Scan receives unexpected type []uint8 using mysql driver

[nkovacs]

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

It receives a []uint8 with the value [52 50] instead, which is actually the string "42".
If I use the standard library's Scan function, Foo.Scan receives an int64.

package main

import "fmt"
import _ "github.com/go-sql-driver/mysql"
import "github.com/jinzhu/gorm"

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
}

type FooModel struct {
        Foo Foo
}

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

        db.AutoMigrate(FooModel{})

        db.Create(&FooModel{Foo: Foo(42)})

        var fooModel FooModel
        db.Debug().First(&fooModel)
        fmt.Println(fooModel)

        stmtOut, err := db.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)
}

[jinzhu]

use parseTime=true when connect the database https://github.com/go-sql-driver/mysql#parsetime

[nkovacs]

This isn't a time value.

[nkovacs]

Turns out this is a bug in the mysql driver.

The difference is caused by me using a prepared statement, while gorm does not.
Gorm's code runs into mysqlConn.Query: https://github.com/go-sql-driver/mysql/blob/72ea5d0b32a04c67710bf63e97095d82aea5f352/connection.go#L305
That creates a textRows type, which returns strings for everything.
With the prepared statement, it executes mysqlStmt.Query: https://github.com/go-sql-driver/mysql/blob/b4db83c6faa0dc87d33f0bd7cdc81c7078594278/statement.go#L84
That creates a binaryRows type, which correctly returns an int.

So that's why I thought it was a bug in gorm, but I've tried it with db.DB().QueryRow now, it's incorrect.

Edit: bug report is here: go-sql-driver/mysql#441