fix: add unique index on subscriptions to prevent duplicate entries

app/models/invitation_manager.rb

@@ -62,10 +62,10 @@ def log_event_meeting_invitation_failure(context, member, error)
   end
 
   def chapter_students(chapter)
-    Member.in_group(chapter.groups.students)
+    Member.in_group(chapter.groups.students).distinct
   end
 
   def chapter_coaches(chapter)
-    Member.in_group(chapter.groups.coaches)
+    Member.in_group(chapter.groups.coaches).distinct
   end
 end

db/migrate/20260408220120_fix_duplicate_subscriptions_and_add_unique_index.rb

@@ -0,0 +1,30 @@
+class FixDuplicateSubscriptionsAndAddUniqueIndex < ActiveRecord::Migration[8.1]
+  disable_ddl_transaction!
+
+  def up
+    execute <<~SQL
+      DELETE FROM subscriptions
+      WHERE id NOT IN (
+        SELECT MIN(id)
+        FROM subscriptions
+        GROUP BY member_id, group_id
+      )
+      AND (member_id, group_id) IN (
+        SELECT member_id, group_id
+        FROM subscriptions
+        GROUP BY member_id, group_id
+        HAVING COUNT(*) > 1
+      )
+    SQL
+
+    add_index :subscriptions,
+              %i[member_id group_id],
+              unique: true,
+              name: 'index_subscriptions_on_member_id_group_id',
+              algorithm: :concurrently
+  end
+
+  def down
+    remove_index :subscriptions, name: 'index_subscriptions_on_member_id_group_id'
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.1].define(version: 2026_03_30_193245) do
+ActiveRecord::Schema[8.1].define(version: 2026_04_08_220120) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_catalog.plpgsql"
 
@@ -525,6 +525,7 @@
     t.integer "member_id"
     t.datetime "updated_at", precision: nil
     t.index ["group_id"], name: "index_subscriptions_on_group_id"
+    t.index ["member_id", "group_id"], name: "index_subscriptions_on_member_id_group_id", unique: true
     t.index ["member_id"], name: "index_subscriptions_on_member_id"
   end
 

spec/models/invitation_manager_deduplication_spec.rb

@@ -0,0 +1,69 @@
+require 'rails_helper'
+
+RSpec.describe InvitationManager do
+  subject(:manager) { InvitationManager.new }
+
+  let(:chapter) { Fabricate(:chapter) }
+  let(:member_in_both_groups) { Fabricate(:member, accepted_toc_at: Time.zone.now) }
+
+  describe '#chapter_students' do
+    context 'when a member has multiple subscriptions to the same group type' do
+      before do
+        students_group1 = Fabricate(:group, name: 'Students', chapter: chapter)
+        students_group2 = Fabricate(:group, name: 'Students', chapter: chapter)
+        students_group1.members << member_in_both_groups
+        students_group2.members << member_in_both_groups
+      end
+
+      it 'returns unique members' do
+        result = manager.send(:chapter_students, chapter)
+
+        expect(result.count).to eq(1)
+        expect(result).to contain_exactly(member_in_both_groups)
+      end
+    end
+  end
+
+  describe '#chapter_coaches' do
+    context 'when a member has multiple subscriptions to the same group type' do
+      before do
+        coaches_group1 = Fabricate(:group, name: 'Coaches', chapter: chapter)
+        coaches_group2 = Fabricate(:group, name: 'Coaches', chapter: chapter)
+        coaches_group1.members << member_in_both_groups
+        coaches_group2.members << member_in_both_groups
+      end
+
+      it 'returns unique members' do
+        result = manager.send(:chapter_coaches, chapter)
+
+        expect(result.count).to eq(1)
+        expect(result).to contain_exactly(member_in_both_groups)
+      end
+    end
+  end
+
+  describe 'sending invitations to members in both students and coaches groups' do
+    let(:workshop) { Fabricate(:workshop, chapter: chapter) }
+    let(:students_group) { Fabricate(:group, name: 'Students', chapter: chapter) }
+    let(:coaches_group) { Fabricate(:group, name: 'Coaches', chapter: chapter) }
+
+    before do
+      students_group.members << member_in_both_groups
+      coaches_group.members << member_in_both_groups
+    end
+
+    it 'sends one invitation per role when audience is everyone' do
+      expect(WorkshopInvitation).to receive(:find_or_create_by)
+        .with(workshop: workshop, member: member_in_both_groups, role: 'Student')
+        .and_call_original
+        .once
+
+      expect(WorkshopInvitation).to receive(:find_or_create_by)
+        .with(workshop: workshop, member: member_in_both_groups, role: 'Coach')
+        .and_call_original
+        .once
+
+      manager.send_workshop_emails(workshop, 'everyone')
+    end
+  end
+end