Does EF Core allow a unique column to contain multiple nulls?

Question

My entity has a property which is allowed to be null. BUT, if it isn\'t null, then it must be unique. In other words, the column is unique but allows multiple nulls.

Answer 1

Yes, you can do that with EF Core, as a Unique index by default is created as a filtered index (WHERE ... IS NOT NULL)

config.Entity<Product>()
        .HasIndex(b => b.ProductId)
        .IsUnique();

https://github.com/aspnet/EntityFramework/pull/2868