Threading and Saving Data with LINQ to SQL

In our last post we looked at the actual calculations of the amortization.

Threading

Depending on the machine and the values the user has specified the calculation and displaying of the mortgage could lag. 100-200 milliseconds is the threshold before a user notices lag. We want the transition from MortgageHome Page to MortgageReport Page to be as seamless as possible while still immediately amortizing the mortgage. In order to accomplish this we need to run the calculations in their own worker thread, outside the UI thread.

In the MortgageReport page we set up the following threading.

//start a worker thread so it does not bog down the gui
private void Amortize()
{
    BackgroundWorker worker = new BackgroundWorker();

    worker.DoWork += delegate(object s, DoWorkEventArgs args) 
    {
        args.Result = RunAmortize(); 
    }; 
    worker.RunWorkerCompleted += delegate(object s, 
        RunWorkerCompletedEventArgs args) 
    {
        theMI = (MonthIteration)args.Result;
        SetGridData();
    }; 
    worker.RunWorkerAsync();
}

private MonthIteration RunAmortize()
{
    MonthIteration thisMI = new MonthIteration(m);
    return thisMI;
}

In the last post we saw how the MonthIteration class constructor ran all of our calculations for us. As soon as the first line in RunAmortize is complete so are our calculations.

I choose a BackgroundWorker due to it's straight forward approach of assignment to clearly spelled out events. In this case we are creating 2 anonymous delegates; one to start the thread and do the work and one to notify the thread that the work is complete. There are other events for updating progress and when dispose on the component is called. This could have easily just been pulled into its own class. However, since it's relatively uninvolved I kept it in the MortgageReport Page.

Saving Data with LINQ to SQL

The last piece of the puzzle is to save the data to the database for use later on. Because we put the legwork in for LINQ to SQL in a previous post, all we need to do now is use that code to save the data.

private bool IsValid(ref String em, bool checkForName)
{
    List<String> errors = new List<string>();

    if (checkForName && m.Name == null)
        errors.Add("You must specify a Name.");
    else if (checkForName && m.Name.Trim() == String.Empty)
        errors.Add("You must specify a Name.");
    if (m.Principal <= 0)
        errors.Add("You must specify Principal Amount greater than $0.00.");
    if (m.Term <= 0)
        errors.Add("You must specify a Loan Term greater than 0.");
    if (m.InterestRate <= 0)
        errors.Add("You must specify an Interest Rate.");
    em = String.Join(Environment.NewLine, errors);

    if (errors.Count > 0)
        return false;
    else
        return true;
}

Before we can even attempt to save we need to validate all the necessary values. In this case we pass in a string by ref to ensure the calling method can show the user the problems encountered.

private void SaveB_Click(object sender, RoutedEventArgs e)
{
    String em = "";
    if (!IsValid(ref em, true))
    {
        MessageBoxResult result = MessageBox.Show((Window)this.Parent, 
            em, "Error", MessageBoxButton.OK, MessageBoxImage.Error);
    }
    else
    {
        m.Date = DateTime.Now;

        if (isNew)
        {
            if (DBApi.DB.mortDB.Mortgage.Count() > 0)
            {
                m.Key = (from thisMort in DBApi.DB.mortDB.Mortgage
                            select thisMort.Key).Max() + 1; 
            }
            else
                m.Key = 0;
            DBApi.DB.mortDB.Mortgage.InsertOnSubmit(m);
        }

        DBApi.DB.mortDB.SubmitChanges();
        isNew = false;
    }
}

If the values are invalid we give the user immediate feedback in the form a error MessageBox.

One problem that crept up on me when I was working on this is the defaulting of the Key to 0. Since Key 0 already exists in the database, we are now no longer allowed to add new records. To get around this I simply did a quick LINQ to SQL query to find the Max Key and incremented it by 1.

InsertOnSubmit is the same as the insert command in T-SQL. SubmitChanges looks for updates, inserts or deletions and sends them to the database.

That's it! We now have a fully functional Mortgage Calculator that looks pleasant, is somewhat dynamic to the users preferences, stores UI state and gives the user a lot of useful information.

Future Improvements

When coding it's almost impossible to not notice improvements. The following are some features I would like to see in the Mortgage Calculator in the future.

1. An installer package
2. In-grid adjustments
3. Better color schema
4. More detailed stats on values such as
1. Total insurance paid
2. Total taxes paid
5. Home page selection memory
6. Years and months term input fields instead of just months
7. PMI
8. Date tracking by listing the start date
9. Monthly payment date to adjust interest and principal to the day payment was received
10. Application Icon
11. MortgageHome showing more details about each Mortgage
12. Start amortizing in the middle of the year and figure costs accordingly like Tax increasing at the end of the year, which might be 4 months into the loan.
13. Graphs and charts
14. User accounts
15. User account summaries of the user's entire portfolio

Download the Code Here