I am fetching a JSON array from PostgreSQL, and I would like to read it into a map. I am able to Unmarshal the values into a []string
slice, but what I actually want is a map[string]bool
.
I've written a custom type for the column with a Scan interface that converts the JSON array into a slice of strings first, then reads each string into the custom map type as keys.
type custMap map[string]bool
func (m *custMap) Scan(src interface{}) error {
b, ok := src.([]byte)
if !ok {
return error(errors.New("Error Scanning Array"))
}
s := make([]string, 0)
json.Unmarshal(b, &s)
for _, v := range s {
(*m)[v] = true
}
return nil
}
type data struct {
vals custMap `json: "vals"`
}
The query I am trying to scan returns a row with a column vals which is a JSON array: ["some", "arr", "vals"]
, where the custom type is used like so:
var d models.data
sqlDB.QueryRow().Scan(&d.vals)
My expected output is a struct with the following shape
{ vals: map[string]bool { "some": true, "arr": true, "vals": true }
This compiles fine, but my code panics with "assignment to entry in nil map"
How can I fix my Scan function? Is it even possible to do this with a map type?