model: add members_by_recent_rsvp method to Group

Adds a class method that returns group members sorted by their most
recent workshop RSVP (most recent first, members with no RSVP at end).
Includes test coverage for the new method.

Author: mroderick

app/models/group.rb

@@ -11,6 +11,15 @@ class Group < ApplicationRecord
   scope :students, -> { where(name: 'Students') }
   scope :coaches, -> { where(name: 'Coaches') }
 
+  def self.members_by_recent_rsvp(group)
+    group.members
+         .joins('LEFT JOIN workshop_invitations ON workshop_invitations.member_id = members.id')
+         .joins('LEFT JOIN workshops ON workshops.id = workshop_invitations.workshop_id')
+         .select('members.*, MAX(workshops.date_and_time) as last_rsvp_at')
+         .group('members.id')
+         .order('MAX(workshops.date_and_time) DESC NULLS LAST')
+  end
+
   validates :name, presence: true, inclusion: { in: NAMES, message: 'Invalid name for Group' }
 
   alias city chapter

spec/models/group_spec.rb

@@ -27,4 +27,26 @@
       expect(group.eligible_members).to be_empty
     end
   end
+
+  describe '.members_by_recent_rsvp' do
+    let(:group) { Fabricate(:group, name: 'Students') }
+    let(:chapter) { group.chapter }
+
+    it 'orders members by most recent workshop RSVP' do
+      old_workshop = Fabricate(:workshop, chapter: chapter, date_and_time: 1.month.ago)
+      new_workshop = Fabricate(:workshop, chapter: chapter, date_and_time: 1.week.ago)
+
+      member_old = Fabricate(:member, groups: [group])
+      member_new = Fabricate(:member, groups: [group])
+      _member_no_rsvp = Fabricate(:member, groups: [group])
+
+      Fabricate(:workshop_invitation, workshop: old_workshop, member: member_old, attending: true)
+      Fabricate(:workshop_invitation, workshop: new_workshop, member: member_new, attending: true)
+
+      results = Group.members_by_recent_rsvp(group).to_a
+
+      expect(results.first).to eq(member_new)
+      expect(results.last).to eq(_member_no_rsvp)
+    end
+  end
 end