How do you update your LINQ queries and data visualization outputs when data changes?

1 Use deferred execution

One of the key features of LINQ is deferred execution, which means that the query is not executed until you iterate over the results. This allows you to write queries that are dynamic and responsive to data changes. For example, if you have a query that selects the top 10 products by sales from a database, you can use deferred execution to get the most recent data every time you access the query. To use deferred execution, you need to avoid methods that force immediate execution, such as ToList, ToArray, Count, or Sum. Instead, you can use IEnumerable or IQueryable as the return type of your query, and use foreach or LINQ methods to iterate over the results.

2 Use data binding

Another way to update your data visualization outputs when data changes is to use data binding. Data binding is a technique that connects a data source to a UI element, such as a chart, a grid, or a label. When the data source changes, the UI element automatically updates to reflect the new data. To use data binding, you need to implement the INotifyPropertyChanged interface in your data source class, and raise the PropertyChanged event when a property changes. Then, you need to set the DataContext property of your UI element to the data source object, and use the Binding markup extension to specify the property path. For example, if you have a class called Product with a property called Sales, and a chart called SalesChart, you can use data binding as follows:

public class Product : INotifyPropertyChanged
{
  private decimal sales;
  public decimal Sales
  {
    get { return sales; }
    set
    {
      sales = value;
      OnPropertyChanged(nameof(Sales));
    }
  }
  public event PropertyChangedEventHandler PropertyChanged;
  protected void OnPropertyChanged(string propertyName)
  {
    PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
  }
}
// ...
SalesChart.DataContext = product;
SalesChart.Series[0].ItemsSource = new Binding("Sales");        

3 Use refresh methods

Sometimes, you may need to explicitly refresh your LINQ queries and data visualization outputs when data changes. This may be the case when you use methods that cache the results, such as ToLookup, ToDictionary, or AsEnumerable. In this case, you can use the Refresh method of the Lookup, Dictionary, or Enumerable classes to re-execute the query and update the results. For example, if you have a lookup that groups products by category, and a grid that displays the lookup, you can use the refresh method as follows:

var productLookup = products.ToLookup(p => p.Category);
productGrid.ItemsSource = productLookup;
// ...
// Update some products in the database
// ...
// Refresh the lookup and the grid
productLookup.Refresh();
productGrid.Items.Refresh();        

4 Use reactive extensions

Another option to update your LINQ queries and data visualization outputs when data changes is to use reactive extensions. Reactive extensions are a set of libraries that enable you to write queries that react to events, such as data changes, user inputs, or timer ticks. Reactive extensions use the IObservable and IObserver interfaces to represent and subscribe to event streams. You can use LINQ methods to query, filter, transform, and aggregate event streams, and use data binding or other techniques to update your UI elements. For example, if you have an observable collection of products that emits events when items are added, removed, or updated, and a chart that displays the average sales by category, you can use reactive extensions as follows:

var productObservable = products.ToObservable();
var averageSalesByCategory = productObservable
  .GroupBy(p => p.Category)
  .SelectMany(g => g.Average(p => p.Sales).Select(a => new { Category = g.Key, Average = a }));
averageSalesByCategoryChart.DataContext = averageSalesByCategory;
averageSalesByCategoryChart.Series[0].ItemsSource = new Binding();        

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?