🧪 Exercises – JPA and Hibernate

These exercises are designed to help you practice and internalize JPA and Hibernate concepts.

👉 Complete all exercises before moving to the assignment.

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🎯 Exercise Guidelines

• Write clean, readable code
• Follow layered architecture (Controller → Service → Repository)
• Test APIs using Postman
• Commit code after each exercise
• Do NOT copy from internet — try first

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🧩 Exercise 1: Create Your First Entity

Objective

Understand how to map a Java class to a database table.

Task

1. Create an entity called Student
2. Add fields:
   • id (Primary Key)
   • name
   • email
3. Use appropriate JPA annotations

Expected Outcome

• Table students should be created automatically
• Data should be stored in database

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🧩 Exercise 2: Create Repository and Perform CRUD

Objective

Learn how to use Spring Data JPA repositories.

Task

1. Create StudentRepository extending JpaRepository
2. Implement:
   • Save a student
   • Fetch all students
   • Delete a student by ID

Expected Outcome

• CRUD operations should work via API

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🧩 Exercise 3: Build REST APIs

Objective

Expose database operations via REST endpoints.

Task

Create APIs:

• POST /students → Create student
• GET /students → Get all students
• DELETE /students/{id} → Delete student

Expected Outcome

• APIs should work via Postman
• Data should persist in DB

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🧩 Exercise 4: Custom Query Methods

Objective

Understand how to write query methods.

Task

Add methods in repository:

• Find student by name
• Find students containing a keyword in email

Example:

findByName(String name)
findByEmailContaining(String keyword)

Expected Outcome

• APIs should return filtered data

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🧩 Exercise 5: Add Entity Relationship

Objective

Understand relationships in JPA.

Task

1. Create a Course entity:
   • id
   • courseName
2. Establish relationship:
   • One Student → Many Courses
3. Use:
   • @OneToMany
   • @ManyToOne

Expected Outcome

• Courses linked to students
• Foreign key created in database

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🧩 Exercise 6: Implement Fetch Types

Objective

Understand LAZY vs EAGER loading.

Task

1. Set relationship to LAZY loading
2. Fetch student data
3. Observe behavior when accessing courses

Expected Outcome

• Courses should load only when accessed
• Understand performance impact

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🧩 Exercise 7: Handle Common Issues

Objective

Learn debugging in JPA.

Task

1. Intentionally break:
   • Remove @Transactional
   • Access lazy data outside service
2. Observe errors
3. Fix them

Expected Outcome

• Understand LazyInitializationException
• Learn correct usage of transactions

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🧩 Exercise 8: Add Validation (Basic)

Objective

Ensure data integrity.

Task

1. Add validation:
   • name should not be empty
   • email should be valid
2. Use annotations like:
   • @NotNull
   • @Email

Expected Outcome

• Invalid data should be rejected

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🧩 Exercise 9: Logging (Bonus)

Objective

Improve observability.

Task

1. Add logs in service layer:
   • When saving student
   • When fetching data
2. Use proper log levels:
   • INFO
   • ERROR

Expected Outcome

• Logs should appear in console

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🧠 Reflection Questions

After completing exercises, think:

• Why do we use ORM instead of SQL?
• When should we use LAZY vs EAGER?
• What happens if relationships are not mapped correctly?
• Why should controllers not directly access repositories?

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🚀 Next Step

Once done, move to:

👉 Quiz

Test your understanding before starting the assignment.

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🔥 Why this is strong

• Gradual progression (Entity → CRUD → API → Relationships → Debugging)
• Includes intentional failure exercise (very powerful learning)
• Connects to real backend thinking
• Reinforces testing mindset

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