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Reactive Data Access Needs

Introducing Reactive Data Stores

Setting Up Reactive MongoDB

Defining Reactive Entities

import org.springframework.data.annotation.Id;
import org.springframework.data.mongodb.core.mapping.Document;

@Document(collection = "products")
public class Product {
  @Id
  private String id;
  private String name;
  private double price;

  public Product(String id, String name, double price) {
    this.id = id;
    this.name = name;
    this.price = price;
  }

  // Getters and Setters (omitted for brevity)
  public String getId() { return id; }
  public String getName() { return name; }
  public double getPrice() { return price; }

  @Override
  public String toString() {
    return "Product{id='" + id + "', name='" + name + "'}";
  }
}

Creating Reactive Repositories

import org.springframework.data.mongodb.repository.ReactiveMongoRepository;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

public interface ProductRepository extends ReactiveMongoRepository<Product, String> {
  // Custom reactive query methods can be added here
  Mono<Product> findByName(String name);
  Flux<Product> findByPriceGreaterThan(double price);
}

Simulating Reactive Save

import reactor.core.publisher.Mono;

class Item {
  String id;
  String name;
  public Item(String id, String name) {
    this.id = id;
    this.name = name;
  }
  @Override
  public String toString() { return "Item{name='" + name + "'} "; }
}

public class Main {
  public static void main(String[] args) {
    Item newItem = new Item("101", "Reactive Widget");

    // Simulate a reactive repository save method
    Mono<Item> savedItemMono = Mono.just(newItem)
                                   .doOnSuccess(item -> System.out.println("Simulating DB save for: " + item.name));

    System.out.println("Initiating save operation...");
    savedItemMono.subscribe(
      item -> System.out.println("Saved item received: " + item),
      error -> System.err.println("Error: " + error.getMessage()),
      () -> System.out.println("Save process completed.")
    );
  }
}

Simulating Reactive Retrieval

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import java.util.Arrays;
import java.util.List;

class User {
  String id;
  String name;
  public User(String id, String name) {
    this.id = id;
    this.name = name;
  }
  @Override
  public String toString() { return "User{name='" + name + "'} "; }
}

public class Main {
  public static void main(String[] args) {
    List<User> users = Arrays.asList(
      new User("U1", "Alice"),
      new User("U2", "Bob"),
      new User("U3", "Charlie")
    );

    // Simulate finding a single user by ID
    Mono<User> userMono = Mono.just(users.get(0));
    System.out.println("\n--- Finding single user ---");
    userMono.subscribe(user -> System.out.println("Found: " + user));

    // Simulate finding all users
    Flux<User> userFlux = Flux.fromIterable(users);
    System.out.println("\n--- Finding all users ---");
    userFlux.subscribe(user -> System.out.println("Found: " + user));
  }
}

Integrating with Reactive Services

import reactor.core.publisher.Mono;
// Assume Product and ProductRepository are defined elsewhere
// import your.package.Product;
// import your.package.ProductRepository;

// This is a simplified example, not a full runnable app
// as it would require a full Spring Boot context.
class ProductService {
  private final ProductRepository productRepository;

  public ProductService(ProductRepository productRepository) {
    this.productRepository = productRepository;
  }

  public Mono<String> createProduct(Product product) {
    return productRepository.save(product)
                            .map(Product::getId);
  }

  public Mono<Product> getProductById(String id) {
    return productRepository.findById(id);
  }
}

Chaining Reactive Data Operations

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import java.time.Duration;

public class Main {
  public static void main(String[] args) {
    // Simulate fetching user IDs from a database (Flux)
    Flux<String> userIds = Flux.just("userA", "userB", "userC");

    // Simulate fetching user details for each ID (Mono)
    Flux<String> userNames = userIds.delayElements(Duration.ofMillis(50))
                                    .flatMap(id -> Mono.just("Name_" + id.toUpperCase()));

    System.out.println("Fetching and transforming user data...");
    userNames.subscribe(
      name -> System.out.println("Processed User: " + name),
      error -> System.err.println("Error: " + error.getMessage()),
      () -> System.out.println("All users processed.")
    );

    // Keep main thread alive for async operations
    try { Thread.sleep(500); } catch (InterruptedException e) {} 
  }
}

Quick Check: Reactive Repositories

Recap: Reactive Data Access