EntityFramework context across multiple projects or joining between two contexts
c# entity-framework entity-framework-core
Question
I have a class library project containing an EF Core db context. This is part of a framework.
I want to extend this context but without making changes to the framework project. The second context would use the same database.
I created another db context in a different class library (something similar to this). This works ok, I can make queries and create migrations separately from the other context.
But for example if I have a User entity in the first context and UserBooks in the second, when I try to make a join between the two contexts it doesn't work, getting exception
System.ArgumentNullException: Value cannot be null. Parameter name: entityType
This is a known issue.
Also tried with latest NuGet package 3.0.0-preview3.19153.1 but the only difference is that the error message is better
Cannot use multiple DbContext instances within a single query execution. Ensure the query uses a single context instance
Is there any way to
a. make joins between two contexts
or
b. extend a context in a separate project without making any (or minimal) changes to the 'main' context
Popular Answer
You could make your second context inherit the first.
public class MyFirstContext : DbContext
{
public DbSet<User> Users { get; set; }
}
public class MySecondContext : MyFirstContext
{
public DbSet<UserBook> UserBooks { get; set; }
}
Of course, your second context could be in a different assembly. Now you only need MySecondContext in your application. You will be able to join Users and UserBooks.
Related Questions
Licensed under: CC-BY-SA with attribution
Not affiliated with Stack Overflow