MODULE 6 - Advanced Spring Data JPA

Welcome to Module 6! 🎯

In Module 2, you learned the basics of Spring Data JPA: the 4 CRUD methods (save, findById, findAll, deleteById) and 3 simple keywords (findBy, And, Or).

Now, you are ready to go further!

This module teaches you advanced JPA concepts to create complex queries and manage entity relationships.

🎓 Learning Objectives

By the end of this module, you will be able to:

✅ Use the 15+ Spring Data JPA keywords
✅ Create custom queries with @Query
✅ Manage relationships (@OneToMany, @ManyToOne, @ManyToMany)
✅ Use pagination and sorting
✅ Optimize query performance

📚 Prerequisites

Before starting this module, you should have:

✅ Completed Modules 1 to 4
✅ Mastered the basics of JPA (Module 2, Chapter 5)
✅ Understood repositories (JpaRepository)

If these prerequisites are not met, go back to Module 2!

🗺️ Module Outline

Theoretical Part (4 chapters)

Chapter 1: Advanced Naming Conventions

Duration: 1h

Content:

The 15+ Spring Data JPA keywords
Between, LessThan, GreaterThan
Like, StartingWith, EndingWith, Containing
In, NotIn, IsNull, IsNotNull
True, False, IgnoreCase
Practical examples for each keyword

Why important? Create complex queries without writing SQL

Chapter 2: Entity Relationships

Duration: 1h30

Content:

@OneToOne (1-1)
@OneToMany and @ManyToOne (1-N)
@ManyToMany (N-N)
Fetch types (LAZY vs EAGER)
Cascade operations
Bidirectional relationships

Why important? Model complex real-world data

Chapter 3: Custom Queries with @Query

Duration: 1h

Content:

JPQL syntax
@Query with JPQL
@Query with native SQL
Named parameters with @Param
Named queries
Dynamic queries

Why important? Go beyond naming conventions

Chapter 4: Pagination and Performance

Duration: 1h

Content:

Pageable and Page<T>
Sort and multi-criteria sorting
N+1 problem
Fetch strategies
Projections
Query optimization

Why important? Create high-performance applications

Practical Part (3 Labs)

Lab 6.1: Advanced Conventions

Duration: 2h

Objective: Master the 15+ keywords

You will create:

Product entity with many fields
20 repository methods using the keywords
Tests for each method

Lab 6.2: Employee-Department Relationships

Duration: 2h

Objective: Manage entity relationships

You will create:

Employee and Department entities (OneToMany/ManyToOne)
Complete CRUD with relationships
Cascade operations
Relationship tests

Lab 6.3: Airport-Flight-Passenger Exercise

Duration: 2h30

Objective: Comprehensive assessment

You will:

Model 3 related entities
Implement 20 queries (Easy, Medium, Hard)
Provided solution guide
Self-assessment

📊 Total Duration

Type	Duration
Theory	4h30 (4 chapters)
Practice	6h30 (3 Labs)
Total	11h (~3-4 sessions)

🎯 What You Will Learn

Before Module 6

// You knew how to do this:
public interface ProductRepository extends JpaRepository<Product, Long> {
    List<Product> findByName(String name);
    List<Product> findByNameAndPrice(String name, Double price);
}

Limited to: Simple queries with And and Or

After Module 6

// You will know how to do all this:
public interface ProductRepository extends JpaRepository<Product, Long> {
    
    // Comparisons
    List<Product> findByPriceBetween(Double min, Double max);
    List<Product> findByPriceLessThan(Double maxPrice);
    List<Product> findByPriceGreaterThanEqual(Double minPrice);
    
    // Text search
    List<Product> findByNameContaining(String keyword);
    List<Product> findByNameStartingWith(String prefix);
    List<Product> findByDescriptionLike(String pattern);
    
    // Lists and nulls
    List<Product> findByCategoryIn(List<String> categories);
    List<Product> findByDiscountIsNull();
    List<Product> findByActiveTrue();
    
    // Sorting and pagination
    Page<Product> findByCategory(String category, Pageable pageable);
    
    // Custom queries
    @Query("SELECT p FROM Product p WHERE p.price < :maxPrice")
    List<Product> findCheapProducts(@Param("maxPrice") Double maxPrice);
    
    // Native SQL
    @Query(value = "SELECT * FROM products WHERE stock < 10", nativeQuery = true)
    List<Product> findLowStock();
}

You will master: Complex queries, relationships, performance!

🚀 Why This Module Is Important

1. Real-World Queries in Production

In a company, you will NOT only do findAll(). You will need to:

// Find a customer's orders in the last 30 days
List<Order> findByCustomerIdAndOrderDateAfter(Long customerId, LocalDate date);

// Out-of-stock products in a category
List<Product> findByCategoryAndStockLessThan(String category, Integer minStock);

// Employees in a department with salary in a range
List<Employee> findByDepartmentAndSalaryBetween(Department dept, Double min, Double max);

This module prepares you for reality!

2. Application Performance

Common issue: The N+1 Problem

// ❌ Bad practice - N+1 queries!
List<Department> departments = departmentRepo.findAll();  // 1 query
for (Department dept : departments) {
    List<Employee> employees = dept.getEmployees();  // N queries!
    // ...
}

Solution you will learn:

// ✅ Good practice - 1 query!
@Query("SELECT d FROM Department d JOIN FETCH d.employees")
List<Department> findAllWithEmployees();

This module teaches you to write performant code!

3. Modeling Complex Data

Real case: E-commerce

Customer ──< Order >── Product
              │
              └──> Payment

You will learn to:

Model these relationships
Manage cascades (delete a Customer → their Orders?)
Optimize queries
Handle orphaned data

🗺️ Training Progression

Module 2: JPA Basics (4 methods, 3 simple keywords)
          ↓
Module 6: ← YOU ARE HERE - Advanced JPA
          (15+ keywords, relationships, @Query, performance)
          ↓
Projects: Complete applications with complex databases

Module 6 = Becoming an expert in Spring Data JPA!

📖 How to Approach This Module

Recommended Method

Read the chapters in order
- Chapter 1: Conventions (15+ keywords)
- Chapter 2: Relationships (OneToMany, ManyToOne, etc.)
- Chapter 3: @Query (JPQL, native SQL)
- Chapter 4: Performance (pagination, optimization)
Do the labs progressively
- Lab 6.1: Practice conventions (2h)
- Lab 6.2: Practice relationships (2h)
- Lab 6.3: Comprehensive assessment (2h30)
Test all the code
- Do not copy, type the code
- Test each query
- Understand the results

Recommended Time

Intensive Option (1 weekend):

Saturday: Chapters 1-2 + Lab 6.1
Sunday: Chapters 3-4 + Lab 6.2 + Lab 6.3

Progressive Option (3 sessions):

Session 1: Chapters 1-2 + Lab 6.1
Session 2: Chapter 3 + Lab 6.2
Session 3: Chapter 4 + Lab 6.3

✅ Self-Assessment

Before starting, test your knowledge:

Do you know how to create a findByPriceBetween method? ☐ Yes ☐ No
Are you familiar with @OneToMany and @ManyToOne? ☐ Yes ☐ No
Do you know how to use @Query? ☐ Yes ☐ No
Do you understand the N+1 problem? ☐ Yes ☐ No
Do you know how to paginate results? ☐ Yes ☐ No

If you answered "No" to 2 or more questions → This module is ESSENTIAL for you!

After the module, retake this test. You should answer "Yes" everywhere!

🎯 Next Step

Ready to become an expert in Spring Data JPA?

➡️ Start with Chapter 1: Advanced Naming Conventions

⬅️ Back to Course Outline

Welcome to Module 6! 🎯​

🎓 Learning Objectives​

📚 Prerequisites​

🗺️ Module Outline​

Theoretical Part (4 chapters)​

Chapter 1: Advanced Naming Conventions​

Chapter 2: Entity Relationships​

Chapter 3: Custom Queries with @Query​

Chapter 4: Pagination and Performance​

Practical Part (3 Labs)​

Lab 6.1: Advanced Conventions​

Lab 6.2: Employee-Department Relationships​

Lab 6.3: Airport-Flight-Passenger Exercise​

📊 Total Duration​

🎯 What You Will Learn​

Before Module 6​

After Module 6​

🚀 Why This Module Is Important​

1. Real-World Queries in Production​

2. Application Performance​

3. Modeling Complex Data​

🗺️ Training Progression​

📖 How to Approach This Module​

Recommended Method​

Recommended Time​

✅ Self-Assessment​

🎯 Next Step​

Welcome to Module 6! 🎯

🎓 Learning Objectives

📚 Prerequisites

🗺️ Module Outline

Theoretical Part (4 chapters)

Chapter 1: Advanced Naming Conventions

Chapter 2: Entity Relationships

Chapter 3: Custom Queries with @Query

Chapter 4: Pagination and Performance

Practical Part (3 Labs)

Lab 6.1: Advanced Conventions

Lab 6.2: Employee-Department Relationships

Lab 6.3: Airport-Flight-Passenger Exercise

📊 Total Duration

🎯 What You Will Learn

Before Module 6

After Module 6

🚀 Why This Module Is Important

1. Real-World Queries in Production

2. Application Performance

3. Modeling Complex Data

🗺️ Training Progression

📖 How to Approach This Module

Recommended Method

Recommended Time

✅ Self-Assessment

🎯 Next Step