data.adoc

Database access

1. Add the maven dependency

   <dependency>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-data-jpa</artifactId>
   </dependency>
   
   <dependency>
     <groupId>com.h2database</groupId>
     <artifactId>h2</artifactId>
     <scope>runtime</scope>
   </dependency>

2. Let’s define our domain object

   // simple jpa entity mapping
   @Entity
   class Book {
   
       @Id
       @GeneratedValue
       long id;
   
       private String title;
       private int year;
   
       protected Book() {} // mandates by JPA
   
       public Book(String title, int year) {
           this.title = title;
           this.year = year;
       }
   
       public long getId() { return id; }
   
       public String getTitle() { return title; }
   
       public int getYear() { return year; }
   
       @Override
       public String toString() {
           return "Book{id=" + id + ", title='" + title + '\'' + ", year=" + year + '}';
       }
   }
   
   // spring data implements this interface for us
   @Repository
   interface BookRepository extends JpaRepository<Book, Long> {}
   
   @RestController
   class BookController {
   
       @Autowired
       BookRepository repository;
   
       @RequestMapping("/b/{id}")
       Book getById(@PathVariable long id) {
           return repository.findOne(id);
       }
   }
   
   @Configuration
   class BookConfig {
   
       @Bean ApplicationRunner init(BookRepository repository) {
           // init db
           return args -> {
               repository.save(new Book("Java tutorial", 1995));
               repository.save(new Book("Spring reference", 2016));
           };
       }
   }

3. Restart your app and take a look at http://localhost:8080/b/1 expecting to see the json response

   {
     "id": 1,
     "title": "Java tutorial",
     "year": 1995
   }

4. (optional) Config your application to talk to a dedicated database (e.g. local MySQL)