Does db.Close() need to be called?

问题

So far the hardest part of Go has been understanding how to organize code. It seems incredibly simple on it's face but every time I've tried to do anything I run into circular imports or things like "exported func Start returns unexported type models.dbStore, which can be annoying to use".

Using the following code how do I call db.Close() or am I really not understanding how I'm supposed to provide the database to my models. Here's what I've got:

App.go

package app

import (
    "database/sql"

    // Comment
    _ "github.com/mattn/go-sqlite3"
)

var (
    // DB The database connection
    db *sql.DB
)

// Setup Sets up the many many app settings
func Setup() {
    d, err := sql.Open("sqlite3", "./foo.db")
    if err != nil {
        panic(err)
    }

    // TODO: How does the DB get closed?
    // defer db.Close()
    db = d
}

// GetDB Returns a reference to the database
func GetDB() *sql.DB {
    return db
}

Users.go

package models

import (
    "github.com/proj/org/app"
)

// User struct
type User struct {
    ID int
}

// CreateUser Creates a user
func (u *User) CreateUser() (int64, error) {

    // For the sake of brevity just make sure you can
    // "connect" to the database
    if err := app.GetDB().Ping(); err != nil {
        panic(err)
    }

    return 1234, nil
}

main.go

package main

import (
    "fmt"
    "net/http"

    _ "github.com/mattn/go-sqlite3"
    "github.com/proj/org/app"
    "github.com/proj/org/models"
)

func homeHandler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "You are home")
}

func subscribeHandler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "Subscribing...")
    u := models.User{}

    u.CreateUser()

}

func main() {
    fmt.Println("Running")

    app.Setup()

    http.HandleFunc("/", homeHandler)
    http.HandleFunc("/subscribe", subscribeHandler)

    err := http.ListenAndServe(":9090", nil)
    if err != nil {
        panic(err)
    }
}

I thought about doing a app.Shutdown() but that wouldn't work for my most normal use case which is CTRL-C. It would seem if I don't close the database the DB connections would just grow... Just trying to understand.

回答1:

It's not necessary to close the DB.

The returned DB is safe for concurrent use by multiple goroutines and maintains its own pool of idle connections. Thus, the Open function should be called just once. It is rarely necessary to close a DB.

From: https://golang.org/pkg/database/sql/#Open

When your program exits then any open connection is closed, it does not stay open somewhere in the ether awaiting your program to start again, so do not worry about the connections "growing" when you CTRL-C your app.

If, however, you still want to close it, then you can just export a CloseDB function the same way you do with GetDB.

App.go

// ...

func CloseDB() error {
    return db.Close()
}

main.go

// ...

func main() {
    // ...

    app.Setup()
    defer app.CloseDB()

    // ...

}

来源：https://stackoverflow.com/questions/50787804/does-db-close-need-to-be-called

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