运行查询时，Windows 窗体程序突然关闭。 如何在错误停止/崩溃之前捕获错误？

Question

I have a 3 PC setup that runs the POS-like program I created. 1 PC that acts as the server and the 2 as the client. I have a heavy query in the client-side that when executed, sometimes closes the program. How do I catch the problem before it force closes?

The query checks the remaining stocks by getting the sum of all the inputted stocks and subtracting it from the products sold, transferred to another branch and those that got damaged. So every time they search a product, it goes through 4 tables (Inventory, Sales, Transferred, Damaged) to get the stocks and 4 more tables to get the product's description (Product, Category, Subcategory, Supplier).

So going back, how do I log the error before the application closes? I'm thinking of getting the form closed event but how do I log it only if it crashes?

EDIT 1: I always put try catch with message box to all my methods. The application doesn't pop up any messages before it closes.

SELECT p.Id,p.Product_Name Product,p.Description,
c.Category_Name Category,sc.Subcategory_Name Subcategory,s.Supplier_Name Supplier,p.Selling_Price `Unit Price`,
i.Stocks,s.Sales,i.Stocks - IFNULL(s.Sales, 0) - IFNULL(t.Transfer, 0) - IFNULL(d.Damage, 0) AS Remaining

FROM (SELECT Id, Product_Name, Description, Selling_Price, Category_Id, Subcategory_Id, Supplier_Id FROM product WHERE enable_flag = 1) p

LEFT OUTER JOIN(SELECT product_id, COALESCE(SUM(quantity), 0) AS Stocks FROM inventory WHERE enable_flag = 1 GROUP BY product_id) i
ON p.Id = i.product_id

LEFT OUTER JOIN(SELECT product_id, COALESCE(SUM(quantity), 0) AS Sales FROM sales_detail WHERE enable_flag = 1 GROUP BY product_id) s
USING(product_id)

LEFT OUTER JOIN(SELECT product_id, COALESCE(SUM(transfer_quantity), 0) AS Transfer FROM stock_transfer WHERE enable_flag = 1 GROUP BY product_id) t
USING(product_id)

LEFT OUTER JOIN(SELECT product_id, COALESCE(SUM(damaged_quantity), 0) AS Damage FROM damaged_product WHERE enable_flag = 1 GROUP BY product_id) d
USING(product_id)

JOIN Category c ON p.Category_Id=c.Id
JOIN Subcategory sc ON p.Subcategory_Id=sc.Id
JOIN Supplier s ON p.Supplier_Id=s.Id;

EDIT 2:

Here's my button code ( Variables.dgvSearchItemsDataSource is equivalent to the posted query):

private void btnSearch_Click(object sender, EventArgs e)
{
    dgvSearchItems.DataSource = dbConnect.DatabaseToDatagrid(Variables.dgvSearchItemsDataSource + " WHERE p.Product_Name LIKE '" + cmbSrchProd.Text + "%'");
    if (dgvSearchItems.Rows.Count != 0)
    {
        this.dgvSearchItems.Columns[1].Frozen = true;
        this.dgvSearchItems.Columns[2].Frozen = true;
        this.dgvSearchItems.Columns[0].Visible = false;
        this.dgvSearchItems.Columns[7].Visible = false;
        this.dgvSearchItems.Columns[8].Visible = false;
    }
    txtQuantity.Focus();
}

The method I use to connect to my database:

private bool OpenConnection()
{
    try
    {
        connection.Open();
        return true;
    }
    catch (MySqlException ex)
    {
        switch (ex.Number)
        {
            case 0:
                myNotification = new frmNotifOk();
                myNotification.Show("Cannot connect to server.");
                break;

            case 1045:
                myNotification = new frmNotifOk();
                myNotification.Show("Invalid username/password, please try again.");
                break;
        }
        return false;
    }
}

Answer 1

It seems that although you think you put try/catch blocks around every call, somewhere an unhandled exception is thrown.

I think https: System.AppDomain.UnhandledException might help.

This event provides notification of uncaught exceptions. It allows the application to log information about the exception before the system default handler reports the exception to the user and terminates the application. If sufficient information about the state of the application is available, other actions may be undertaken — such as saving program data for later recovery

Handling this event will give you the opportunity to log the problem before the program closes.

usage:

static class Program
{
    private static MyLogger logger = new MyLogger();

    static void Main(string[] args)
    {
        AppDomain.CurrentDomain.UnhandledException += UnhandledException;

        ...
    }

    static void UnhandledException(object sender, UnhandledExceptionEventArgs e)
    {
        var exc = e.ExceptionObject as Exception;
        if (exc != null)
        {   // log the exception
            logger.LogException(exc);
        }
        // Problem is logged, Can't continue, so quit the application:
        Environment.Exit(-1);
    }

Answer 2

Add a try catch block around the code you are using to execute the query

        try
        {
            // Execute query
        }
        catch (Exception)
        {
           // Exception handling
            throw;
        }