EF 5 Enable-Migrations : No context type was found

问题:

I have 4 projects :

Toombu.Entities : all models are there
Toombu.DataAccess: Mapping, Repository and ToombuContext
Toombu.Logique : Logic of my application
Toombu.Web : MVC 4 application. With all others DLL.

I tried to enable migration in Toombu.Web but i had this error :

No context type was found in the assembly

How can I enable migration ?

回答1:

use -ProjectName option in Package Manager Console:

Enable-Migrations -ProjectName Toombu.DataAccess -StartUpProjectName Toombu.Web -Verbose

回答2:

I am surprised that no one mentioned the obvious answer to this question: Entity Framework requires a context before enable-migrations will work. The error message the OP posted suggests that no context was found. Sure, it could be because the package manager console doesn't "see" the context--in which case the accepted answer is a possible solution (another solution is one I suggest, below). But a context must exist in the current project (assembly) before any other solutions will work.

What does it mean to have a context? It means that there must exist a class in your project that inherits from DbContext (in System.Data.Entity). Here is an example:

public class MyDbContext : DbContext
{
    public MyDbContext()
    {
    }
}

Be sure you use

using System.Data.Entity;

before the code above has access to the DbContext class and that you have used NuGet to get Entity Framework 4.1 or later for the current project.

If all along you had a context but the Package Manager Console just doesn't "see" it: In Visual Studio 2013 you don't have to use the -ProjectName switch. Instead, go to the Package Manager Console (it's available in the View | Other Windows list), and look at the two dropdowns that appear at the top of the Package Manager Console dockable window. The first dropdown is for Package Source; the second is for Default Project. If you dropdown the Default Project and select a project in your solution then whatever commands you issue in the Package Manager console will be executed against the selected project.

回答3:

Change the default project and choose the startup project from dropdown:

回答4:

If anyone is still facing this problem. I solved it by using the following command:

Enable-Migrations -ProjectName <YOUR_PROJECT_NAME> -ContextTypeName <YOUR_CONTEXT_NAME>

Don't forget to use the full path to your context name.

回答5:

You dbcontext is in Toombu.DataAccess So you should enable migrations in Toombu.DataAccess.

回答6:

I had to do a combination of two of the above comments.

Both Setting the Default Project within the Package Manager Console, and also Abhinandan comments of adding the -ContextTypeName variable to my full command. So my command was as follows..

Enable-Migrations -StartUpProjectName RapidDeploy -ContextTypeName RapidDeploy.Models.BloggingContext -Verbose

My Settings::

• ProjectName - RapidDeploy
• BloggingContext (Class Containing DbContext, file is within Models folder of Main Project)

回答7:

Change the default project to data access

change the default project dropdown in the package manager console to data access and give enable migrations...

Thats all success

回答8:

My problem was link----> problem1

I solved that problem with one simple command line

Install-Package EntityFramework-IncludePrerelease

After that, i needed to face with one more problem, something like:

"No context type was found in assembly"

I solve this really easy. This "No context" that mean you need to create class in "Model" folder in your app with suffix like DbContext ... like this MyDbContext. There you need to include some library using System.Data.Entity;

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


namespace Oceans.Models
{
    public class MyDbContext:DbContext
    {
        public MyDbContext()
        {
        }
    }
}

After that,i just needed this command line:

Enable-Migrations -ProjectName <YourProjectName> -ContextTypeName <YourContextName>

回答9:

Ensure you are using the same version of Entity Framework across all projects using the NuGet Package Manager.

Recent windows updates may have installed a newer version of Entity Framework into your active project.

Background: Around 16 Mar 2016, I started getting this error when trying to add migrations to a project where I had already enabled migrations and had successfully done migrations for.

I noticed that around March 10, a new stable version of Entity Framework 6 had been released.

If I specified the -ContextTypeName parameter in the enable-migrations command, I got an error indicating the migrations were already enabled.

Resolution:

1) Tools -> Nuget Package Manager -> Manage Nuget Packages for Solution

2) (Not sure if this step is necessary, but..) I updated my version of the Nuget Package Manager to the latest version. Also, after updating my version of Nuget Package Manager, I had to restart Visual Studio twice before the NuGet Command line would work properly.

3) Tools -> Nuget package Manager -> Manage Nuget Packages for Solution -> Search Installed packages -> Type Entity Framework

a. You may see more than one version of Entity Framework there.

b. Click Manage on each version of Entity Framework and ensure that your projects are using the SAME version of Entity Framework.

• Uncheck the version of Entity Framework that you are not using and for the version of Entity Framework you ARE using make sure it is checked across your projects that need it.

Again, as noted in step 2, I had to restart visual studio twice to get the NuGet Package Manager Console to work properly after updating my version of the NuGet Package Manager. I got an error starting the console the first time, and "exception calling createinstancefrom with 8 arguments could not load file or assembly EntityFramework" when running the enable-migrations command the second time.

Restarting visual studio seemed to resolve those issues, however.

回答10:

Thanks for the suggestions, I solved the problem by combining all the solutions here. At first I created the DbContext Model:

 public class MyDbContext: DbContext
    {
        public MyDbContext()
        {
        }
    }

After creating the dbcontext class, I ran the enable-migration command with the project Name: enable-migrations -ProjectName YourProjectName

回答11:

This error getting because of the compiler not getting 'Context' class in your application. So, you can add it manually by Add --> Class and inherit it with 'DbContext' Class For Example :

public class MyDbContext : DbContext
    {
        public DbSet<Customer> Customer { get; set; }
        public MyDbContext()
        {
        }
    }

回答12:

I have been getting this same problem. I have even tried above enable migrations even though I have already done. But it keeps giving same error. Then I had to use the force switch to get overcome this problem. I am sure this will help in someone else's case as well as its a possible work around.

After enabling migration with force, you should update your database (Make sure default project is set correctly). Otherwise you will get another problem like explicit migrations are pending.

Then just execute your add-migrations or any other commands, it should work.

Enable-Migrations -ProjectName <PROJECT_NAME> -ContextTypeName <FULL_CONTEXT_NAMESPACE.YOUR_CONTEXT_NAME> -force

回答13:

How to Update table and column in mvc using entity framework code first approach

1: tool > package manager console

2: select current project where context class exist

3: Enable migration using following command PM > enable-migrations

4: Add migration folder name using following command PM > add-migration MyMigrationName

4: Now update database following command PM > update-database

回答14:

namespace EntityFrameworkCodeFirst.Module
{
    public class MyDbContext: DbContext
    {
        public MyDbContext()
        {
        }
    }
}

And if you have Multiple project in one solution than you have to use below commands:-

Enable-Migrations -ProjectName EntityFrameworkCodeFirst

回答15:

Adding a class which inherits DbContext resolved my problem:

public class MyDbContext : DbContext { public MyDbContext() { } }

回答16:

Worked for me:

 UnInstall-Package EntityFramework 

• Restart Visual Studio

Install-Package EntityFramework

• Build project