Question

我有8个选项卡，每个选项卡包含每个选项卡中的记录数量，以及一个应该计算每个选项卡中记录数量的函数，并将其放在选项卡的标题名称中，如下所示：

public void count_records(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Test"].ConnectionString);
        string[] commands = {
                                "SELECT * FROM myTable",
                                "SELECT * FROM myTable WHERE Status=2",
                                "SELECT * FROM myTable WHERE Status=3",
                                "SELECT * FROM myTable WHERE Status=8",
                                "SELECT * FROM myTable WHERE Status=4",
                                "SELECT * FROM myTable WHERE Status=7",
                                "SELECT * FROM myTable WHERE Status=1",
                                "SELECT * FROM myTable WHERE Status=5"
                            };
        int[] LLCount = new int[commands.Length];
        try
        {
            for (int i = 0; i < commands.Length; i++)
            {
                SqlCommand cmd = new SqlCommand(commands[i], con);
                SqlDataReader reader;
                int count = 0;
                con.Open();
                reader = cmd.ExecuteReader();
                while (reader.Read())
                {
                    count++;
                }
                LLCount[i] = count;
                myTab1.HeaderText += " (" + LLCount[0] + ")";
                myTab2.HeaderText += " (" + LLCount[1] + ")";
                myTab3.HeaderText += " (" + LLCount[2] + ")";
                myTab4.HeaderText += " (" + LLCount[3] + ")";
                myTab5.HeaderText += " (" + LLCount[4] + ")";
                myTab6.HeaderText += " (" + LLCount[5] + ")";
                myTab7.HeaderText += " (" + LLCount[6] + ")";
                myTab8.HeaderText += " (" + LLCount[7] + ")";
            }
        }
        catch (Exception ex) { string ee = ex.Message; }
        finally { con.Close(); }
    }

现在，我面临的问题是读者正确获取第一个命令字符串的记录数 “LLCount [0]” 但其余部分它们是零。

修改

我添加了reader.Close（）;并将分配移到了循环之外但是它甚至没有像以前那样显示零或任何东西。所以，我认为不管你是否放了reader.Close（）;或不。

Answer 1

在代码中查找// * 以查找差异。主要内容是我将con.Open();放在for loop之前。再次打开相同的连接会在未关闭连接时抛出错误。此错误在catch块中被捕获，

public void count_records(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["Test"].ConnectionString);
    //*** See Count(*) in the sql
    string[] commands = {
                       "SELECT count(*) FROM myTable",
                        "SELECT count(*) FROM myTable WHERE Status=2",
                        "SELECT count(*) FROM myTable WHERE Status=3",
                        "SELECT count(*) FROM myTable WHERE Status=8",
                        "SELECT count(*) FROM myTable WHERE Status=4",
                        "SELECT count(*) FROM myTable WHERE Status=7",
                        "SELECT count(*) FROM myTable WHERE Status=1",
                        "SELECT count(*) FROM myTable WHERE Status=5"

                    };
    int[] LLCount = new int[commands.Length];
    try
    {
        //*****This is the change I made
        con.Open();

        for (int i = 0; i < commands.Length; i++)
        {
            SqlCommand cmd = new SqlCommand(commands[i], con);

            int count = 0;
            //*** Se the use of ExecuteScalar
            count =Convert.ToInt32(  cmd.ExecuteScalar());
            LLCount[i] = count;
        }

        //***Now Assign the Tab Headers

    }
    catch (Exception ex) { string ee = ex.Message; }
    finally { con.Close(); }
}

}

记录来自数据库

1 个答案: