Details

1. My Contributions
   • Implemented project-based late-night self-study applications. A student enters the date, time, and project details, selects team members, and submits the application.
   • When a student applies or a teacher changes the status (accept/reject), the application status of all participants, including the project leader, had to be updated together.
2. Initial Table Structure
   • An individual late-night self-study feature already existed. During MVP development, we reused the existing general late-night self-study table and created a separate project table that stored the project ID as a foreign key.
   

   
3. Problems
   • Unnecessary WHERE clauses were generated when querying projects. Whenever JPA looked up self-study records, it had to distinguish the self-study type by the presence of project_id, which added redundant WHERE conditions to every request.
   • Frequent loops and repeated SQL queries led to the JPA N+1 problem and high time complexity.
4. Improved Table Structure
   • Normalized the schema into night_study, night_study_project, and night_study_project_member tables.
   • Rather than relying on loops, I reduced time complexity by using IN, JOIN, and EXISTS in JPA and JPQL.
   

   

   
5. Results
   • Reduced response times from an average of 320ms to 87ms for POST requests and from 624ms to 49ms for PATCH requests.
   • Eliminated the unnecessary queries (JOINs, WHERE clauses, etc.) that had been generated when querying projects.
6. Before Refactoring
   

   

   
7. After Refactoring