Progress® Telerik® Reporting R2 2017

Maintaining the lifecycle of the Context with the EntityDataSource component

This section discusses how to maintain the lifecycle of the ObjectContext/DbContext when using the EntityDataSource component. The provided examples and code snippets assume an existing Entity Data Model of the Adventure Works sample database with the following structure:

One possible approach to connect to an Entity Data Model without using the EntityDataSource component is to create a custom business object with a method that retrieves the necessary entities for the report. The sample code below defines a method that retrieves information about all products:

public class SampleBusinessObject
{
    public System.Collections.Generic.List<Product> GetProducts()
    {
        using (AdventureWorksEntities context = new AdventureWorksEntities())
        {
            return context.Products.ToList();
        }
    }
}

Then you can use ObjectDataSource to connect to that business object, as shown in the following code snippet:

var objectDataSource = new Telerik.Reporting.ObjectDataSource();

objectDataSource.DataSource = typeof(SampleBusinessObject);
objectDataSource.DataMember = "GetProducts";

var report = new Report1();

report.DataSource = objectDataSource;

The problem with this approach is that it is not guaranteed to work in all possible scenarios. Simple expressions accessing primitive properties of the Product entity might work as expected:

=Fields.Name

However, let us consider the following expression that is intended to obtain the category of a given product:

=Fields.ProductSubcategory.ProductCategory.Name

The above expression relies upon the lazy loading mechanism of the ADO.NET Entity Framework to obtain the ProductSubcategory entity for the current Product entity via the corresponding relation property, and then the ProductCategory entity for the current ProductSubcategory entity. This is not guaranteed to work because the ObjectContext/DbContext is already destroyed when evaluating the expression, so lazy loading is no longer possible. One of the greatest advantages of the EntityDataSource component is that it can maintain the lifecycle of the ObjectContext/DbContext automatically, so scenarios like the previous one are guaranteed to work as expected. When specifying a Type for the Context property, EntityDataSource creates internally a new instance of the ObjectContext/DbContext with the given type, keeps it alive for the duration of the report generation process, and then destroys it automatically when it is no longer needed by the reporting engine. The following code snippet accomplishes the previous task with the help of the EntityDataSource component:

var entityDataSource = new Telerik.Reporting.EntityDataSource();

entityDataSource.Context = typeof(AdventureWorksEntities);
entityDataSource.ContextMember = "Products";

var report = new Report1();

report.DataSource = entityDataSource;

If you have already implemented your own mechanism for maintaining the lifecycle of the ObjectContext/DbContext you can continue using the EntityDataSource component. In this case however you need to specify a live instance of your ObjectContext/DbContext to the Context property as demonstrated here:

var entityDataSource = new Telerik.Reporting.EntityDataSource();
var context = new AdventureWorksEntities();

entityDataSource.Context = context;
entityDataSource.ContextMember = "Products";

var report = new Report1();

report.DataSource = entityDataSource;

// You have to dispose the Context explicitly when done with the report.
context.Dispose();