How do I preprocess rows fetched with sqlx?

Question

Consider the following example:

package main

import (
    "fmt"
    "github.com/jmoiron/sqlx"
    _ "github.com/go-sql-driver/mysql"
)

type Data struct {
    Stuff string
}

func main() {
    db, _ := sqlx.Connect("mysql", "root:root@(localhost:3306)/data")
    var datas []Data
    db.Select(&datas, "select 'a,b' stuff from data limit 10")
    fmt.Println(datas)
}

What I'd like to do is have Stuff as []string, where it would be split by ,. I guess I could add an extra []string field and loop over the results populating this field and removing the source data, but that seems inefficient. What's the canonical way to do this in sqlx?

Answer 1

While this is not supported out of the box you can create custom struct implementing Scanner interface (https://golang.org/pkg/database/sql/#Scanner):

type StringList []string

// Scan implements Scanner interface and parses 
// database result to StringList struct.
func (s *StringList) Scan(src interface{}) error {
    var source string

    switch src.(type) {
    case string:
        source = src.(string)
    case []byte:
        source = string(src.([]byte))
    default:
        return errors.New("Incompatible type for StringList")
    }

    *s = strings.Split(source, ",")
    for i := range *s {
        (*s)[i] = strings.TrimSpace((*s)[i])
    }

    return nil
}

And use this struct instead of string:

type Data struct {
    Stuff StringList
}