如何通过多个其他表检索关联记录？

Question

Here's a simple setup where the user will always be a patient, and the user may or may not also be a physician:

# user.rb
  has_one :physician
  has_one :patient

# physician.rb
  belongs_to :user
  validates_uniqueness_of :user_id
  has_many :appointments
  has_many :patients, :through => :appointments

# patient.rb
  belongs_to :user
  validates_uniqueness_of :user_id 
  has_many :appointments
  has_many :physicians, :through => :appointments

It all connects to appointments and then to conversations, like so:

# appointment.rb
  belongs_to :physician
  belongs_to :patient
  has_one :conversation
  has_many :messages, through: :conversation

# conversation.rb
  belongs_to :appointment
  belongs_to :sender, foreign_key: :sender_id, class_name: "User"
  belongs_to :recipient, foreign_key: :recipient_id, class_name: "User"
  has_many :messages

Sometimes I really want to be able to do this:

current_user.conversations

but that doesn't work, and instead I would have to do something like this:

current_user.physician.appointment.includes(:conversation)
# somehow combine results with this
current_user.patient.appointment.includes(:conversation)

Question

What do I need to do (and where) so that I can call current_user.conversations and it will retrieve all the conversations (ie those as a patient, and those as a physician (noting the user may or may not be a physician).

Note: open to suggestion if what I'm suggesting isn't good practice.

Answer 1

Based on your current design, in the User model, you can simply add a method for conversations :

def conversations
  Conversation.where(sender: self).or(Conversation.where(recipient: self))
end

I am not sure why a conversation would have a sender and recipient as a user can be both a sender (of a message) and recipient (of a message) in a conversation. I would drop the sender_id and recipient_id from the conversations table and just match the conversations based on appointments .

def conversations
  Conversation
   .joins(appointment: [:physician, :patient])
   .where('physicians.user_id = :user_id or patients.user_id = :user_id', user_id: id)
end