Implementing Inheritance with the Entity Framework in an ASP.NET MVC Application (8 of 10)http://www.asp.netWed, 03 Oct 2012 13:03:35 GMTumbracoComments for Implementing Inheritance with the Entity Framework in an ASP.NET MVC Application (8 of 10)enComment Posted by timheffhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationMon, 09 May 2011 13:55:15 GMT00000000-0000-0000-0000000013111There seems to be a problem in the Instructor Index.cshtml after implementing these changes and attempting to test. I get the "There is already an open DataReader associated with this Command which must be closed first." error in the view at this line...

@if (item.OfficeAssignment != null)

I downloaded the completed application to verify that the same error occurs with that solution and it does.

]]>Comment Posted by timheffhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationMon, 09 May 2011 15:30:12 GMT00000000-0000-0000-0000000013113I found I just had to add 'MultipeActiveResultSets=true' to my connection string. I'm using SQL Server Developer Edition on my machine. For anyone else who might have the same scenario (not using SQL Server Compact), here is my full connection string...<add name="SchoolContext" connectionString="Data Source=localhost;Initial Catalog=ContosoUniversity; Integrated Security=SSPI; MultipleActiveResultSets=True " providerName="System.Data.SqlClient"/>

]]>Comment Posted by pseudo70http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationFri, 20 May 2011 13:22:38 GMT00000000-0000-0000-0000000013231Your advice "In Instructor.cs, derive the Instructor class from the Person class, change the InstructorID property to PersonID, and remove the key and name fields. The code will look like the following example:" reflects not the given example code. There is no PersonID in this example code. Should Instructor.cs now contain the PersonID foreign key or not? The same for the Person.cs class.

]]>Comment Posted by pseudo70http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationFri, 20 May 2011 13:27:48 GMT00000000-0000-0000-0000000013232I mean, the same for the Student.cs class. Not Person.cs class.

]]>Comment Posted by tdykstrahttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationSun, 22 May 2011 11:14:47 GMT00000000-0000-0000-0000000013244@pseudo70 - You are correct, thanks for pointing that out. I will remove the phrase "change the InstructorID property to PersonID".

]]>Comment Posted by obdensehttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationFri, 03 Jun 2011 17:18:50 GMT00000000-0000-0000-0000000013384timheff - Thank you for your postings. I encountered the exact issue using SQL Server Express Edition 10.50.1600.1. I added the MultipleActiveResultSets=true and all was well.

]]>Comment Posted by dreamscourgehttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationThu, 16 Jun 2011 12:26:39 GMT00000000-0000-0000-0000000013543@timheff Thanks again, had the same problem too. SQL Server 2008 R2

]]>Comment Posted by chicachanhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationThu, 30 Jun 2011 22:07:58 GMT00000000-0000-0000-0000000013648How can I "Next, perform a global change (all files in the project) to change InstructorID to PersonID",Please explain its detail? thank you.

]]>Comment Posted by tdykstrahttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationMon, 04 Jul 2011 14:50:28 GMT00000000-0000-0000-0000000013686@chicachan - Type control/h to get the change dialog in Visual Studio, and you'll see that one of the options is to make the specified change in all files.

]]>Comment Posted by hong6http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationMon, 04 Jul 2011 21:43:47 GMT00000000-0000-0000-0000000013691great Tutorial!

]]>Comment Posted by TheGDizzohttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationFri, 23 Sep 2011 17:28:42 GMT00000000-0000-0000-0000000014254What was the specific act we did in this tutorial that signalled to the Entity Framework the need to add the "Discriminator" column to our [Person] table. Was it the mere change of inheriting from Person.cs? Like when [Instructor] and [Student] tacked on the inheritance clause of " : Person" to the "public class Instructor : Person" and "public class Student : Person" statements?

]]>Comment Posted by tdykstrahttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationThu, 06 Oct 2011 14:44:49 GMT00000000-0000-0000-0000000014343@TheGDizzo - Yes, that is all EF needs to determine that it needs a discriminator column.

]]>Comment Posted by TekzMekzhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationSat, 08 Oct 2011 17:17:40 GMT00000000-0000-0000-0000000014370Please help!!! I manually followed all the steps since I do not want to implement the last two tutorials, so I don't want to work backwards from the downloadable full demo. It would be great if a download point was made available at the end of every tutorial. Anyway... I had everything until I got to the step where you instruct us to do the following:

"Next, perform a global change (all files in the project) to change InstructorID to PersonID and StudentID to PersonID. Make sure that this change is case-sensitive."

Now I cannot access the Instructors page. It stops in the line:

"@foreach (var item in Model.Instructors) {"

with the following error:

"The ResultType of the specified expression is not compatible with the required type. The expression ResultType is 'Transient.reference[ContosoUniversity.Models.Person]' but the required type is 'Transient.reference[ContosoUniversity.Models.Instructor]"

Thanks for an excellent tutorial.

]]>Comment Posted by tdykstrahttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationWed, 19 Oct 2011 22:09:32 GMT00000000-0000-0000-0000000014461@TekzMekz - Double-check the changes in the entities themselves, this does not sound like a problem with renaming the ID fields. Althought the download project has other changes in it, you can still compare most of the files, such as the entity classes to see what you might have missed.

]]>Comment Posted by websmithhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationThu, 08 Mar 2012 16:20:36 GMT00000000-0000-0000-0000000015067I, too, am having the problem with the Datareader. However, the change suggested does not fix it for me. So what is causing this error to happen in the first place? It happens, as mentioned, when hitting:

@if(item.OfficeAssignment != null)

In the Instructors\Index.cshtml view.

Any other suggestions? My database is on SQL Server 8.00.2055

]]>Comment Posted by tdykstrahttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationFri, 09 Mar 2012 15:06:16 GMT00000000-0000-0000-0000000015080@websmith - I recommend submitting that to the ASP.NET forum or to StackOverflow.com. For the next release of the tutorial we may add a sidebar about changes needed for other versions of SQL Server; if you find a solution and post it here we'll make sure it gets added to the tutorial.

]]>Comment Posted by redcolinhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationThu, 12 Apr 2012 12:09:24 GMT00000000-0000-0000-0000000015305@websmith - there is a typo in timheff's op - "Multiple" had the second "L" missing - perhaps this will solve your issue as it did for me.

]]>Comment Posted by mjesonhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationMon, 07 May 2012 20:47:50 GMT00000000-0000-0000-0000000015466This TPH-over-TPT recommendation makes me cautious to apply MVC in data intensive production environment.

I come from Oracle where dealing with 100 millions of records with hundreds columns is a performance hell unleashed. Index stops working since every query is a full-table-scan due to large data retrieval. TPT is a way to divide this huge dataset into smaller records with less columns.

Ideally speaking, MVC should only be dependent upon the actual size of dataset, regardless of TPH/TPT.

]]>Comment Posted by jsiahaanhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationTue, 15 May 2012 21:18:05 GMT00000000-0000-0000-0000000015514@websmith - Has the problem with "@if(item.OfficeAssignment != null) In the Instructors\Index.cshtml view" been solved?

I have the same problem too using ASP.NET MVC 4 Beta version, Ef 5.0 pre release, VS 2010, SQL Server 2012 Express Edition on Windows Server 2008 R2. The only problem I have is the same with you.

I also tried several time using ASP.NET MVC 4 beta, VS 11 Beta, EF 4.1 and EF 4.3 and EF 5.0, Win 8 Consumer preview and I can not create all Controllers but only CourseController

]]>Comment Posted by spacemishkahttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationFri, 22 Jun 2012 07:54:51 GMT00000000-0000-0000-0000000015822I am getting a parsererror when i try to run my App after the changes of this part.

Line 1: <%@ Application Codebehind="Global.asax.cs" Inherits="ContosoUniversity.MvcApplication" Language="C#" %>

Whats wrong?

]]>Comment Posted by tdykstrahttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationFri, 22 Jun 2012 17:40:48 GMT00000000-0000-0000-0000000015826@spacemishka - The easiest way to troubleshoot is to download the completed application, then compare the code there with what you created by following the tutorial. You might have mistyped something or omitted a step.

]]>Comment Posted by Takumihttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationTue, 03 Jul 2012 10:22:44 GMT00000000-0000-0000-0000000015899@jsiahaan, @websmith

I have the same problem and found an answer in this thread: social.msdn.microsoft.com/

After adding MultipleActiveResultSets=True; to the connection string the problem is solved. This may lead to other problems, but for now it's working. :-)

]]>Comment Posted by mudasir.khanhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationMon, 16 Jul 2012 13:40:33 GMT00000000-0000-0000-0000000015986SuperB, Thanks for such a nice and excellent way of explanation

]]>Comment Posted by aaronnewtonhttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationTue, 18 Sep 2012 08:59:29 GMT00000000-0000-0000-0000000016454If you are getting the "There is already an open DataReader " error, please take a look at stackoverflow.com/

For InstructorController.cs I added .ToList() like so:

viewModel.Instructors = db.Instructors

.Include(i => i.Courses.Select(c => c.Department))

.ToList()

.OrderBy(i => i.LastName);

Do this anywhere we deleted '.Include(i => i.OfficeAssignment)'. This appears to have fixed the problem.

]]>Comment Posted by gagouchehttp://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/implementing-inheritance-with-the-entity-framework-in-an-asp-net-mvc-applicationWed, 03 Oct 2012 13:03:35 GMT00000000-0000-0000-0000000016569I am a little confused here. You explained the difference between TPH and TPT. Since you are going to use TPH, I expected the instructor and student class to be completely gone. Instead they inherited the base class. Isn't that still TPT, or were you only referring to the database and not the actuall class design?

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