I\'ve been trying to create navigation properties for my collection types and I found this example of how one person accomplished it using OnModelCreating. I gave it a try i
I know this is a late response, and this may only work for people working off tutorials or school projects!
For me, just deleting the database, .mdf, and migrations folder fixed it. Now, I don't know if you are using migrations, but this worked for me.
I'm a novice, but what I've noticed is that Identity is very finicky with keys. Deleting the migration has helped with every (godforsaken) migration problem I've hit with my project.