大猩猩Mux和GORM失败

Question

I followed this tutorial on how to setup a basic API with PostgreSQL, Gorilla Mux and GORM.

This is my app:

package main

import (
    "encoding/json"
    "net/http"

    "github.com/gorilla/mux"
    "github.com/jinzhu/gorm"
    _ "github.com/jinzhu/gorm/dialects/postgres"
)

var db *gorm.DB


type Ticket struct {
    gorm.Model
    InfoHash string
    Status   *int `gorm:"default:'0'"`
}


func main() {
    router := mux.NewRouter()

    db, err := gorm.Open("postgres", "host=localhost user=user dbname=db_development password=password sslmode=disable")
    db.LogMode(true)

    if err != nil {
        panic(err)
    }
    defer db.Close()

    db.AutoMigrate(&Ticket{})

    router.HandleFunc("/", TicketsIndex).Methods("GET")

    http.ListenAndServe(":3000", router)
}

func TicketsIndex(w http.ResponseWriter, r *http.Request) {
    tickets := []Ticket{}
    db.Find(&tickets)
    json.NewEncoder(w).Encode(&tickets)
}

The problem is when I visit localhost:3000, the server just stops with no error logs, just stops and exit the app. It should return the tickets stored in the database as JSON.

I got it working if I open the database in my TicketsIndex function and close it, like this:

func TicketsIndex(w http.ResponseWriter, r *http.Request) {
  db, err := gorm.Open("postgres", "host=localhost user=user dbname=db_development password=password sslmode=disable")
  tickets := []Ticket{}
  db.Find(&tickets)
  json.NewEncoder(w).Encode(&tickets)
  defer db.Close()
}

But I think this is not the proper way. I also try to move this code into the main function and also works:

tickets := []Ticket{}
db.Find(&tickets)

So I am assuming it could be the global variable var db *gormDB that is not being assigned correctly. What am I doing wrong?

Answer 1

When you type db, err := ... you're actually shadowing the global var db with a function-local variable named db, not assigning to the global one. You need to use the equal sign (= vs :=) to assign to an already defined var. That also means you'll need to write var err error inside of main scope before the assignment, since you're no longer getting declaration automatically from :=.