Turns out this could also be caused by BuildEvents. For me I was referencing $(SolutionDir) there. With a regular build this variable has value, but running dotnet * commands is done at project level apparently. $(SolutionDir) comes out like Undefined in verbose mode (-v). This seems like a bug to me.

1: I was getting the error: PM> Add-Migration "InitialDB" Build failed. 2:The error was the "(" missing. I corrected that and error is gone.

so the error you can see the error in the output. The error was because of the code issue.

Got the same error when I tried to run add-migration. Make sure that you don't have any syntax errors in your code.

I had a syntax error in my code, and after I fixed it, I was able to run add-migration.

The developer ended up un-mapping the project from TFS, deleting it, and re-mapping it. It's now working for him.

I had exact same error but I am using Visual Studio Community 2017 Version 15.2 (26430.14) to build .Net Core projects.

I have a ASP.NET Core MVC web project and a separate security project using ASP.NET Core Identity. The web project contains connection string in aspsettings.json config file.

I also installed Bundler & Minifier and Web Essentials 2017 extensions in Visual Studio so that I can compile, minify and bundle my assets and put them to wwwroot.

I figured out it was the MSBuild those 2 extensions secretly download that caused the problem, because I had Enable Bundle on Build and Enable Compile on Build on. After I disable that, everything works fine.

Probably not the cause to your problem, but might be worthy to just give it a try.

I had the exact same problem (.NET Core 2.0.1).

Sometimes it helps if the project is rebuilt.

I also encounter the problem when I opened the project in 2 Visual Studios.
Closing one Visual Studio fixed the error.

Had the same situation. This helped:

1. Open Package Manager Console

2. Change directory to Migrations folder:

   cd C:\YourSolution\YourProjectWithMigrations
   

3. Enter in PM:

   dotnet ef migrations add YourMigrationName
   

It's because of other projects in your solutions. e.g If you have two projects in your solution as Project A and Project B. If Project A is not successful build and then Project B data migration will fail. So you should unload Project A and add the migration to Project B again.

I think this is not a good answer but hope this help.

I think this happened to me when I tried to run dotnet ef migrations add xyz whilst it was already running.

In the end, just to be sure, I stopped the currently running instance, then ran it again to ensure it was rebuilt, stopped it again and I was able to run the dotnet ef migrations add command

In my situation it was the error

namespace aspnetcore does not exist .. are you missing a reference?

I have figured it out by adding the -v (or --verbose) flag to the dotnet ef command.

Open Output window in Visual Studio and check your build log. In my case, even though my current configuration was Release, Add-Migration built the project in Debug, which had an error. For some reason, VS didn't display the error anywhere except Output window for me.

I think the 2 commands below always work (if you run them at project's folder)

• dotnet ef migrations add (database object fron ApplicationDbContextDBContext)
• dotnet ef database update

maybe it cause because of you did not add this in YOUR_PROJECT.csproj

<ItemGroup>

<DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.Dotnet" Version="2.0.2" />

Most likely that there is an existing error in your code. Try rebuilding first and correct all the errors.

Happened to me, I am trying to rollback migration but I have not corrected the errors in the code yet.

I had the same error. What I did, I corrected the error the one I have in code, and rebuilt the project. Then I ran the ms-dos command and it worked.

Try saving DataContext.cs first. It worked for me.

Try these steps:

1. Clean the solution.

2. Build every project separately.

3. Resolve any errors if found (sometimes, VS is not showing errors until you build it separately).

4. Then try to run migration again.

I suggest adding -v to have more info.

In my example, I had to add <LangVersion>latest</LangVersion> to my projects, as this was missing from some of them.

Just got into this issue. In my case, I was debugging my code and it was making my migrations fail.

Since in Visual Studio Code, the debugger is so low-profile (only a small bar), I didn't realize about this until I read some questions and decided to look better.

In my case, the application was running. Apparently, it needs to be stopped. Weird error message anyways.

Make sure you have code generation inside startup.cs

Example

<Project Sdk="Microsoft.NET.Sdk.Web">

<PropertyGroup>
<TargetFramework>netcoreapp2.1</TargetFramework>
</PropertyGroup>

<ItemGroup>
<PackageReference Include="Microsoft.AspNetCore.App" />
 <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="2.1.2" />
<PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="2.1.3" />
 </ItemGroup>

</Project>

I got the same error. I fixed it by stopping the project build. After that it worked fine.

I got the same error. There were no errors during the build proccess. I closed the Visual Studio and it worked.

In my case it was failing because an unrelated project in the solution was failing. Unloading that project and running the command again worked.

In my case it was because i had error somewhere.. Like missing coma in db config file, so VS didn't throw exception until build

So just try to run your code...

I had the same problem when running: dotnet ef migrations add InitialCreate so what I did is tried to build the project using: dotnet build command.

It throws an error : Startup.cs(20,27): error CS0103: bla bla for example. which you can trace to find the error in your code.

Then i refactored the code and ran: dotnet build again to check any errors until there is no errors and build is succeded. Then ran: dotnet ef migrations add InitialCreate then the build succeded.

I was struggling with this one while using Visual Studio 2019 version 16.5.0.

What solved it finally:

• Close Visual Studio;
• Reopen Visual Studio;
• Make sure you right click the Solution if you have multiple projects and select Rebuild Solution.

Note that I tried doing a Rebuild Solution before and that did not catch the error. So it's important to close VS and reopen it.

It then showed the error that was causing add-migration command to fail with Build failed message.

this is because deleting projects or class libraries from solution and adding projects after deleting with same name. best thing is delete solution file and add projects to it.this works for me (I did this using vsCode)

Same errors for me. I tried -v but nothing. Then I realised I had changed the model so much that the controller was showing errors.

Once I fixed the errors in the controller it worked.

It might have many possibilities I guess. In my case, it was due packages versions inbalance

I had

<PackageReference Include="Microsoft.EntityFrameworkCore" Version="3.1.1"/>
<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.1.3"/>

I just need it to downgrade the core Design package to 3.1.1 to match the upper core version

<PackageReference Include="Microsoft.EntityFrameworkCore" Version="3.1.1"/>
<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="3.1.1"/>

Then it worked fine

In My case, add the package Microsoft.EntityFrameworkCore.Tools fixed problem

In my case I had couple of such errors:

The process cannot access the file 'C:\xxx\bin\Debug\netcoreapp3.1\yyy.dll' 
because it is being used by another process. [C:\zzz.csproj]

I was able to see those errors only after adding -v parameter.

The solution was to shutdown the Visual Studio and run the command again.

In my case rebuilding the Project worked fine. Running the project worked fine too and executing some endpoints worked.

But still on update-database it would say "Build Failed" without any clarification, even with -Verbose added to the command.

At the end it happened that there was an error in Unit Test project that would (for some reason) cause "Build Failed" error.

Since I have multiple projects under the same Solution, I would just rebuild the Project that I am currently working on. It appears that when this error happens that it would be better to rebuild whole Solution and resolve errors...

Only clearing Visual Studio cache helped me

1. Close Visual Studio (ensure devenv.exe is not present in the Task Manager)
2. Delete the %USERPROFILE%\AppData\Local\Microsoft\VisualStudio\16.0\ComponentModelCache directory.
3. Restart Visual Studio. You could also need to cleanup your user's temp folder. It is usually located under %USERPROFILE%\AppData\Local\Temp.

I had the same problem. If you have opted .NET Core tool collect usage data for Windows improvement then you can use dotnet build to get the missing/persisting problem.

In my case it was sonarqube dependencies that were missing. When I built the project in Rider it succeeded but failed when triggered the build (dotnet build) from terminal. This was caused by a incorrect setup in Rider. The solution was to trigger a sonar scan in terminal.