Could not load assembly... Ensure it is referenced by the startup project

I encountered such a problem. After hours of fixing it, I found that the problem is the Package Manager Console or Visual Studio CLI.

I used Windows Command Prompt and dotnet tool

> dotnet ef migrations add migration_name

After executing the command, it successes without any error with the message:

> Done. To undo this action, use 'ef migrations remove

Could not load assembly 'Data'. Ensure it is referenced by the startup project 'TheFarmersMarketApp'.

Please make sure that you add the Data assembly into the project TheFarmersMarketApp. Please make sure that all projects that need to reference this project have a direct reference to it, as long as it does not cause a circular dependency or other issues.

First of all you need to select a proper project in your Nuget Package Manager Console. As you can see on your first screen the default project is TheFarmersMarketApp, but it is not right. You need to select the Data project, because your migrations must lay near your context class.

Then you should use a short version of your command:

Add-Migration "Initial Migration" 

Had this issue due to switching my project's target to x86 in order for it to run with an older library.

My Fix: Right click on your project then select Properties - Build - General - and set platform Target to x64, run your command then switch back to x86 if necessary for your project to run.