belongs_to with :class_name option fails
class User < ActiveRecord::Base has_many :books, :foreign_key => 'author_id'endclass Book < ActiveRecord::Base belongs_to :author, :class_name => 'User', :foreign_key => 'author_id', :validate => trueendThe best thing to do is to change your migration and change author_id to user_id. Then you can remove the :foreign_key option.
It should be
belongs_to :user, :foreign_key => 'author_id'if your foreign key is author id. Since you actually have User class, your Book must belong_to :user.
migration
t.belongs_to :author, foreign_key: { to_table: :users }working on rails 5