Article 8: Spring Data JPA Repositories (CRUD Made Easy)

1. Introduction

Now that your database and entity are ready, the next question is:

How do we save, read, update, and delete data?

Spring Data JPA answers this with repositories — no boilerplate SQL, no manual DAO code.

This article shows how CRUD becomes almost effortless.

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2. What Is a Repository?

A repository is a data access layer abstraction.

Instead of writing:

• SQL queries
• JDBC code
• EntityManager boilerplate

You simply define an interface.

Spring generates the implementation automatically.

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3. JpaRepository Basics

Spring Data provides multiple base interfaces. The most commonly used is:

JpaRepository<T, ID>

Where:

• T → Entity type
• ID → Primary key type

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4. Creating Your First Repository

4.1 Create Repository Package

com.example.demo.repository

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4.2 Create UserRepository

package com.example.demo.repository;

import com.example.demo.model.User;
import org.springframework.data.jpa.repository.JpaRepository;

public interface UserRepository extends JpaRepository<User, Long> {
}

That’s it. No implementation needed.

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5. Built-in CRUD Methods

JpaRepository already provides:

Method	Purpose
save()	Create / Update
findById()	Find by ID
findAll()	Fetch all
deleteById()	Delete
count()	Count records

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6. Using Repository in Service Layer

@Service
public class UserService {

    private final UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    public User createUser(User user) {
        return userRepository.save(user);
    }

    public List<User> getAllUsers() {
        return userRepository.findAll();
    }
}

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7. Exposing CRUD APIs

@RestController
@RequestMapping("/users")
public class UserController {

    private final UserService userService;

    public UserController(UserService userService) {
        this.userService = userService;
    }

    @PostMapping
    public User create(@RequestBody User user) {
        return userService.createUser(user);
    }

    @GetMapping
    public List<User> getAll() {
        return userService.getAllUsers();
    }
}

Test using Postman or curl.

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8. Derived Query Methods (Magic ✨)

Spring Data can derive queries from method names.

Example:

List<User> findByName(String name);
User findByEmail(String email);

No SQL required.

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9. Custom Queries Using @Query

@Query("SELECT u FROM User u WHERE u.email LIKE %:email%")
List<User> searchByEmail(@Param("email") String email);

Use when:

• Complex queries
• Joins
• Performance tuning

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10. Pagination & Sorting

Page<User> findAll(Pageable pageable);

Usage:

PageRequest.of(0, 5, Sort.by("name"));

Essential for real applications.

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11. Common Beginner Mistakes

❌ Putting logic in controller
❌ Forgetting @Service
❌ Wrong generic types
❌ Not handling Optional

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12. What You Should Understand Before Moving On

You should now know:

• What repositories are
• How JpaRepository works
• How CRUD APIs are built
• How query methods work

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13. What’s Next?

➡ Article 9: Database Migrations with Flyway

• Schema versioning
• Controlled DB changes
• Production-safe migrations

Type Next when you’re ready.