GoLang PGX Postgresql

Question

I am looking to switch from lib/pg over to pgx but I cannot get a simple working select to work in pgx. Wondering if someone can point out what is wrong with this code. Why it is not working?

No problem with lib/pg but with pgx their must be something that is missing. I modified the test code from pgx example code to test out my select.

I have posted the code that I modified along with the error when code runs. I cannot see how I could have invalid memory address because the select returns. Maybe someone can point out what is going on with this code.

package main

import (
        "context"
        "fmt"
        "os"

        "github.com/jackc/pgx"
)

var conn *pgx.Conn
var err error

func main() {
        conn, err = pgx.Connect(context.Background(), os.Getenv("DATABASE_URL"))

        if err != nil {
                fmt.Fprintf(os.Stderr, "Unable to connection to database: %v\n", err)
                os.Exit(1)
        }
        listTasks()
        defer conn.Close(context.Background())
}

func listTasks() error {
        rows, _ := conn.Query(context.Background(), "select * from signal")

        for rows.Next() {
                var s string
                var id int32
                var v float64
                var description string
                var description2 string
                err := rows.Scan(&s, &id, &v, &description, &description2)
                if err != nil {
                        return err
                }
                fmt.Printf("%d. %s\n", id, description)
        }

        return rows.Err()
}

This is the error I get

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x4 pc=0x29eb30]

goroutine 1 [running]:
github.com/jackc/pgx.(*Conn).Query(0x0, 0x38deb8, 0x1414090, 0x3238d7, 0x14, 0x0, 0x0, 0x0, 0x14126c0, 0x192e8, ...)
        /home/forex/go/src/github.com/jackc/pgx/conn.go:585 +0x18
main.listTasks(0x38deb8, 0x1414090)
        /usr/local/forex/test-pgx.go:27 +0x58
main.main()
        /usr/local/forex/test-pgx.go:22 +0xbc

Answer 1

You are redefining conn below:

conn, err := pgx.Connect(context.Background(), os.Getenv("DATABASE_URL"))

So you're not assigning the global conn.

Change that to:

var err error
conn, err=px.Connect(...)

According to language spec:

Unlike regular variable declarations, a short variable declaration may redeclare variables provided they were originally declared earlier in the same block (or the parameter lists if the block is the function body) with the same type, and at least one of the non-blank variables is new.

conn is not defined in the same block, so the short declaration is defining conn and err, instead of assigning to conn.