ActiveRecord::AssociationTypeMismatch

Raised when an object assigned to an association has an incorrect type.

  class Ticket < ActiveRecord::Base
    has_many :patches
  end

  class Patch < ActiveRecord::Base
    belongs_to :ticket
  end

  # Comments are not patches, this assignment raises AssociationTypeMismatch.
  @ticket.patches << Comment.new(:content => "Please attach tests to your patch.")