accessing.md

layout	title
article	Accessing the Database

Now that you've loaded the driver package, you're ready to create a database object, a sql.DB.

现在您已经加载了驱动程序包，您已准备好创建一个数据库对象sql.DB. 要创建sql.DB，请使用sql.Open（）。这将返回* sql.DB：

To create a sql.DB, you use sql.Open(). This returns a *sql.DB:

func main() {
	db, err := sql.Open("mysql",
		"user:password@tcp(127.0.0.1:3306)/hello")
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()
}

In the example shown, we're illustrating several things:

1. The first argument to sql.Open is the driver name. This is the string that the driver used to register itself with database/sql, and is conventionally the same as the package name to avoid confusion. For example, it's mysql for github.com/go-sql-driver/mysql. Some drivers do not follow the convention and use the database name, e.g. sqlite3 for github.com/mattn/go-sqlite3 and postgres for github.com/lib/pq.
   sql.Open的第一个参数是驱动程序名称。这是驱动程序用于向database / sql注册自身的字符串，并且通常与包名称相同以避免混淆。例如，它是github.com/go-sql-driver/mysql的mysql。某些驱动程序不遵循约定并使用数据库名称，例如sqlite3用于github.com/mattn/go-sqlite3和postgres用于github.com/lib/pq。
2. The second argument is a driver-specific syntax that tells the driver how to access the underlying datastore. In this example, we're connecting to the "hello" database inside a local MySQL server instance.
   第二个参数是特定于驱动程序的语法，它告诉驱动程序如何访问基础数据存储区。在此示例中，我们将连接到本地MySQL服务器实例中的“hello”数据库。
3. You should (almost) always check and handle errors returned from all database/sql operations. There are a few special cases that we'll discuss later where it doesn't make sense to do this.
   您应该（几乎）始终检查并处理从所有数据库/ SQL操作返回的错误。我们将在稍后讨论一些特殊情况，这样做是没有意义的。
4. It is idiomatic to defer db.Close() if the sql.DB should not have a lifetime beyond the scope of the function.
   如果sql.DB的生命周期不应超出函数范围，则推迟db.Close（）是惯用的。

Perhaps counter-intuitively, sql.Open() does not establish any connections to the database, nor does it validate driver connection parameters. Instead, it simply prepares the database abstraction for later use. The first actual connection to the underlying datastore will be established lazily, when it's needed for the first time. If you want to check right away that the database is available and accessible (for example, check that you can establish a network connection and log in), use db.Ping() to do that, and remember to check for errors:

也许与直觉相反，sql.Open（）不会与数据库建立任何连接，也不会验证驱动程序连接参数。相反，它只是准备数据库抽象以供以后使用。当第一次需要时，将懒洋洋地建立与基础数据存储区的第一个实际连接。如果要立即检查数据库是否可用且可访问（例如，检查是否可以建立网络连接并登录），请使用db.Ping（）执行此操作，并记住检查错误：

err = db.Ping()
if err != nil {
	// do something here
}

Although it's idiomatic to Close() the database when you're finished with it, the sql.DB object is designed to be long-lived. Don't Open() and Close() databases frequently. Instead, create one sql.DB object for each distinct datastore you need to access, and keep it until the program is done accessing that datastore. Pass it around as needed, or make it available somehow globally, but keep it open. And don't Open() and Close() from a short-lived function. Instead, pass the sql.DB into that short-lived function as an argument.

尽管在完成数据库时Close（）数据库是惯用的，但sql.DB对象的设计是长期存在的。不经常打开（）和关闭（）数据库。而是为您需要访问的每个不同数据存储创建一个sql.DB对象，并保留它直到程序完成访问该数据存储。根据需要传递它，或者以某种方式在全球范围内提供它，但保持打开状态。并且不要从短期函数中打开（）和关闭（）。相反，将sql.DB作为参数传递给该短期函数。

If you don't treat the sql.DB as a long-lived object, you could experience problems such as poor reuse and sharing of connections, running out of available network resources, or sporadic failures due to a lot of TCP connections remaining in TIME_WAIT status. Such problems are signs that you're not using database/sql as it was designed.

如果不将sql.DB视为长期存在的对象，则可能会遇到诸如重用和连接共享不良，可用网络资源不足或偶发故障等问题，因为TIME_WAIT中存在大量TCP连接状态。这些问题表明你没有像设计那样使用数据库/ sql。

Now it's time to use your sql.DB object.

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