连接必须有效并在数据库中插入记录时打开

Question

我试图将客户端详细信息插入数据库，但获得此异常

连接必须有效且开放。 at MySql.Data.MySqlClient.MySqlCommand.Throw（Exception ex）at MySql.Data.MySqlClient.MySqlCommand.CheckState（）at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader（CommandBehavior behavior）at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader （）at book_online.saveClient_Click的MySql.Data.MySqlClient.MySqlCommand.ExecuteNonQuery（）（Object sender，EventArgs e）

MySqlConnection con = new MySqlConnection();
con.ConnectionString = ConfigurationManager.ConnectionStrings("conio").ConnectionString();
MySqlCommand cmd = new MySqlCommand();
cmd.CommandText = "INSERT INTO clientsDetails (clientName, companyAddress, city, contactPersonName, contactNumber1) Values(@clientName, @companyAddress, @city, @contactPersonName, @contactNumber1)";
cmd.Parameters.AddWithValue("@clientName", companyName.Text);
cmd.Parameters.AddWithValue("@companyAddress", companyAddress.Text);
cmd.Parameters.AddWithValue("@city", companyCity.Text);
cmd.Parameters.AddWithValue("@contactPersonName", concernPersonName.Text);
cmd.Parameters.AddWithValue("@contactNumber1", countryCodeWithNumber);
con.Open();
cmd.ExecuteNonQuery();
con.Close();

Answer 1

那么你已经打开了连接并执行了命令，但是你忘了为命令分配连接 ，那么只有代码可以正常工作。 强烈建议您也使用。 然后代码将如下所示：

using (MySqlConnection con = new MySqlConnection())
{
    con.ConnectionString = ConfigurationManager.ConnectionStrings("conio").ConnectionString();
    string queryText = "INSERT INTO clientsDetails (clientName, companyAddress, city, contactPersonName, contactNumber1) Values(@clientName, @companyAddress, @city, @contactPersonName, @contactNumber1)";
    using (MySqlCommand cmd = new MySqlCommand(queryText, con))
    {
        cmd.Parameters.AddWithValue("@clientName", companyName.Text);
        cmd.Parameters.AddWithValue("@companyAddress", companyAddress.Text);
        cmd.Parameters.AddWithValue("@city", companyCity.Text);
        cmd.Parameters.AddWithValue("@contactPersonName", concernPersonName.Text);
        cmd.Parameters.AddWithValue("@contactNumber1", countryCodeWithNumber);
        con.Open();
        cmd.ExecuteNonQuery();
    }
}

Answer 2

命令缺少连接字符串。

MySqlConnection con = new MySqlConnection();
con.ConnectionString = ConfigurationManager.ConnectionStrings("conio").ConnectionString();
MySqlCommand cmd = new MySqlCommand();
cmd.Connection = con;
cmd.CommandText = "INSERT INTO clientsDetails (clientName, companyAddress, city, contactPersonName, contactNumber1) Values(@clientName, @companyAddress, @city, @contactPersonName, @contactNumber1)";
cmd.Parameters.AddWithValue("@clientName", companyName.Text);
cmd.Parameters.AddWithValue("@companyAddress", companyAddress.Text);
cmd.Parameters.AddWithValue("@city", companyCity.Text);
cmd.Parameters.AddWithValue("@contactPersonName", concernPersonName.Text);
cmd.Parameters.AddWithValue("@contactNumber1", countryCodeWithNumber);
con.Open();
cmd.ExecuteNonQuery();
con.Close();

Answer 3

您没有为命令指定连接对象：

cmd.Connection = con;

此外，最好使用一个using块，当它退出该块时会自动关闭你的连接：

using(MySqlConnection con = new MySqlConnection())
{
   con.ConnectionString =
                       ConfigurationManager.ConnectionStrings("conio").ConnectionString();

   MySqlCommand cmd = new MySqlCommand();
   cmd.CommandText = @"INSERT INTO clientsDetails
              (clientName, companyAddress, city, contactPersonName, contactNumber1)
               Values
              (@clientName, @companyAddress, @city, @contactPersonName, @contactNumber1)";

   cmd.Connection = con;
   cmd.Parameters.AddWithValue("@clientName", companyName.Text);
   cmd.Parameters.AddWithValue("@companyAddress", companyAddress.Text);
   cmd.Parameters.AddWithValue("@city", companyCity.Text);
   cmd.Parameters.AddWithValue("@contactPersonName", concernPersonName.Text);
   cmd.Parameters.AddWithValue("@contactNumber1", countryCodeWithNumber);
   con.Open();
   cmd.ExecuteNonQuery();
}

只是为了信息的using关键字可以编译生成一个try...finally的封闭块，并调用Dispose内部的物体上using （ con在你的情况下）产生finally块内。 因此，保证在最终得到保证的所有情况下都能关闭您的连接）