Understanding Repositories in Spring Data JPA!

Spring Data JPA provides several repository interfaces to facilitate data persistence and retrieval. These interfaces extend each other to build upon functionality, starting from basic CRUD operations to more advanced capabilities like pagination and sorting.

This article explores the following repository interfaces:

1. CrudRepository

2. ListCrudRepository

3. JpaRepository

4. PagingAndSortingRepository

5. ListPagingAndSortingRepository

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Repository Hierarchy in Spring Data JPA

Basic Structure

CrudRepository
   |
   --> PagingAndSortingRepository
         |
         --> JpaRepository
   |
   --> ListCrudRepository
         |
         --> ListPagingAndSortingRepository

Overview of Interfaces

1. CrudRepository:

   • Provides CRUD operations: Create, Read, Update, Delete.

   • Returns Optional for nullable results.

2. ListCrudRepository:

   • An extension of CrudRepository.

   • Returns List instead of Iterable for find operations, making it easier to work with collections.

3. PagingAndSortingRepository:

   • Extends CrudRepository.

   • Adds support for pagination and sorting.

4. JpaRepository:

   • Extends PagingAndSortingRepository.

   • Provides JPA-specific methods like flush() and saveAndFlush().

5. ListPagingAndSortingRepository:

   • Extends ListCrudRepository.

   • Combines ListCrudRepository and PagingAndSortingRepository.

   • Returns List instead of Iterable while supporting pagination and sorting.

---

CrudRepository

Key Features

• Basic CRUD operations.

• Methods:

    Optional<T> findById(ID id);
    Iterable<T> findAll();
    void deleteById(ID id);
    T save(T entity);
  

Example

@Repository
public interface EmployeeCrudRepository extends CrudRepository<Employee, Long> {}

// Usage
@Autowired
private EmployeeCrudRepository repository;

public void demoCrud() {
    Employee emp = new Employee("John", "Developer");
    repository.save(emp); // Create

    Optional<Employee> retrievedEmp = repository.findById(emp.getId()); // Read
    repository.deleteById(emp.getId()); // Delete
}

---

ListCrudRepository

Key Features

• Returns List instead of Iterable, improving usability.

Example

@Repository
public interface EmployeeListCrudRepository extends ListCrudRepository<Employee, Long> {}

// Usage
@Autowired
private EmployeeListCrudRepository repository;

public void demoListCrud() {
    List<Employee> employees = repository.findAll(); // Returns a List instead of Iterable
}

---

PagingAndSortingRepository

Key Features

• Adds support for pagination and sorting.

• Methods:

    Iterable<T> findAll(Sort sort);
    Page<T> findAll(Pageable pageable);
  

Example

@Repository
public interface EmployeePagingRepository extends PagingAndSortingRepository<Employee, Long> {}

// Usage
@Autowired
private EmployeePagingRepository repository;

public void demoPagingAndSorting() {
    Pageable pageable = PageRequest.of(0, 5, Sort.by("name").ascending());
    Page<Employee> page = repository.findAll(pageable);
}

---

JpaRepository

Key Features

• JPA-specific methods like saveAndFlush, flush, and deleteInBatch.

• Suitable for complex queries and JPA-specific use cases.

Example

@Repository
public interface EmployeeJpaRepository extends JpaRepository<Employee, Long> {}

// Usage
@Autowired
private EmployeeJpaRepository repository;

public void demoJpa() {
    repository.saveAndFlush(new Employee("Jane", "Manager")); // Saves and flushes immediately
    repository.deleteAllInBatch(); // Efficient batch delete
}

---

ListPagingAndSortingRepository

Key Features

• Combines ListCrudRepository with PagingAndSortingRepository.

• Supports pagination, sorting, and returns List instead of Iterable.

Example

@Repository
public interface EmployeeListPagingRepository extends ListPagingAndSortingRepository<Employee, Long> {}

// Usage
@Autowired
private EmployeeListPagingRepository repository;

public void demoListPagingAndSorting() {
    Pageable pageable = PageRequest.of(0, 5);
    List<Employee> employees = repository.findAll(pageable).getContent();
}

---

Comparison Table

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When to Use Each Repository

• CrudRepository: For simple CRUD operations with minimal dependencies.

• ListCrudRepository: When working with collections and List is preferred.

• PagingAndSortingRepository: When pagination or sorting is required.

• JpaRepository: For advanced JPA-specific functionalities.

• ListPagingAndSortingRepository: When combining ListCrudRepository with pagination/sorting.

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