How to: Query Objects with Table-per-Type Inheritance
This topic shows how to execute a polymorphic query by using the OfType operator.
To run the code in this example
Add the School Model to your project and configure your project to use the Entity Framework. For more information, see How to: Use the Entity Data Model Wizard.
Modify the conceptual model to have table-per-type inheritance by following the steps in Walkthrough: Mapping Inheritance - Table per Type.
Example
The following example uses the OfType method to get and display a collection of OnsiteCourses and a collection of OnlineCourses from a collection of Courses. OnsiteCourses and OnlineCourses are specific types of Courses.
Try
Using context As New SchoolEntities()
Dim departmentID = 7
' Get courses for the department with id 7.
Dim courses As IQueryable(Of Course) = _
context.Departments.Where(Function(d) d.DepartmentID = departmentID).SelectMany(Function(d) d.Courses)
Console.WriteLine("All the courses for the selected department.")
For Each course As Course In courses
Console.WriteLine("CourseID: {0} ", course.CourseID)
Next
Dim onlineCourses = courses.OfType(Of OnlineCourse)()
Console.WriteLine("Online courses only for the selected department.")
For Each onlineCourse As OnlineCourse In onlineCourses
Console.WriteLine("CourseID: {0} ", onlineCourse.CourseID)
Next
Dim onsiteCourses = courses.OfType(Of OnsiteCourse)()
Console.WriteLine("Onsite courses only for the selected department.")
For Each onsite As OnsiteCourse In onsiteCourses
Console.WriteLine("CourseID: {0} ", onsite.CourseID)
Next
End Using
Catch e As System.Data.MappingException
Console.WriteLine(e.ToString())
Catch e As System.Data.EntityException
Console.WriteLine(e.ToString())
End Try
try
{
using (SchoolEntities context =
new SchoolEntities())
{
int departmentID = 7;
// Get courses for the department with id 7.
IQueryable<Course> courses = context.Departments
.Where(d => d.DepartmentID == departmentID)
.SelectMany(d => d.Courses);
Console.WriteLine("All the courses for the selected department.");
foreach (Course course in courses)
{
Console.WriteLine("CourseID: {0} ", course.CourseID);
}
var onlineCourses = courses.OfType<OnlineCourse>();
Console.WriteLine("Online courses only for the selected department.");
foreach (OnlineCourse onlineCourse in onlineCourses)
{
Console.WriteLine("CourseID: {0} ", onlineCourse.CourseID);
}
var onsiteCourses = courses.OfType<OnsiteCourse>();
Console.WriteLine("Onsite courses only for the selected department.");
foreach (OnsiteCourse onsite in onsiteCourses)
{
Console.WriteLine("CourseID: {0} ", onsite.CourseID);
}
}
}
catch (System.Data.MappingException e)
{
Console.WriteLine(e.ToString());
}
catch (System.Data.EntityException e)
{
Console.WriteLine(e.ToString());
}
See Also
Tasks
How to: Define a Model with Table-per-Type Inheritance