The type or namespace name 'DbContext' could not be found

Question

I am VERY new to ASP.NET MVC (3) and am having a hard time resolving a build error in Visual Studio:

The type or namespace name 'DbContext' could not be found (are you missing a using directive or an assembly reference?)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel.DataAnnotations;
using System.Data.Entity;

namespace MyProjectName.Models
{   
    public class MachineModel
    {
        // name
        [Required]
        [Display(Name = "Nom de la machine")]
        public string Name { get; set; }

        // IP
        [Required]
        [RegularExpression(@"(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)",
           ErrorMessage = "Donnez une adresse IPv4 valide.")]
        [Display(Name = "Adresse IP de la machine")]
        public string IP { get; set; }
    }

    public class MachineDbContext : DbContext
    {
        public DbSet<MachineModel> Machines{ get; set; }
    }
}

The two errors I am getting are:

• The type or namespace name 'DbContext' could not be found (are you missing a using directive or an assembly reference?)
• The type or namespace name 'DbSet' could not be found (are you missing a using directive or an assembly reference?)

What am I missing?

Solution 1

I had the same issue. Turns out, you need the EntityFramework.dll reference (and not System.Data.Entity).

I just pulled it from the MvcMusicStore application which you can download from: http://mvcmusicstore.codeplex.com/

It's also a useful example of how to use entity framework code-first with MVC.

Solution 2

You need to reference the System.Data.Entity assembly in your project, or install the EntityFramework NuGet package, which will setup everything for you.

Solution 3

Just a quick note. It is DbContext, not DBContext. i.e. with a lowercase 'B'. I discovered this because I had the same problem while intelesense was not working until I tried typing the full name space System.Data.Entity... and name and finally it suggested the lowercase 'b' option:-

System.Data.Entity.DbContext

Solution 4

I had the same problem using VS2010. I know this isn't really an answer. I just thought it might help someone. I resolved it by using the fully qualified name for DBContext.

Instead of

public class MachineDbContext : DbContext

I used

public class MachineDbContext : System.Data.Entity.DbContext

and rebuilt the project. Suddenly VS was happy, and I was even able to remove the fully qualified name, and just use DBContext.

Solution 5

I had the same issue... Installing the EF from Package Manager Console worked for me

the command was: Install-Package EntityFramework

View more solutions

Comments

[Ed Chapel]

Did you add the Entity Framework Code First reference using NuGet? That might be the easiest way to resolve references.

[Chris]

o.k. - under the Solution Explorer Tree I did a right-click on References -> Add Library Package Reference -> EFCodeFirst -> Install. Is this what you were suggesting? After following these steps I still have the same problem.

[Chris]

I have meanwhile updated the MVC 3 Tools to the newest version, and created a tutorial project following asp.net/mvc/tutorials/getting-started-with-mvc3-part4-cs. In that project, I don't have this problem, but I can't get DbContext to be accepted in my older project, despite the suggestions made here and by Darin below...

[redwards510]

VS2017, EF6, Close the solution. Reopen solution. It now properly recognizes DbContext.

[Zahid Hasan]

Open the Package Manager Console. Select Tools > NuGet Package Manager > Package Manager Console. In the Package Manager Console, enter the following command: install-package EntityFramework

[Steve Smith]

Why is this question closed? Thank goodness there are some answers here that helped, before an overzealous mod closed it.

[Chris]

Darin, could you explain how one would do this?

[Darin Dimitrov]

@Chris Dickinson, right click on the References item in the project and select Add Reference.... Then in the .NET tab, select System.Data.Entity. And if you want to use NuGet, right click on the References item and then select Add Library Package Reference... and in the Online tab, search for EntityFramework.

[Chris]

I followed both of your steps, but the problem still persists...

[Amitd]

did u use NuGet to install EntityFramework?It creates a folder "packages" along side your Solution directory. You will find the "EntityFramework.4.1.10331.0" folder inside it.Within "Libs" folder you will find "EntityFramework.dll" .Add reference to it using Browse tab and select the above dll. see my answer below.. i did the same.

[mtazva]

Required assembly reference is EntityFramework.dll, not System.Data.Entity. I had to do the full Entity Framework 4.1 install to get it - NuGet did not pull the appropriate assembly for me.

[gerryLowry]

this was my experience; the EntityFramework.dll for 4.2.0.0 was not present even though the vs2010 Package Manager claimed I had 4.2.0.0 installed. With my project open in vs2010, running the install command via Tools, Library Package Manager, Package Manager Console added the reference to EntityFramework automatically and my subsequent build succeeded. thnx @Shahzad!

[NoChance]

Thanks for your help. I hope Microsoft would one day make installation of their own software on their windows easier! It is amazing how many places one has to go to to figure what is needed and how they all fit together. NuGet, MS Download site, Message boards, books,....very productive time indeed.

[kingdango]

Your best bet is to use NuGet (package manager) to pull Entity Framework (et al) into your projects.

[Nate-Wilkins]

Those 3 line actually inside the class?

[Peter Gluck]

I selected TOOLS > Library Package Manager > Package Manager Console in VS2012 and typed install-package EntityFramework at the prompt. Worked perfectly.

[Bedouin]

some times you need to restart visual studio to make the installation works. this was my case.

[Piotr Kula]

You can use the Nuget Manage Packages for Solutions. Find EntityFramework and click Manage. There will be check boxes to where it is installed next to each project. Make sure you are using the version of EF you need. You can use multiple versions in the same solution, for various reasons.

[F0r3v3r-A-N00b]

I've been going through all the references regarding System.Data.Entity only to discover that the problem was the uppercase "B". +1

[user2862542]

Open Package Manager Console and paste in: Install-Package EntityFramework

[Paceman]

Yes this solved it. Provided "Install-Package EntityFramework" step was done. Thanks, +1.

[wickd]

I had a similar issue after installing the entity framework from Nuget. Rebuilding the solution seemed to sort this out...

[brntsllvn]

System.Data.Entity did the trick for me

[Kevin]

Only adding the reference to System.Data.Entity still left me with DbContext not being recognized. Also following @PeterGluck his comment worked for me. Small update for VS2017: >Tools >NuGet Package Manager >Package Manager Console and type install-package EntityFramework.

[Fabio S.]

This worked for me, but it seems very bizarre that I need to fully qualify the DbContext even though the using statement is already in place. Does anyone have any insight on why this is happening?

[eden m]

or Microsoft.EntityFrameworkCore.DbContext - worked for me :)