Go SQL driver get interface{} column values - mysql

Question

I am trying to use go sql driver to read from database tables and I am converting the values to []map[string]interface{}. The column name is the key of the map and the values are of interface{}. I am adding all the columns into an array. I am using the code sample for "RawBytes" at https://github.com/go-sql-driver/mysql/wiki/Examples as an example to start with.
However, in the example -all the column values are converted to string as follows,
// Fetch rows
for rows.Next() {
// get RawBytes from data
err = rows.Scan(scanArgs...)
if err != nil {
panic(err.Error()) // proper error handling instead of panic in your app
}
// Now do something with the data.
// Here we just print each column as a string.
var value string
for i, col := range values {
// Here we can check if the value is nil (NULL value)
if col == nil {
value = "NULL"
} else {
value = string(col) //ATTN : converted to string here
}
fmt.Println(columns[i], ": ", value)
}
fmt.Println("-----------------------------------")
}
Is there a way to retain it as interface{} so I can do the necessary type casting while using the columns from []map[string]interface{}

Answer 1

See this https://stackoverflow.com/questions/20271123/go-lang-sql-in-parameters answer which my answer is based on. Using that you can do something like this:
var myMap = make(map[string]interface{})
rows, err := db.Query("SELECT * FROM myTable")
defer rows.Close()
if err != nil {
log.Fatal(err)
}
colNames, err := rows.Columns()
if err != nil {
log.Fatal(err)
}
cols := make([]interface{}, len(colNames))
colPtrs := make([]interface{}, len(colNames))
for i := 0; i < len(colNames); i++ {
colPtrs[i] = &cols[i]
}
for rows.Next() {
err = rows.Scan(colPtrs...)
if err != nil {
log.Fatal(err)
}
for i, col := range cols {
myMap[colNames[i]] = col
}
// Do something with the map
for key, val := range myMap {
fmt.Println("Key:", key, "Value Type:", reflect.TypeOf(val))
}
}
Using the reflect package you can then get the Type for each column as needed as demonstrated with the loop at the end.
This is generic and will work with any table, number of columns etc.

Answer 2

AFter a long struggle i found out the solution. Check belowfunction that converts sql.RawBytes to Int64. This can be easily altered to fit any data type
func GetInt64ColumnValue(payload sql.RawBytes) (int64, error) {
content := reflect.ValueOf(payload).Interface().(sql.RawBytes) // convert to bytes
data := string(content) //convert to string
i, err := strconv.ParseInt(data,10,64) // convert to int or your preferred data type
if err != nil {
log.Printf("got error converting %s to int error %s ",data,err.Error())
return 0, err
}
return i, nil
}