CRUD REST API with PostgreSQL and Spring Boot

Introduction

CRUD is Create, Read, Update, Delete. A typical REST design uses POST create, GET read, PUT/PATCH update, DELETE remove. This post extends Item with an updatable name and a delete by id.

Real-world explanation

• Idempotent PUT — same request twice should leave the same resource (when possible)
• 204 No Content — common for delete or update with no body to return
• 404 — when the id is not in the database

Service: update + delete

@Transactional
public Item updateName(Long id, String newName) {
  Item it = itemRepository.findById(id)
      .orElseThrow(() -> new IllegalArgumentException("not found"));
  it.setName(newName.trim());
  return it; // managed entity, flush on commit
}
 
@Transactional
public void delete(Long id) {
  if (!itemRepository.existsById(id)) {
    throw new IllegalArgumentException("not found");
  }
  itemRepository.deleteById(id);
}

Controller: REST mapping

@GetMapping("/{id}")
public ItemResponse get(@PathVariable Long id) {
  return itemRepository.findById(id)
      .map(ItemResponse::from)
      .orElseThrow(() -> new IllegalArgumentException("not found"));
}
 
@PutMapping("/{id}")
public ItemResponse replace(@PathVariable Long id, @RequestBody @Valid CreateItemRequest body) {
  return ItemResponse.from(itemService.updateName(id, body.name()));
}
 
@DeleteMapping("/{id}")
@ResponseStatus(HttpStatus.NO_CONTENT)
public void remove(@PathVariable Long id) {
  itemService.delete(id);
}

(Use a central not-found / problem response in the next error-handling article; here we keep exceptions for illustration.)

Folder structure (recap)

web/ItemController.java
service/ItemService.java
repository/ItemRepository.java
model/Item.java
dto/ItemResponse.java, CreateItemRequest.java, UpdateItemRequest.java (if fields differ)

Common mistakes

• Exposing all findAll() in production on a huge table without pagination (article 18)
• DELETE 200 with a body when no body is needed—204 is cleaner
• Losing concurrency control—later, optimistic locking with @Version if the same row is edited often

Best practices

• List with page and size (next article) in real APIs
• Consistent error shape for 404/400/409
• Integration tests: @SpringBootTest with Testcontainers PostgreSQL when the team is ready (optional, not the focus of this post)

Final summary

CRUD is wiring service and HTTP to JPA persistence with the right verbs and codes. Next: Bean Validation on DTOs.