C# db 示例代码抛出“连接属性尚未初始化”答案

【问题标题】：C# db sample code throws "Connection property has not been initialized"C# db 示例代码抛出“连接属性尚未初始化”
【发布时间】：2019-07-12 10:14:15
【问题描述】：

我已经在我的机器上安装了sql server db，Visual Studio“服务器资源管理器”可以连接到它，并且连接字符串在“属性”中提供，然后我使用这个字符串编写我的C#代码如下：

SqlConnection conn = new SqlConnection(
    "Data Source=MININT-EP12N1V;Initial Catalog=EmployeeDB;Integrated Security=True");
conn.Open();
SqlCommand cmd = new SqlCommand("select FirstName, LastName from Employees");
//above sql can be executed in sql server management studio successfully.
SqlDataReader reader = cmd.ExecuteReader();//throws exception
while (reader.Read())
{
    Console.Write("{1}, {0}", reader.GetString(0), reader.GetString(1));
}
reader.Close();
cmd.Dispose();
conn.Close();

抛出异常：

Unhandled Exception: System.InvalidOperationException: ExecuteReader: Connection property has not been initialized.
   at System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, TaskCompletionSource`1 completion, Int32 timeout, Task& task, Boolean& usedCache, Boolean asyncWrite, Boolean inRetry)
   at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method)
   at System.Data.SqlClient.SqlCommand.ExecuteReader(CommandBehavior behavior, String method)

那么如何解决呢？

【问题讨论】：

通过设置SqlCommand的Connection属性？

标签： c# sql-server exception connection

【解决方案1】：

您没有将SqlConnection 传递给SqlCommand，这是必需的，因为除非您提供连接详细信息，否则命令不知道它需要在哪个服务器上执行查询。

试试：

SqlCommand cmd = new SqlCommand("select FirstName, LastName from Employees",conn);

您总是可以看到examples provided in the docs。

您可以在文档示例中看到要执行的方法。您应该在使用中包装连接，以便在代码块退出时立即将其处理掉：

using(SqlConnection conn = new SqlConnection(
    "Data Source=MININT-EP12N1V;Initial Catalog=EmployeeDB;Integrated Security=True"))
{

    SqlCommand cmd = new SqlCommand("select FirstName, LastName from Employees");
    SqlDataReader reader = cmd.ExecuteReader();
    conn.Open();
    while (reader.Read())
    {
        Console.Write("{1}, {0}", reader.GetString(0), reader.GetString(1));
    }
    reader.Close();
    cmd.Dispose();
}

【讨论】：