Entity Framework 6 Code First: error 3023: Problem in mapping fragments starting at lines xxxx:Column has no default value and is not nullable. A column value is required to store entity data

There are many reasons why this error would happen. There's a known bug in 6.1 which will be fixed in 6.2. But my problem wasn't related to it. Here's what happened for me.

I use a single table, tbl_Person,  to map a hierarchy, like this example, where Person is abstract :

And I use this mapping using Fluent API:

modelBuilder.Entity<Person>()
 .ToTable("tbl_Person")
 .HasKey(m => m.PersonID)
 .Map<Student =>(m.Requires (discrimination stuff) )
 .Map<Instructor>(m => m.Requires (discrimination stuff) )

And then later, I added another kind of Person to my model. Let's say a "Director"  but I forgot to add the mapping. That got me the error whenever I would try to use a DbContext. So I just added the mapping for "Director" and the error went away.

By the way, a discriminator column can be NOT NULL and have no default value, as opposed to what the error lead me to think.

Coffee time!