Entity data model designer won't open the edmx file

Solution 1:

FOR Visual Studio 2017, 2019

I searched for the solution but come up with the installation of some NUGET packages and Extensions, nothing worked out.

Solution (Missing Entity Framework on Visual Studio)

1. I searched for Visual Studio Installer on my machine and opened it.
2. Under Visual Studio Professional 2017.
3. I clicked on More to see more options. I selected Modify
4. Select Individual Components (Second Tab)
5. Check Entity Framework Under SDKs, libraries, and framework
6. and then click Modify EDMX file will open after the process gets completed.

Solution 2:

This has happened to me a few times, usually when pulling a solution out of subversion. Rebuilding the project has always fixed the issue for me.

Solution 3:

I also encounter that annoying screen. No, I do NOT want to edit my model in XML... I want the pretty designer! In my case I added a table which did not have a primary key. To fix...

1. Open the edmx in XML

2. Delete the erroneous table. It should be well defined with an "<-- ERROR" comment.

3. Clean and Rebuild.

4. Close and re-open Visual Studio (yes, it's annoying but necessary)

5. Rebuild one more time, then open your edmx file. Should open the designer fine.

Hope this helps.