Hot to Fix The exception 'GenericArguments[0], 'PizzaStore.PizzaDb', on 'Microsoft.EntityFrameworkCore.Design.IDesignTimeDbContextFactory`1[TContext]' violates the constraint of type 'TContext'.' was thrown while attempting to find 'DbContext' types.

Question

I'm studing the module 'Exercise - Use the SQLite database provider with EF Core' (https://learn.microsoft.com/en-us/training/modules/build-web-api-minimal-database/5-exercise-use-sqlite-database), but when I try to set up the SQLite database to my application, I receite the following error:

The exception 'GenericArguments[0], 'PizzaStore.PizzaDb', on 'Microsoft.EntityFrameworkCore.Design.IDesignTimeDbContextFactory`1[TContext]' violates the constraint of type 'TContext'.' was thrown while attempting to find 'DbContext' types. For the different patterns supported at design time, see https://go.microsoft.com/fwlink/?linkid=851728

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Answer 1

Hi Raphael Soares,

Thank you for reaching out to Microsoft Q & A forum.

I've completed the tutorial exercise on Use a database with minimal API, Entity Framework Core, and ASP.NET Core module, and I found the instructions straightforward and easy to follow. 

Regarding the issue you're experiencing, it appears to stem from a mismatch between the specified DbContext type and the expected type. This mismatch is resulting in an exception during the design-time discovery of DbContext. 

To help resolve this, I suggest the following steps: 

1.Ensure Correct DbContext Implementation: Confirm that your DbContext implementation (in this case, PizzaDb) properly inherits from the DbContext class. This is essential for Entity Framework Core to recognize it as a valid context. 

2.Check Design-Time Configuration: Verify that your design-time configuration is accurately set up. Ensure that your DbContext includes a public constructor with the necessary parameters and that it's correctly registered for design-time services. 

3.Verify Dependencies: Double-check that all dependencies and packages required for Entity Framework Core are correctly installed and up to date. Sometimes, issues like mismatched versions or missing dependencies can lead to such exceptions. 

4.Review Code for Errors: Thoroughly inspect your code for potential errors, such as typos or incorrect type declarations, particularly within your DbContext class and its associated configurations. 

By carefully examining and addressing these areas, you should be able to troubleshoot and resolve the issue effectively. 

If you encounter any future issues, please feel free to contact us, and we will be pleased to assist you further.   

If you have found the answer provided to be helpful, please click on the "Accept answer/Upvote" button so that it is useful for other members in the Microsoft Q&A community.  

Thank you.