add-migration throws error File web.dll not found. The startup project is where DbContext is. Web is the asp.net core project

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add-migration throws error File web.dll not found. The startup project is where DbContext is. Web is the asp.net core project

Pablo The Tiger 186

Greetings, Ladies and Guys!

So finally I found a tutorial of Razor Pages C#, with jQuery AJAX.

The solution has 3 projects: Web (asp.net core razor pages app, here goes the config, such as connection string and some services), Core (Model and Interfaces), and Infrastructure (here goes the DbContext and Repositories).

So I tried to run: add-migration Initial

and the output was:

Build started

Builder succeeded

File 'C:\Users\PABLO\source\repos\RazorCRUD.jQueryAJAX\Infrastructure\bin\Debug\net9.0\Web.dll' not found.

In the Package Manager Console (where I write the before) in the dropdown it is selected the project Infrastructure (where is DbContext)

If I run: update-database it occurs the same messages.

I searched a lot and saw something like:

Add-Migration InitialCreate -Project Web -StartupProject Infrastructure

but it doesn't work

Your help is much appreciated

Pablo

Answer accepted by question author

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Answer 1

Jack Dang (WICLOUD CORPORATION) 14,955 Microsoft External Staff Moderator

Hi @Pablo The Tiger ,

Thanks for reaching out.

The issue you’re seeing happens because EF Core needs both the project where your DbContext lives and the project that contains your app configuration. In your solution:

Infrastructure -> contains DbContext
Web -> contains connection string and services

If EF Core tries to use Infrastructure as the Startup Project, it can’t find Web.dll, which causes the error.

Try running this instead:

Add-Migration InitialCreate -Project Infrastructure -StartupProject Web

This tells EF Core:

DbContext is in Infrastructure
Startup Project is Web (so it can read the connection string)

Then run:

Update-Database -Project Infrastructure -StartupProject Web

Hope this helps! If my answer was helpful - kindly follow the instructions here so others with the same problem can benefit as well.

Pablo The Tiger 186 Reputation points

2026-02-26T14:04:45.6+00:00

Hello, @Jack Dang (WICLOUD CORPORATION)

Thanks for your answer.

Here I show you the output with the command you gave me.

I have already tested inverting the projects and every way gives a different error.

I tried also in the Power Shell instead of the Package Manager Console, and this is the output:

PS C:\Users\PABLO\source\repos\RazorCRUD.jQueryAJAX\Infrastructure> Add-Migration InitialCreate -Project Infrastructure -StartupProject Web Add-Migration : El término 'Add-Migration' no se reconoce como nombre de un cmdlet, función, archivo de script o programa ejecutable. Compruebe si escribió correctamente el nombre o, si incluyó una ruta de acceso, compruebe que dicha ruta es correcta e inténtelo de nuevo. En línea: 1 Carácter: 1 + Add-Migration InitialCreate -Project Infrastructure -StartupProject W ... + ~~~~~~~~~~~~~ + CategoryInfo : ObjectNotFound: (Add-Migration:String) [], CommandNotFoundException + FullyQualifiedErrorId : CommandNotFoundException

I don't know what to do. The answer that everyone (Internet, you, the AI) gives me doesn't work, it seems it takes as startup project the one that has DbContext, but if I invert the projects, it throws the error of File web.dll not found.

Surely I'm doing something wrong

Thank you
Pablo The Tiger 186 Reputation points

2026-02-27T01:30:32.2466667+00:00

Dear @Jack Dang (WICLOUD CORPORATION)

Could it be the problem the location of the Nuget Packages? Should they be located in the Infrastructure or in the Web project? Or in both? You saw the error message, it says "Your startup project Web doesn't reference EF Core .... . I have all the Packages in the Infrastructure project, cos that way is in the tutorial.

Or if it is not the before, if you could "guess" what it is, you that you are a Senior developer obviously, I would be very grateful to you.

Thank you

Pablo
Jack Dang (WICLOUD CORPORATION) 14,955 Reputation points Microsoft External Staff Moderator

2026-02-27T08:58:43.89+00:00
Hi @Pablo The Tiger ,

Thanks for your follow-up.

The key error you’re seeing:

Your startup project 'Web' doesn't reference Microsoft.EntityFrameworkCore.Design

This isn’t about where NuGet packages are stored. It simply means the Web project (your startup project) is missing the EF Core design-time package required for migrations to run.

Since all your EF packages are currently only in Infrastructure, that explains why the command fails. Runtime packages can stay in Infrastructure, but the startup project (Web) must also reference:

Microsoft.EntityFrameworkCore.Design

Even though your DbContext lives in Infrastructure.

Here’s what to do next:

Right-click the Web project -> Manage NuGet Packages

Install:

Microsoft.EntityFrameworkCore.Design

Then in Package Manager Console, run:

Add-Migration InitialCreate -Project Infrastructure -StartupProject Web Update-Database -Project Infrastructure -StartupProject Web

No need to invert projects or move existing EF runtime packages.

About the PowerShell error:

Add-Migration : The term 'Add-Migration' is not recognized

Add-Migration only works inside Visual Studio’s Package Manager Console. If you want to use normal PowerShell, use:

dotnet ef migrations add InitialCreate --project Infrastructure --startup-project Web

Just make sure:

The dotnet-ef tool is installed globally (dotnet tool install --global dotnet-ef)

Microsoft.EntityFrameworkCore.Design is referenced in Web

At this stage, the missing Design package in Web is the blocking issue.

Please try that and let me know how it goes.
Pablo The Tiger 186 Reputation points

2026-03-02T05:52:07.7566667+00:00

Now it's everything fine. Thank you very much, @Jack Dang (WICLOUD CORPORATION) . Your help is really appreciated.
Jack Dang (WICLOUD CORPORATION) 14,955 Reputation points Microsoft External Staff Moderator

2026-03-02T06:08:34.66+00:00

Hi @Pablo The Tiger ,

Thanks for your kind feedback.

If you have new questions in the future, feel free to post them on this platform and I'm happy to support.

Answer 2

It seems like you are encountering an issue with the add-migration command in your ASP.NET Core project setup. The error message indicates that the Web.dll file cannot be found, which typically means that the command is not able to locate the startup project correctly.

Here are some steps you can take to resolve this issue:

Check Project Configuration: Ensure that the Web project is set as the startup project in Visual Studio. You can do this by right-clicking on the Web project in Solution Explorer and selecting "Set as Startup Project."
Use Correct Command: When running the migration command, make sure you specify the correct parameters. Since your DbContext is in the Infrastructure project and your startup project is Web, you should run:
```
   Add-Migration InitialCreate -Project Infrastructure -StartupProject Web
```
This tells the command to look for the DbContext in the Infrastructure project while using the Web project as the startup.
Build the Solution: Before running the migration command, ensure that the solution builds successfully. You can do this by selecting "Build Solution" from the Build menu in Visual Studio.
Check Output Path: Verify that the output path for the Web project is correctly set. You can check this in the project properties under the "Build" tab. Ensure that the output path matches where the Web.dll should be generated.
Clean and Rebuild: Sometimes, cleaning the solution and then rebuilding it can resolve issues with missing files. You can do this by selecting "Clean Solution" followed by "Rebuild Solution" from the Build menu.

If you follow these steps and still encounter issues, consider checking the project dependencies and ensuring that all necessary packages are installed and up to date.

References:

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add-migration throws error File web.dll not found. The startup project is where DbContext is. Web is the asp.net core project

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