GoLang Dynamic SQL Query in App Engine

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

Ravi R · Accepted Answer · 2017-09-14 09:15:08Z

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.

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