.NET : How to solve System.Data.Entity.DbContext Compiler Error

Recently I wanted to get a better understanding of what Entity Framework is all about. I looked for the blog posts dedicated to this topic and I found one such post with a concrete example. I was eager to test the code, so I created a project in Visual Studio Express but to my surprise, I was not able to successfully build the project as it gave me System.Data.Entity.DbContext Compilation Error.

It took me a while before I managed to get rid of this annoying error and I want to share the solution that worked for me so that it might also help others with the same issue.

The compilation error I was getting was this:

The described solution in this post consists of 3 steps. You might not need to go through all them. I suggest that after each step try to build your project just to check if error still persists.

To solve the problem, I had to do the following:

1. add a reference to the EntityFramework.dll file in the project.

   First I tried the most probable cause of the compiler error, which is to add that missing reference of the EntityFramework assembly. To do that, you do the steps described below:

   • On the solution explorer, under your project, right-click references and click on Add Reference

     

     Alternatively you can go to Project menu and select Add reference.

   • Add Reference window will appear and under .NET tab, find EntityFramework. It should be located in the beginning of the list.
     
   • Select the EntityFramework from the list and click OK. Now go to step 3.

   The problem for me was that I was not able to find EntityFramework in the list, so I tried the next step.

2. Manually add EntityFramework from GAC to the references Assemblies for .NET

   Since I was unable to find the EntityFramework assembly in step 1, I decided to manually add it from GAC (Global Assembly Cache) and hoped this would solve the problem of adding the assembly reference to my project.

   • Locate the EntityFramework.dll from Global Assembly Cache folder and copy it to the Reference Assemblies folder.
   • Now try adding the reference as described in step 1.
   For locations of the folders in Win7 x64, check the table below:

   Global Assembly Cache Folder

   C:\Windows\Microsoft.NET\assembly\GAC_MSIL\EntityFramework\v4.0_4.1.0.0__b77a5c561934e089

   Reference Assemblies for .NET 4.0 folder

   C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0

   After completed this step I was able to add EntityFramework reference to the project but the error still persisted.

3. Modify web.config file

   Then I opened web.config file and modified it by adding EntityFramework assembly into <assemblies> tag.

• Locate <assemblies>tag and add following additional item in the list

  <add assembly=”EntityFramework, Version=4.1.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089″/>
  

After doing all 3 steps, the project was finally built successfully.

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