使用C＃计算其中包含特定字符串变量的mysql数据库行的数量并将其显示为int时出错

Question

The code I am writing is to check how many employees are going to lunch at the same time. The information is in a MySQL table named: "edata" in the column named: "Lunchtime", and are stored as a string such as "4:00pm-5:00pm".

Name   |   Lunchtime
------------------------
Paul       4:00pm-5:00pm
Mike       4:00pm-5:00pm
Aaron      1:00pm-2:00pm

The ultimate goal is to count the number of shifts that are chosen by the "lunchTimes.Text" variable and display how many employees selected the shift as an int named: "count".

ie Program user selects the "4:00pm-5:00pm" option, and the program returns "2" since 2 employees have selected that time slot.

private void select_btn_Click(object sender, EventArgs e)
    {

        shiftLunch = lunchTimes.Text;

        string constring = "datasource=127.0.0.1;port=3306;username=root;password=password";
        string Query = "select count(Lunchtime) from database.edata where Lunchtime= '"+shiftLunch+"';";

        MySqlConnection conDataBase = new MySqlConnection(constring);
        MySqlCommand cmdDataBase = new MySqlCommand(Query, conDataBase);

        conDataBase.Open();
        Int32 count = (Int32)cmdDataBase.ExecuteScalar();


        Console.WriteLine(count);

Currently I am getting this error:

"An unhandled exception of type 'System.InvalidCastException' occurred in First_cSharp_App.exe Additional information: Specified cast is not valid."

At this line:

Int32 count = (Int32)cmdDataBase.ExecuteScalar();

I'm new to this so I apologize for any confusion.

Answer 1

This is because ExecuteScalar returns object which couldn't explicitly converted to Int32 at Runtime.

The proper way will be doing the following:

int count = (int)(cmdDataBase.ExecuteScalar());