spring-boot-crud-patterns

What this skill does

# Spring Boot CRUD Patterns

## Overview

Provides complete CRUD workflows for Spring Boot 3.5+ services using feature-focused architecture. Creates and validates domain aggregates, JPA repositories, application services, and REST controllers with proper separation of concerns. Defer detailed code listings to reference files for progressive disclosure.

## When to Use

- Create REST endpoints for create/read/update/delete workflows backed by Spring Data JPA.
- Implement feature packages following DDD-inspired architecture with aggregates, repositories, and application services.
- Define DTO records, request validation, and controller mappings for external clients.
- Diagnose CRUD regressions, repository contracts, or transaction boundaries in existing Spring Boot services.
- Trigger phrases: **"implement Spring CRUD controller"**, **"create an endpoint"**, **"add database entity"**, **"refine feature-based repository"**, **"map DTOs for JPA aggregate"**, **"add pagination to REST list endpoint"**.

## Instructions

Follow this streamlined workflow to deliver feature-aligned CRUD services with explicit validation gates:

### 1. Establish Feature Structure
Create `feature/<name>/` directories with `domain`, `application`, `presentation`, and `infrastructure` subpackages.
**Validate**: Verify directory structure matches the feature boundary before proceeding.

### 2. Define Domain Model
Create entity classes with invariants enforced through factory methods (`create`, `update`). Keep domain logic framework-free.
**Validate**: Assert all invariants are covered by unit tests before advancing.

### 3. Expose Domain Ports
Declare repository interfaces in `domain/repository` describing persistence contracts without implementation details.
**Validate**: Confirm interface signatures match domain operations.

### 4. Provide Infrastructure Adapter
Create JPA entities in `infrastructure/persistence` that map to domain models. Implement Spring Data repositories.
**Validate**: Run `@DataJpaTest` to verify entity mapping and repository integration.

### 5. Implement Application Services
Create `@Transactional` service classes that orchestrate domain operations and DTO mapping.
**Validate**: Ensure transaction boundaries are correct and optimistic locking is applied where needed.

### 6. Define DTOs and Controllers
Use Java records for API contracts with `jakarta.validation` annotations. Map REST endpoints with proper status codes.
**Validate**: Test validation constraints and verify HTTP status codes (201 POST, 200 GET, 204 DELETE).

### 7. Validate and Deploy
Run integration tests with Testcontainers. Verify migrations (Liquibase/Flyway) mirror the aggregate schema.
**Validate**: Execute full test suite before deployment; confirm schema migration scripts are applied.

See `references/examples-product-feature.md` for complete code aligned with each step.

## Examples

### Java Code Example: Product Feature

```java
// feature/product/domain/Product.java
package com.example.product.domain;

import java.math.BigDecimal;
import java.time.Instant;

public record Product(
    String id,
    String name,
    String description,
    BigDecimal price,
    int stock,
    Instant createdAt,
    Instant updatedAt
) {
    public static Product create(String name, String desc, BigDecimal price, int stock) {
        if (name == null || name.isBlank()) throw new IllegalArgumentException("Name required");
        if (price == null || price.compareTo(BigDecimal.ZERO) < 0) throw new IllegalArgumentException("Invalid price");
        return new Product(null, name.trim(), desc, price, stock, Instant.now(), null);
    }

    public Product withPrice(BigDecimal newPrice) {
        return new Product(id, name, description, newPrice, stock, createdAt, Instant.now());
    }
}
```

```java
// feature/product/domain/repository/ProductRepository.java
package com.example.product.domain.repository;

import com.example.product.domain.Product;
import java.util.Optional;

public interface ProductRepository {
    Product save(Product product);
    Optional<Product> findById(String id);
    void deleteById(String id);
}
```

```java
// feature/product/infrastructure/persistence/ProductJpaEntity.java
package com.example.product.infrastructure.persistence;

import jakarta.persistence.*;
import java.math.BigDecimal;
import java.time.Instant;

@Entity @Table(name = "products")
public class ProductJpaEntity {
    @Id @GeneratedValue(strategy = GenerationType.UUID)
    private String id;
    private String name;
    private String description;
    private BigDecimal price;
    private int stock;
    private Instant createdAt;
    private Instant updatedAt;

    // getters, setters, constructor from domain (omitted for brevity)
}
```

```java
// feature/product/infrastructure/persistence/JpaProductRepository.java
package com.example.product.infrastructure.persistence;

import com.example.product.domain.Product;
import com.example.product.domain.repository.ProductRepository;
import org.springframework.stereotype.Repository;

@Repository
public class JpaProductRepository implements ProductRepository {
    private final SpringDataProductRepository springData;

    public JpaProductRepository(SpringDataProductRepository springData) {
        this.springData = springData;
    }

    @Override
    public Product save(Product product) {
        ProductJpaEntity entity = toEntity(product);
        ProductJpaEntity saved = springData.save(entity);
        return toDomain(saved);
    }

    // findById, deleteById implementations...
}
```

```java
// feature/product/presentation/rest/ProductController.java
package com.example.product.presentation.rest;

import com.example.product.domain.Product;
import com.example.product.domain.repository.ProductRepository;
import jakarta.validation.Valid;
import jakarta.validation.constraints.*;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.*;

@RestController @RequestMapping("/api/products")
public class ProductController {
    private final ProductService service;

    public ProductController(ProductService service) { this.service = service; }

    @PostMapping
    public ResponseEntity<ProductResponse> create(@Valid @RequestBody CreateProductRequest req) {
        Product product = service.create(req.toDomain());
        return ResponseEntity.status(201).body(ProductResponse.from(product));
    }

    @GetMapping("/{id}")
    public ResponseEntity<ProductResponse> getById(@PathVariable String id) {
        return service.findById(id)
            .map(p -> ResponseEntity.ok(ProductResponse.from(p)))
            .orElse(ResponseEntity.notFound().build());
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> delete(@PathVariable String id) {
        service.deleteById(id);
        return ResponseEntity.noContent().build();
    }

    // record DTOs
    public record CreateProductRequest(
        @NotBlank String name,
        String description,
        @NotNull @DecimalMin("0.01") java.math.BigDecimal price,
        @Min(0) int stock
    ) {
        Product toDomain() { return Product.create(name, description, price, stock); }
    }

    public record ProductResponse(String id, String name, java.math.BigDecimal price) {
        static ProductResponse from(Product p) { return new ProductResponse(p.id(), p.name(), p.price()); }
    }
}
```

### JSON Input/Output Examples

**Create Request:**
```json
{
  "name": "Wireless Keyboard",
  "description": "Ergonomic keyboard",
  "price": 79.99,
  "stock": 50
}
```

**Created Response (201):**
```json
{
  "id": "prod-123",
  "name": "Wireless Keyboard",
  "price": 79.99,
  "_links": { "self": "/api/products/prod-123" }
}
```

**Paginated List Request:**
```bash
curl "http://localhost:8080/api/products?page=0&size=10&sort=name,asc"
```

## Best Practices

- Co-locate domain, application, and presentation code per aggregate within feature packages.
- Use Java records for immuta