Scan unstructured JSON BYTEA into map[string]string - sql

Question

This seems like a common problem and may be posted somewhere already, but I can't find any threads talking about it, so here is the problem:
I have a Postgres table storeing a column of type BYTEA.
CREATE TABLE foo (
id VARCHAR PRIMARY KEY,
json_data BYTEA
)
The column json_data is really just JSON stored as BYTEA (It's not ideal I know). It is unstructured, but guaranteed to be of string -> string JSON.
When I query this table, I need to scan the query SELECT * FROM foo WHERE id = $1 into the following struct:
type JSONData map[string]string
type Foo struct {
ID string `db:"id"`
Data JSONData `db:"json_data"`
}
I'm using sqlx's Get method. When I execute a query I'm getting the error message sql: Scan error on column index 1, name "json_data": unsupported Scan, storing driver.Value type []uint8 into type *foo.JSONData.
Obviously, the scanner is having trouble scanning the JSON BYTEA into a map. I can implement my own scanner and call my custom scanner on the json_data column, but I'm wondering if there are better ways to do this. Could my JSONData type implement an existing interface to do this automatically?

Answer 1

As suggested by #iLoveReflection, implementing the Scanner interface on *JSONData worked. Here is the actual implementation:
func (j *JSONData) Scan(src interface{}) error {
b, ok := src.([]byte)
if !ok {
return errors.New("invalid data type")
}
return json.Unmarshal(b, j)
}