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backend/migrations/20251112-add-performance-indexes.js

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+/**
+ * Migration: Add Database Indexes for Performance Optimization
+ * 
+ * This migration adds indexes to improve query performance for:
+ * - QuizSession: userId, guestSessionId, categoryId, status, createdAt
+ * - QuizSessionQuestion: quizSessionId, questionId
+ * 
+ * Note: Other models (User, Question, Category, GuestSession, QuizAnswer, UserBookmark) 
+ * already have indexes defined in their models.
+ */
+
+module.exports = {
+  up: async (queryInterface, Sequelize) => {
+    console.log('Adding performance indexes...');
+    
+    try {
+      // QuizSession indexes
+      await queryInterface.addIndex('quiz_sessions', ['user_id'], {
+        name: 'idx_quiz_sessions_user_id'
+      });
+      
+      await queryInterface.addIndex('quiz_sessions', ['guest_session_id'], {
+        name: 'idx_quiz_sessions_guest_session_id'
+      });
+      
+      await queryInterface.addIndex('quiz_sessions', ['category_id'], {
+        name: 'idx_quiz_sessions_category_id'
+      });
+      
+      await queryInterface.addIndex('quiz_sessions', ['status'], {
+        name: 'idx_quiz_sessions_status'
+      });
+      
+      await queryInterface.addIndex('quiz_sessions', ['created_at'], {
+        name: 'idx_quiz_sessions_created_at'
+      });
+      
+      // Composite indexes for common queries
+      await queryInterface.addIndex('quiz_sessions', ['user_id', 'created_at'], {
+        name: 'idx_quiz_sessions_user_created'
+      });
+      
+      await queryInterface.addIndex('quiz_sessions', ['guest_session_id', 'created_at'], {
+        name: 'idx_quiz_sessions_guest_created'
+      });
+      
+      await queryInterface.addIndex('quiz_sessions', ['category_id', 'status'], {
+        name: 'idx_quiz_sessions_category_status'
+      });
+      
+      // QuizSessionQuestion indexes
+      await queryInterface.addIndex('quiz_session_questions', ['quiz_session_id'], {
+        name: 'idx_quiz_session_questions_session_id'
+      });
+      
+      await queryInterface.addIndex('quiz_session_questions', ['question_id'], {
+        name: 'idx_quiz_session_questions_question_id'
+      });
+      
+      await queryInterface.addIndex('quiz_session_questions', ['quiz_session_id', 'question_order'], {
+        name: 'idx_quiz_session_questions_session_order'
+      });
+      
+      // Unique constraint to prevent duplicate questions in same session
+      await queryInterface.addIndex('quiz_session_questions', ['quiz_session_id', 'question_id'], {
+        name: 'idx_quiz_session_questions_session_question_unique',
+        unique: true
+      });
+      
+      console.log('✅ Performance indexes added successfully');
+      
+    } catch (error) {
+      console.error('❌ Error adding indexes:', error);
+      throw error;
+    }
+  },
+
+  down: async (queryInterface, Sequelize) => {
+    console.log('Removing performance indexes...');
+    
+    try {
+      // Remove QuizSession indexes
+      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_user_id');
+      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_guest_session_id');
+      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_category_id');
+      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_status');
+      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_created_at');
+      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_user_created');
+      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_guest_created');
+      await queryInterface.removeIndex('quiz_sessions', 'idx_quiz_sessions_category_status');
+      
+      // Remove QuizSessionQuestion indexes
+      await queryInterface.removeIndex('quiz_session_questions', 'idx_quiz_session_questions_session_id');
+      await queryInterface.removeIndex('quiz_session_questions', 'idx_quiz_session_questions_question_id');
+      await queryInterface.removeIndex('quiz_session_questions', 'idx_quiz_session_questions_session_order');
+      await queryInterface.removeIndex('quiz_session_questions', 'idx_quiz_session_questions_session_question_unique');
+      
+      console.log('✅ Performance indexes removed successfully');
+      
+    } catch (error) {
+      console.error('❌ Error removing indexes:', error);
+      throw error;
+    }
+  }
+};