sqlmock custom converter

If you have been using sqlmock to mock database queries then, you might have or will encounter errors such as sql error unsupported []string, a slice of string if one of the args in the query is a byte slice.

This is cause the go std/sql driver doesn’t understand or support types other than the std ones.
Below are the types supported by the driver.Value interface.

// Value is a value that drivers must be able to handle.
// It is either nil, a type handled by a database driver's [NamedValueChecker]
// interface, or an instance of one of these types:

int64
float64
bool
[]byte
string
time.Time

So for user or driver defined types such as sql.NullString, pq.StringArray, we need to implement the ValueConverter interface. Source here.

The workaround for the above issue is to pass our own Custom Converter to the sqlmock which handles all the data types.
More discussion here.

converter.go

type CustomConverter struct{}
 
func (s CustomConverter) ConvertValue(v interface{}) (driver.Value, error) {
	switch v.(type) {
	case string:
		return v.(string), nil
	case []string:
		return v.([]string), nil
	case int:
		return v.(int), nil
	case bool:
		return v.(bool), nil
	case uint64:
		return v.(uint64), nil
	case pq.StringArray:
		var result []string
		for _, val := range v.(pq.StringArray) {
			result = append(result, val)
		}
		return result, nil
	case MessageAuthor:
		return string(v.(MessageAuthor)), nil
	case sql.NullString:
		if v.(sql.NullString).Valid {
			return v.(sql.NullString).String, nil
		}
		return nil, nil
	case MessageStatus:
		return string(v.(MessageStatus)), nil
	default:
		return nil, fmt.Errorf("cannot convert %T with value %v", v, v)
	}
}
 
// init
func GetMockDB() (*sql.DB, sqlmock.Sqlmock, error) {
	return sqlmock.New(sqlmock.ValueConverterOption(CustomConverter{}))
}
 

This will hopefully pass all your test cases and you sleep soundly.