CRUD methods (save, findById, findAll, delete) in Spring Boot

Introduction

CRUD methods help you create, read, update, and delete data easily in your app. They make working with databases simple and organized.

When you want to add new data to your database.

When you need to get data by its unique ID.

When you want to list all data entries.

When you want to remove data from the database.

Syntax

Spring Boot

save(entity) - saves or updates an entity in the database
findById(id) - finds an entity by its ID
findAll() - retrieves all entities
delete(entity) - deletes an entity from the database

These methods are usually part of Spring Data JPA repositories.

They handle database operations without writing SQL.

Examples

Saves a new user or updates an existing one.

Spring Boot

repository.save(user);

Finds a user with ID 1. Returns Optional to handle if user is missing.

Spring Boot

Optional<User> user = repository.findById(1L);

Gets a list of all users in the database.

Spring Boot

List<User> users = repository.findAll();

Deletes the given user from the database.

Spring Boot

repository.delete(user);

Sample Program

This Spring Boot app shows how to use CRUD methods with a User entity. It saves a user, finds it by ID, lists all users, and deletes the user.

Spring Boot

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import java.util.List;
import java.util.Optional;

@SpringBootApplication
public class CrudDemoApplication {
    public static void main(String[] args) {
        var context = SpringApplication.run(CrudDemoApplication.class, args);
        UserRepository repository = context.getBean(UserRepository.class);

        // Create and save a new user
        User user = new User(1L, "Alice");
        repository.save(user);

        // Find user by ID
        Optional<User> foundUser = repository.findById(1L);
        System.out.println("Found user: " + foundUser.orElse(null));

        // Find all users
        List<User> allUsers = repository.findAll();
        System.out.println("All users: " + allUsers);

        // Delete user
        repository.delete(user);
        System.out.println("User deleted.");
    }
}

@Entity
record User(@Id Long id, String name) {}

@Repository
interface UserRepository extends JpaRepository<User, Long> {}

Important Notes

Use Optional from findById to safely handle missing data.

Spring Data JPA automatically implements these methods for you.

Deleting an entity removes it permanently from the database.

Summary

CRUD methods let you manage data easily in Spring Boot.

Use save to add or update data.

Use findById, findAll, and delete to read and remove data.

Practice

1. Which Spring Boot repository method is used to add a new entity or update an existing one in the database?

easy

A. save()

B. findById()

C. delete()

D. findAll()

Solution

1. Step 1: Understand the purpose of save()

   The save() method is designed to add a new entity or update an existing one in the database.

2. Step 2: Compare with other methods

   findById() and findAll() are for reading data, and delete() is for removing data, so they do not add or update.

3. Final Answer:

   save() -> Option A

4. Quick Check:

   Add or update data = save() [OK]

Hint: Remember: save = add or update data [OK]

Common Mistakes:

• Confusing save() with findById()
• Thinking delete() adds data
• Using findAll() to save data

2. Which of the following is the correct syntax to find an entity by its ID using Spring Boot's repository?

easy

A. repository.findById(id);

B. repository.save(id);

C. repository.delete(id);

D. repository.findAll(id);

Solution

1. Step 1: Identify the method to find by ID

   The method findById(id) is used to retrieve an entity by its ID.

2. Step 2: Check syntax correctness

   repository.findById(id); is the correct syntax. Other methods do not accept an ID to find an entity.

3. Final Answer:

   repository.findById(id); -> Option A

4. Quick Check:

   Find by ID syntax = repository.findById(id) [OK]

Hint: Use findById(id) to get one entity by its ID [OK]

Common Mistakes:

• Using save() to find an entity
• Passing ID to findAll(), which takes no parameters
• Using delete() to find data

3. Given the following code snippet, what will allUsers.size() return if the database has 3 user records?

List<User> allUsers = userRepository.findAll();
int count = allUsers.size();

medium

A. 0

B. 3

C. 1

D. null

Solution

1. Step 1: Understand findAll() behavior

   The findAll() method returns a list of all entities in the database.

2. Step 2: Count the number of records returned

   If the database has 3 user records, allUsers will contain 3 elements, so allUsers.size() returns 3.

3. Final Answer:

   3 -> Option B

4. Quick Check:

   findAll() returns all records count = 3 [OK]

Hint: findAll() returns all records as a list [OK]

Common Mistakes:

• Assuming findAll() returns null if no records
• Confusing size() with findById() result
• Thinking findAll() returns a single entity

4. What is wrong with this code snippet if it throws a compilation error?

userRepository.delete(5);

Assuming delete expects an entity object, not an ID.

medium

A. The ID must be a string, not an integer.

B. The method delete does not exist in Spring Boot repositories.

C. You must pass an entity object, not an ID, to delete.

D. You should use deleteById(5) instead to delete by ID.

Solution

1. Step 1: Understand delete method signature

   The delete method expects an entity object, not just an ID.

2. Step 2: Use correct method to delete by ID

   To delete by ID, use deleteById(id) method instead of delete(id).

3. Final Answer:

   You should use deleteById(5) instead to delete by ID. -> Option D

4. Quick Check:

   Delete by ID = deleteById(id) [OK]

Hint: Use deleteById(id) to remove by ID, not delete(entity) [OK]

Common Mistakes:

• Passing ID to delete() instead of entity
• Assuming delete() accepts ID directly
• Using wrong data type for ID

5. You want to update a user's email in the database using Spring Boot. Which sequence of repository methods correctly achieves this?

// Assume userId and newEmail are given
Optional<User> userOpt = userRepository.findById(userId);
if (userOpt.isPresent()) {
    User user = userOpt.get();
    user.setEmail(newEmail);
    // What next?
}

hard

A. Call userRepository.delete(user); then save(user);.

B. Call userRepository.findAll(); to refresh the list.

C. Call userRepository.save(user); to update the user.

D. No need to call any method; changes auto-save.

Solution

1. Step 1: Retrieve the user entity by ID

   The code uses findById(userId) to get the user object.

2. Step 2: Update the user and save changes

   After setting the new email, calling save(user) updates the database record.

3. Final Answer:

   Call userRepository.save(user); to update the user. -> Option C

4. Quick Check:

   Update data = findById + modify + save [OK]

Hint: Update entity fields then call save() to persist changes [OK]

Common Mistakes:

• Assuming changes auto-save without calling save()
• Deleting before saving to update
• Using findAll() to update a single record