wpf dataGrid sum cell with entities

Question

I display dataGrid in WPF and entity framework, column 2 has a price per unit column 3 has the quantity (column 4 has the discount), I want column 5 will be the summary. My question is how I can capture the third column and calculate the change to the total column

Here is the code How do I display the data

          <DataGrid.Columns>
            <DataGridComboBoxColumn x:Name="ddd"  Header="Expenses" Width="*" SelectedValueBinding="{Binding Path=ExpensesId}" DisplayMemberPath="ExpensesName" SelectedValuePath="ExpensesTypeId"/>
            <DataGridTextColumn Header="price" Width="*" Binding="{Binding Path=Expenses.PricePorEach}"/>
            <DataGridTextColumn Header="quantity" Width="50"  Binding="{Binding Path=Quantity}"/>
            <DataGridTextColumn Header="discount" Width="*" Binding="{Binding Path=Discount}"/>
            <DataGridTextColumn Header="Total" Width="*" Binding="{Binding Path=Total}"/>
        </DataGrid.Columns>
    </DataGrid>

      ContractorEntities ce = new ContractorEntities();
    public MainWindow()
    {
        InitializeComponent();
        BindData();
    }
    private void BindData()
    {
        var dataSource = new  ObservableCollection<Jobs>(ce.Jobs);
        dataSource.CollectionChanged += CollectionChanged;
        dg.ItemsSource = dataSource;
        dg.DataContext = dataSource;

    }
    private void CollectionChanged(object sender,  NotifyCollectionChangedEventArgs e)
    {
        if (e.Action == NotifyCollectionChangedAction.Add)
            foreach (Jobs job in e.NewItems)
                  ce.Jobs.Add(job);

        else if (e.Action == NotifyCollectionChangedAction.Remove)
            foreach (Jobs jobin e.OldItems)
                ce.Jobs.Remove(job);
    }
    private void saveButton_Click(object sender, RoutedEventArgs e)
    {
        ce.SaveChanges();
    }
    [NotMapped]
    public decimal? Total
    {
        get
        {
            return (Price * Quantity) - Discount;
        }
        set { }
    }

    public void OnDiscountChanged()
    {
        base.OnPropertyChanged("Total");//This line is not known
    }

    public void OnPriceChanged()
    {
        base.OnPropertyChanged("Total");//This line is not known
    }

    public void OnQuantityChanged()
    {
        base.OnPropertyChanged("Total");//This line is not known
    }

}

I tried several ways, but no results

Thanks in advance for help

Answer 1

If you are using CodeFirst to create your entities

Since you are using entities, you can create an unmapped (use the [NotMapped] attribute) property in your entity class that computes the values and bind a column to that property. Since Entity classes implement INotifyPropertyChanged by default, everything should perform without much more work, although you may need to put a PropertyChangedEventHandler call on the other three (Price, Quantity, Discount) to tell the UI to update the value of Total.

[NotMapped]
public int Total
{
    get
    {
        return (Price * Quantity) - Discount;
    {
}

Since you are not going to be setting the Total in code, the property is ReadOnly.

If you are using an EDMX and designer to create your entities

Since you are using an EDMX (through the designer), you will need to add the property via a partial class.

1. Create a new class named the same as the Entity that you want to modify (Job in this case I think).
2. Mark the class declaration as partial. In this case, you can now add methods to a generated class.
3. Add the above Total property (editing the formula as necessary).

4. You will likely have to override the PriceChanged, QuantityChanged, and DiscountChanged methods and add a property changed event handler call specifying the total property (e.g. base.OnPropertyChanged("Total");) so that the UI knows to update.

   public partial class Job
   {
       public void OnDiscountChanged()
       {
           base.OnPropertyChanged("Total");
       }
   
       public void OnPriceChanged()
       {
           base.OnPropertyChanged("Total");
       }
   
       public void OnQuantityChanged()
       {
           base.OnPropertyChanged("Total");
       }
   }
   

Update

I got your solution, and looked at it. Your entities are generated via T4 template. I don't have much experience with those, but for the most part, the answer above in the section "If you are using an EDMX and designer to create your entities" still sort of applies. You need to modify the the T4 template to implement property changed notifications in such as way as you can get to the property changed method, and put the Total property (without the NotMapped attribute) in your partial class. The answer supplied here looks like it is relevant and correct (based on what knowledge I have about the subject).