A Full CRUD API with JPA

CRUD = the four basic actions

Almost every app does CRUD: Create, Read, Update, Delete. In a REST API each maps to an HTTP method (HTTP — HyperText Transfer Protocol — is the set of rules browsers and servers use to talk; its “methods” like GET and POST say what kind of action you want) on the same /products resource:

The full CRUD flow, in order

Picture using the finished API to manage one product from start to finish. Each step is one request, and each request runs one method in the controller below:

1. Create: send POST /products with a JSON body. The controller calls save(p) and the database gives the new row an id.
2. Read all: send GET /products. The controller calls findAll() and returns every row as a JSON array.
3. Read one: send GET /products/1. The controller reads the {id} from the URL and calls findById(1) to return just that row.
4. Update: send PUT /products/1 with new JSON. The controller sets the id from the URL and calls save(p), which overwrites that row.
5. Delete: send DELETE /products/1. The controller calls deleteById(1) and the row is gone.

The full controller

@RestController
@RequestMapping("/products")        // every URL below starts with /products
public class ProductController {
    private final ProductRepository repo;

    public ProductController(ProductRepository repo) {
        this.repo = repo;
    }

    @GetMapping                       // GET /products
    public List<Product> all() {
        return repo.findAll();
    }

    @GetMapping("/{id}")              // GET /products/5
    public Product one(@PathVariable Long id) {
        return repo.findById(id).orElseThrow();
    }

    @PostMapping                      // POST /products
    public Product create(@RequestBody Product p) {
        return repo.save(p);
    }

    @PutMapping("/{id}")              // PUT /products/5
    public Product update(@PathVariable Long id, @RequestBody Product p) {
        p.setId(id);                  // make sure we update the right row
        return repo.save(p);
    }

    @DeleteMapping("/{id}")           // DELETE /products/5
    public String delete(@PathVariable Long id) {
        repo.deleteById(id);
        return "Deleted product " + id;
    }
}

One nice helper

Notice @RequestMapping("/products") on the class. It sets a base path so every method’s URL starts with /products — you do not repeat it on each method.

Also notice findById(id).orElseThrow(). findById returns an Optional (it might be empty if the id does not exist). orElseThrow() turns an empty result into an error instead of a confusing null. Cleaner error handling comes in the next unit.