GoLang Dynamic SQL Query in App Engine - mysql

Question

I want to make dynamic sql in GoLang and I cant seem to find the correct way to do it.
Basically, I just want to do:
query := "SELECT id, email, something FROM User"
var paramValues []string
filterString := ""
if userParams.Name != "" {
paramString += " WHERE id = ?"
paramValues = append(paramValues, userParams.Name)
}
if userParams.UserID != "" {
if len(paramString) > 0 {
paramString += " AND"
} else {
paramString += " WHERE"
}
paramString += " email = ?"
paramValues = append(paramValues, userParams.UserID)
}
stmtOut, err := db.Prepare(query + paramString)
err = stmtOut.QueryRow(paramValues).Scan(&id, &email, &something)
Related to building a dynamic query in mysql and golang
I've been unable to find a solid way to do this that doesn't allow sql injection. The issue with my above solution is that QueryRow() does not take a []string as a parameter.
I want to protect from SQL Injection, so fmt.Sprintf doesn't really solve the problem.
This way I can allow searches on user using either the ID or Email, and I will also use this logic for different objects with more searchable fields.
I'm using go-sql-driver/mysql

Answer 1

Here's something which I can run on my local machine (go1.8 linux/amd64 and current GO MySQL driver 1.3).
Couple of ways are demonstrated.
package main
import (
"database/sql"
"log"
_ "github.com/go-sql-driver/mysql"
"fmt"
)
// var db *sql.DB
// var err error
/*
Database Name/Schema : Test123
Table Name: test
Table Columns and types:
number INT (PRIMARY KEY)
cube INT
*/
func main() {
//Username root, password root
db, err := sql.Open("mysql", "root:root#tcp(127.0.0.1:3306)/Test123?charset=utf8")
if err != nil {
fmt.Println(err) // needs proper handling as per app requirement
return
}
defer db.Close()
err = db.Ping()
if err != nil {
fmt.Println(err) // needs proper handling as per app requirement
return
}
//Prepared statement for inserting data
stmtIns, err := db.Prepare("INSERT INTO test VALUES( ?, ? )") // ? = placeholders
if err != nil {
panic(err.Error()) // needs proper handling as per app requirement
}
defer stmtIns.Close()
//Insert cubes of 1- 10 numbers
for i := 1; i < 10; i++ {
_, err = stmtIns.Exec(i, (i * i * i)) // Insert tuples (i, i^3)
if err != nil {
panic(err.Error()) // proper error handling instead of panic in your app
}
}
num := 3
// Select statement
dataEntity := "cube"
condition := "WHERE number=? AND cube > ?"
finalStatement := "SELECT " + dataEntity + " FROM test " + condition
cubeLowerLimit := 10
var myCube int
err = db.QueryRow(finalStatement, num, cubeLowerLimit).Scan(&myCube)
switch {
case err == sql.ErrNoRows:
log.Printf("No row with this number %d", num)
case err != nil:
log.Fatal(err)
default:
fmt.Printf("Cube for %d is %d\n", num, myCube)
}
var cubenum int
// //Prepared statement for reading data
stmtRead, err := db.Prepare(finalStatement)
if err != nil {
panic(err.Error()) // needs proper err handling
}
defer stmtRead.Close()
// Query for cube of 5
num = 5
err = stmtRead.QueryRow(num, cubeLowerLimit).Scan(&cubenum)
switch {
case err == sql.ErrNoRows:
log.Printf("No row with this number %d", num)
case err != nil:
log.Fatal(err)
default:
fmt.Printf("Cube number for %d is %d\n", num, cubenum)
}
}
If you run it subsequent times, you need to delete the rows in the database so that the inserts won't create a panic (or alternatively change the insert rows code so that it doesn't panic). I haven't tried it on Google App Engine. Hope this helps.