rails has many through where query - sql

Question

My model structure is set up like this,
class Conversation < ActiveRecord::Base
has_many :conversation_statuses, :dependent => :destroy
has_many :users, :through => :conversation_statuses
has_many :messages, :inverse_of => :conversation
accepts_nested_attributes_for :messages
end
class User < ActiveRecord::Base
has_many :conversation_statuses, :dependent => :destroy
has_many :conversations, :through => :conversation_statuses
has_many :messages, :inverse_of => :user
end
class ConversationStatus < ActiveRecord::Base
belongs_to :user
belongs_to :conversation
end
I am trying to create a conversation only if the users don't have a conversation going. I have conversation set up so that more than 2 users can have a conversation. Right now my query is finding conversations including the user ids, but that may include conversations with large groups. My controller query looks like this,
class ConversationsController < ApplicationController
before_filter :set_user_ids_param, :only => :create
def create
#conversation = Conversation.joins(:users)
.where(:users => {:id => params[:conversation][:user_ids]})
.first_or_initialize
#conversation.attributes = conversation_params
if #conversation.save
render :json => { :html => render_new_conversation_form }
return
end
render :status => :bad_request, :json => {
:html => render_conversation_form
}
end
private
def conversation_params
params.require(:conversation).permit([
:user_ids => [],
:messages_attributes => [
:content,
:topic
]
])
end
def set_user_ids_param
return if params[:conversation].blank?
return if params[:conversation].blank? || params[:conversation][:user_ids].blank?
params[:conversation][:user_ids] = params[:conversation][:user_ids].split(',')
params[:conversation][:user_ids].push(current_user.id)
end
def render_new_conversation_form
render_to_string({
:partial => 'conversations/form',
:locals => {
:conversation => #conversation
}
})
end
def render_conversation_form
render_to_string({
:partial => 'conversations/form',
:locals => {
:conversation => #conversation
}
})
end
end
and my form looks like this
= simple_form_for conversation, :html => {:class => 'conversation-form'} do |form|
= form.input :user_ids, :as => :hidden, :input_html => {:class => 'user-ids'}
= form.simple_fields_for :messages do |message_fields|
= render 'messages/fields', :message_fields => message_fields
%button.button.radius.submit.no-margin
Send Message
%button.button.secondary.radius.cancel.no-margin
Cancel
Any ideas on the best way to handle this?

Answer 1

The method that will resolve your problem should be in class ConversationStatus, which will give you the conversation_id of the Conversation, if it exists.
You'll need two sets:
containing_all_users are the conversations that contain all the users in users_id
with_extra_users are the conversations that have more users than those in users_id
The conversation (if exists), is the result of the subtraction of those sets.
class ConversationStatus < ActiveRecord::Base
belongs_to :user
belongs_to :conversation
def self.find_between(user_ids)
containing_all_users = group(:conversation_id)
.where(user_id: user_ids)
.having(['COUNT(user_id) = ?', user_ids.length])
.pluck(:conversation_id)
with_extra_users = group(:conversation_id)
.having(['COUNT(user_id) > ?', user_ids.length])
.pluck(:conversation_id)
(containing_all_users - with_extra_users).first
end
end
You'll get the conversation from the Conversation model. You should set the attributes on this method too:
class Conversation < ActiveRecord::Base
has_many :conversation_statuses, dependent: :destroy
has_many :users, through: :conversation_statuses
def self.find_between(user_ids, attributes = {})
conversation_id = ConversationStatus.find_between(user_ids)
Conversation.where(id: conversation_id).first_or_initialize(attributes)
end
end
On the controller you will call it like this:
#conversation = Conversation.find_between(params[:conversation][:user_ids],
conversation_params)