Entity framework performance issue, saveChanges is very slow

Turn off change tracking before you perform your inserts. This will improve your performance significantly (magnitudes of order). Putting SaveChanges() outside your loop will help as well, but turning off change tracking will help even more.

using (var context = new CustomerContext())
{
    context.Configuration.AutoDetectChangesEnabled = false;

    // A loop to add all your new entities

    context.SaveChanges();
}

See this page for some more information.

I would take the SaveChanges(book) outside of the foreach. Since book is on the entity as a list, you can put this outside and EF will work better with the resulting code.

The list is an attribute on the entity, and EF is designed to optimize updates/creates/deletes on the back end database. If you do this, I'd be curious whether it helps.