with sql.NullFloat64 - json

Question

I'm working with an API that has json values that can be a number or string and can sometimes be an empty string. For example:
[
{
"Description": "Doorknob",
"Amount": 3.25
},
{
"Description": "Light bulb",
"Amount": "4.70"
},
{
"Description": "Screwdriver",
"Amount": ""
}
]
I've learned I can use json.Number to deal with cases where the value can be a number or a string. But how do I deal with the cases where it's an empty string?
I need to insert these values into a postgres database so I'd like cases where it's an empty string to show as null and I'm thinking sql.NullFloat64 would be best suited to handle it.
Here's a function I'm using that works on the first 2 cases (Doorknob and Light bulb), but fails to unmarshal the last ("Screwdriver").
Here is an unmarshaling function I'm trying to use, but I can't figure out why it's not working:
type NullNumber struct{ sql.NullFloat64 }
func (nn *NullNumber) UnmarshalJSON(data []byte) error {
var x *json.Number
if err := json.Unmarshal(data, &x); err != nil {
return err
}
if len(*x) == 0 {
nn.Valid = false // This doesn't seem to be working. Why?
}
this, err := x.Float64()
if err != nil {
return err
}
nn.Valid = true
nn.Float64 = this
return nil
}
Is this a case where I should be using an open interface for the amount?
Any help is very appreciated.
playground: https://play.golang.org/p/QYQRq94OtV3

Answer 1

You're almost there! json.Unmarshal call errors when a json.Number is given an empty string.
Add this check beforehand:
// edge case: json.Number is given an empty string
if bytes.Equal(data, []byte(`""`)) {
nn.Valid = false
return nil
}
https://play.golang.org/p/ILxC8tjYI_G