sql connection shared between different package files

[eauction...@hotmail.com]

I have tried for days to get my head round this, all i want to do is open a mysql database once, with a global db variable and then in different package files within the app use that same db variable to access the files,

here is what I have so far

C:\go\src\testsql\dbpackage\dbpackage.go

import (

    "database/sql"

    "fmt"

)

var Db *sql.DB

func init() {

    Db, err := sql.Open("mysql",

        "remoteusername:remotepassord@tcp(remoteipaddress:3306)/remotedatabasename")

    if err != nil {

        fmt.Printf("openind db: error: %s\n", err)

    }

    err = Db.Ping()

    if err != nil {

        // do something here, we cant ping the database connection we just made.

        fmt.Printf("pinging db: error: %s\n", err)

    }

}

as I understand it the Db should be globally accessible, having a capital first letter? Correct or not?

Then I also have

c:\go\src\testsql\main.go

package main


import (
    "fmt"
    "testsql/dbpackage"
)


func main() {

    var (
        id    int
        title string
    )
    rows, err := dbpackage.Db.Query("select id, title from pages where id < ?", 100)


    if err != nil {
        fmt.Printf("select statement: error: %s\n", err)
    }
    defer rows.Close()
    for rows.Next() {
        err := rows.Scan(&id, &title)
        if err != nil {
            fmt.Printf("read row: error: %s\n", err)
        }
        fmt.Printf("%d %s\n", id, title)
    }
    err = rows.Err()
    if err != nil {
        fmt.Printf("final: error: %s\n", err)
    }
}


However, running this crashes out with 

C:/Go/bin/go.exe build -i [C:/Go/src/testsql]

Success: process exited with code 0.

C:/Go/src/testsql/testsql.exe [C:/Go/src/testsql]

openind db: error: sql: unknown driver "mysql" (forgotten import?)

panic: runtime error: invalid memory address or nil pointer dereference

[signal 0xc0000005 code=0x1 addr=0x0 pc=0x48a2f5]

goroutine 1 [running]:

database/sql.(*DB).conn(0x0, 0x43, 0x0, 0x0)

c:/go/src/database/sql/sql.go:634 +0x7b5

database/sql.(*DB).Ping(0x0, 0x0, 0x0)

c:/go/src/database/sql/sql.go:462 +0x41

testsql/dbpackage.init·1()

C:/Go/src/testsql/dbpackage/dbpackage.go:17 +0x14d

testsql/dbpackage.init()

C:/Go/src/testsql/dbpackage/dbpackage.go:23 +0x53

main.init()

C:/Go/src/testsql/main.go:31 +0x49

goroutine 2 [runnable]:

runtime.forcegchelper()

c:/go/src/runtime/proc.go:90

runtime.goexit()

c:/go/src/runtime/asm_amd64.s:2232 +0x1

goroutine 3 [runnable]:

runtime.bgsweep()

c:/go/src/runtime/mgc0.go:82

runtime.goexit()

c:/go/src/runtime/asm_amd64.s:2232 +0x1

goroutine 4 [runnable]:

runtime.runfinq()

c:/go/src/runtime/malloc.go:712

runtime.goexit()

c:/go/src/runtime/asm_amd64.s:2232 +0x1

Error: process exited with code 2.

Can anyone help me grasp what I am missing with this, I feel like I am missing something pretty fundemental...

[silviun...@gmail.com]

you appear to have forgotten the reference to the mysql driver in the dbpackage file

Import one of the mysql drivers  (first, do: go get github.com/go-sql-driver/mysql )

Then, add a line in your imports section in dbpackage.go

import (

    "database/sql"

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

    "fmt"

)

[eauction...@hotmail.com]

many thanks, I had forgot about that when I stripped the code out to make the example one for testing.
I have put the line into dbpackage.go, and imported the driver but it still crashes out with the following message

C:/Go/bin/go.exe build -i [C:/Go/src/testsql]

Success: process exited with code 0.

C:/Go/src/testsql/testsql.exe [C:/Go/src/testsql]

panic: runtime error: invalid memory address or nil pointer dereference

[signal 0xc0000005 code=0x1 addr=0x0 pc=0x4938e5]

goroutine 1 [running]:

database/sql.(*DB).conn(0x0, 0x0, 0x0, 0x0)

c:/go/src/database/sql/sql.go:634 +0x7b5

database/sql.(*DB).query(0x0, 0x6aa150, 0x28, 0xc082063f48, 0x1, 0x1, 0x40b003, 0x0, 0x0)

c:/go/src/database/sql/sql.go:933 +0x4a

database/sql.(*DB).Query(0x0, 0x6aa150, 0x28, 0xc082063f48, 0x1, 0x1, 0x0, 0x0, 0x0)

c:/go/src/database/sql/sql.go:924 +0xad

main.main()

C:/Go/src/testsql/main.go:14 +0x151

goroutine 5 [chan receive]:

database/sql.(*DB).connectionOpener(0xc08202ebe0)

c:/go/src/database/sql/sql.go:589 +0x53

created by database/sql.Open

c:/go/src/database/sql/sql.go:452 +0x323

Error: process exited with code 2.

[Ingo Oeser]

It'a scoping problem.
the Db variable in your init function is shadowing the global Db variable.

Try this
func init() {
var err error
Db , err = db.Open(.....)
// note the equals instead of colon equals above!
//....
}

[eauction...@hotmail.com]

THANK YOU

works a treat now, so it was because i was trying to create a new variable with := rather than just assigning it to the existing global!

for future reference for anyone with same problem, the updated func which works is as follows

func init() {

    var err error

    Db, err = sql.Open("mysql",

        "remoteuser:remotepassword@tcp(ipaddress:3306)/databasename")

    // note the equals instead of colon equals above!

    if err != nil {

        fmt.Printf("openind db: error: %s\n", err)

    }

    err = Db.Ping()

    if err != nil {

        // do something here, we cant ping the database connection we just made.

        fmt.Printf("pinging db: error: %s\n", err)

    }

}

thanks again, now I can crack on and start some serious learning :)

On Monday, 16 March 2015 20:54:09 UTC, eauction...@hotmail.com wrote: