代码中使用连接是什么

发布于 2024-09-30 13:44:46 字数 729 浏览 7 评论 0原文

代码中 using (connection) 的目的是什么 - 请解释一下

static void HasRows(SqlConnection connection)
{
    using (connection)/// what is this line 
    {
        SqlCommand command = new SqlCommand(
          "SELECT CategoryID, CategoryName FROM Categories;",
          connection);
        connection.Open();

        SqlDataReader reader = command.ExecuteReader();

        if (reader.HasRows)
        {
            while (reader.Read())
            {
                Console.WriteLine("{0}\t{1}", reader.GetInt32(0),
                    reader.GetString(1));
            }
        }
        else
        {
            Console.WriteLine("No rows found.");
        }
        reader.Close();
    }
}

原文

What is the purpose of using (connection) in the code - please explain me

static void HasRows(SqlConnection connection)
{
    using (connection)/// what is this line 
    {
        SqlCommand command = new SqlCommand(
          "SELECT CategoryID, CategoryName FROM Categories;",
          connection);
        connection.Open();

        SqlDataReader reader = command.ExecuteReader();

        if (reader.HasRows)
        {
            while (reader.Read())
            {
                Console.WriteLine("{0}\t{1}", reader.GetInt32(0),
                    reader.GetString(1));
            }
        }
        else
        {
            Console.WriteLine("No rows found.");
        }
        reader.Close();
    }
}

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雪花飘飘的天空 2024-10-07 13:44:46

using (connection){
    connection.Open();
}

确保应用程序使用完连接后关闭连接。
类似于 Try Catch。

try{
    connection.Open();
}
catch{
}
finally{
    connection.Dispose(); 
}

释放连接是关闭连接的另一种说法。打开的连接可能会泄漏内存，如果内存太多，它可能会减慢或冻结您所连接的任何内容。

即使您从所在类返回某些内容，using 函数也会关闭连接。与 try catch 相同。无论括号内发生什么，它总是关闭连接。即使存在超出类/应用程序的异常，连接仍然会关闭

using (connection){
    connection.Open();
}

makes sure that connection is closed when the application is done using it.
similar to a Try Catch.

try{
    connection.Open();
}
catch{
}
finally{
    connection.Dispose(); 
}

Disposing of the connection is another way of saying closing a connection. An open connection can leak memory and if you have too many it can slow down or freeze up whatever you are connecting to.

the using function closes the connection even after you return something from the class you are in. same as the try catch. it always closes the connection no matter what happens inside the brackets. even if there is an exception that breaks out of the class/application the connection still gets closed

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最终幸福 2024-10-07 13:44:46

使用

引用自网站：

using 语句允许程序员指定使用资源的对象何时应该释放它们。提供给 using 语句的对象必须实现 IDisposable 接口。该接口提供了Dispose方法，该方法应该释放对象的资源。

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猫七 2024-10-07 13:44:46

我可能会将该方法重写为如下所示：

static void HasRows(string connectionString)
{
    using (var connection = new SqlConnection(connectionString))
    using(var command = new SqlCommand("SELECT CategoryID, CategoryName FROM Categories;",
        connection))
    {
        connection.Open();

        using (var reader = command.ExecuteReader())
        {
            if (reader.HasRows)
            {
                while (reader.Read())
                {
                    Console.WriteLine("{0}\t{1}", reader.GetInt32(0),
                        reader.GetString(1));
                }
            }
            else
            {
                Console.WriteLine("No rows found.");
            }
        }
    }
}

在原始实现中，调用者可能位于 ObjectDisposeException 异常的接收端，因为 SqlConnection 是作为参数传入的。

I would probably re-write the method to something like the following:

static void HasRows(string connectionString)
{
    using (var connection = new SqlConnection(connectionString))
    using(var command = new SqlCommand("SELECT CategoryID, CategoryName FROM Categories;",
        connection))
    {
        connection.Open();

        using (var reader = command.ExecuteReader())
        {
            if (reader.HasRows)
            {
                while (reader.Read())
                {
                    Console.WriteLine("{0}\t{1}", reader.GetInt32(0),
                        reader.GetString(1));
                }
            }
            else
            {
                Console.WriteLine("No rows found.");
            }
        }
    }
}

In your original implementation the caller could be at the receiving end of an ObjectDisposedException exception, because the SqlConnection is passed in as a parameter.

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