How to run EF Core commands when your entities are in a different project from your dbcontext?

Time needed: 15 minutes

How to run EF Core commands for a different project?

1. Prerequisites

   You have configured your project somewhat like this:
   
   .sln root:
   – Contoso.DbAccess (contains your dbcontext(s)
   – Contoso.Entities (contains your entities)
   – Contoso.App (web app or desktop or whatever)
   
   In my case, I had a couple of console applications and 2 Azure IoT Edge modules using the same entities, but only one of them needed the database context, hence the configuration.

2. Select the right working directory

   No matter where you run the commands from, this seems to be the best option – don’t use –project, rather cd to the directory that your DbContext project is in. I don’t know why, but it seems to work more stable for me this way.
   
   Otherwise, you might get this error:
   
   Unable to retrieve project metadata. Ensure it's an SDK-style project. If you're using a custom BaseIntermediateOutputPath or MSBuildProjectExtensionsPath values, Use the --msbuildprojectextensionspath option.
   
   Or:
   
   No project was found. Change the current working directory or use the --project option.
   
   So figure out which folder the project that you define your DbContext class(es) is in, and change that to be your working directory.
   
3. Configure your startup project

   With dotnet cli, you’ll need to add an executable project as the startup project by adding “–startup-project” and either the absolute or relative URI to your executable project’s .csproj-file.
   
   dotnet ef migrations add NewMigration --startup-project "../Contoso.App/MyWebAppProject.csproj"
   
   Remember that “../”! It’ll traverse one step up and then refer to your other project, in this case, a web app project. Or just use an absolute path instead.
   
   This project can be any project that has .AddDbContext() or var db = new DbContext() -call in it. I have had the most consistent results with web projects, but that’s probably just a coincidence 🧐
   
   With EF Core PowerShell commandlets, you should select the startup project from Solution Explorer.

4. Make sure your startup project has your database context configured

   Ah, this is pretty darn important. The project to which you’re referring with your –startup-project needs to have the database context configured one way or another.
   
   One way to do this (for an ASP.NET Core web application with PostgreSQL database) would be shown below:
   
   services.AddDbContext(
options =>
options.UseNpgsql("Host=DBHost;Port=5432;Database=MyDB;Username=user;Password=pass",
x => x.MigrationsAssembly("MyDbContext")));
   
   Make note of the “x.MigrationsAssembly()” ! That part should reference the name of the assembly that actually has your DbContext and the code-first Migrations defined.