Scan receives unexpected type []uint8 when using db.QueryRow

[nkovacs]

Issue description

I've created a custom type that implements sql.Scanner.

The documentation of this interface claims that Scan will receive one of the following types:

• int64
• float64
• bool
• []byte
• string
• time.Time
• nil - for NULL values

If I use a prepared statement, it receives an int64, which is correct. If I just use db.QueryRow, it receives a []uint8 with the value [52 50] instead, which is actually the string "42". It should receive int64 in both cases.

Example code

-- phpMyAdmin SQL Dump
-- version 4.4.13.1deb1
-- http://www.phpmyadmin.net
--
-- Host: localhost
-- Generation Time: Mar 28, 2016 at 12:24 PM
-- Server version: 5.6.28-0ubuntu0.15.10.1
-- PHP Version: 5.6.11-1ubuntu3.1

SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
SET time_zone = "+00:00";


/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8mb4 */;

--
-- Database: `testdb`
--

-- --------------------------------------------------------

--
-- Table structure for table `foo_models`
--

CREATE TABLE IF NOT EXISTS `foo_models` (
  `foo` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

--
-- Dumping data for table `foo_models`
--

INSERT INTO `foo_models` (`foo`) VALUES
(42);

/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;

package main

import (
    "database/sql"
    "fmt"

    _ "github.com/go-sql-driver/mysql"
)

type Foo int

// Scan implements the database/sql.Scanner interface
func (f *Foo) Scan(value interface{}) error {
    switch value := value.(type) {
    case int64:
        *f = Foo(value)
    default:
        return fmt.Errorf("Invalid database type: %T %v", value, value)
    }
    return nil
}

func main() {
    db, err := sql.Open("mysql", "user:pass@/testdb?parseTime=true")
    if err != nil {
        panic(err)
    }

    stmtOut, err := db.Prepare("SELECT foo FROM foo_models LIMIT 1")
    if err != nil {
        panic(err)
    }
    defer stmtOut.Close()

    var foo Foo
    err = stmtOut.QueryRow().Scan(&foo)
    if err != nil {
        panic(err)
    }

    fmt.Println(foo)

    row := db.QueryRow("SELECT foo FROM foo_models LIMIT 1")
    err = row.Scan(&foo)
    if err != nil {
        panic(err)
    }

    fmt.Println(foo)
}

Configuration

Driver version (or git SHA): 66312f7

Go version: go1.6 linux/amd64

Server version: 5.6.28-0ubuntu0.15.10.1

Server OS: Ubuntu 15.10

[julienschmidt]

See #407 / #366 / #86.

If the driver would know what type the user passed to .Scan(..) we would certainly do this. But the database/sql interface hides that information from the driver.

[nkovacs]

Yeah, I looked at those issues, your reply was to not scan into interface{}, but I'm not doing that.
Though that probably doesn't make much of a difference, since the conversion is also handled by the sql package.

[YasiruR]

Any update on this?

[99848873]

Is this issue resloved?

[shogo82148]

it's a specification of the driver.
see #441 (comment)
this issue will be never updated.