markdown Spring：MongoDB

Posted 2021-05-05

- `@Document`: Identifies a domain object to be persisted to MongoDB.
- `@Id`: Demarcates an identifier.
- `@Indexed(unique = true)`: Mark a field to be indexed using MongoDB's indexing feature.
- `@TextIndexed`: marks a field to be part of the text index. As there can be only one text index per collection all fields marked with {@link TextIndexed} are combined into one single index.
- `@TextScore`: marks the property to be considered as the on server calculated when doing full text search. Property will not be written when saving entity.
- `@DBRef`: creates a reference with a document saved on another collection.

``` java
@Document(collection = "users")
public class User {

    @Id
    private String id;

    @Indexed(unique = true)
    private String username;

    @TextIndexed
    private String firstname;

    @TextIndexed
    private String lastname;

    @TextScore
    private Float textScore;

    private Address homeAddress;

    @DBRef
    private EmailAddress email;
  }
```

- Extend `CrudRepository` or `PagingAndSortRepository`
- main functionalities:
  - `<S extends T> S save(S entity)`
  - `Optional<T> findById(ID primaryKey)`
  - `Iterable<T> findAll()`
  - `long count()`
  - `void delete(T entity)`
  - `boolean existsById(ID primaryKey)`
  - `Iterable<T> findAll(Sort sort)`
  - `Page<T> findAll(Pageable pageable)`
- Support json query
 
``` java
public interface UserRepository extends PagingAndSortingRepository<User, String> {

    Page<User> findAllByUsername(@Param("username") String username, Pageable page);
    Page<User> findAllByHomeAddress_City(@Param("city") String city, Pageable page);

    @Query(" {'homeAddress.country' : ?0 } ")
    Page<User> jsonQueryFindByCountry(String country, Pageable page);

    @Query(" { 'username' : ?0 } ")
    Page<User> jsonQueryFindUsernameByRegex(String regex, Pageable page);

    Optional<User> findByEmail_Id(String emailId);

}
```
```

- Extend `AbstractMongoEventListener<Document>`
- Override the propper method:
  - `onBeforeConvert(BeforeConvertEvent<E> event)`
  - `onBeforeSave(BeforeSaveEvent<E> event) `: get entity calling `event.getSource`. Note: it may not have an `id`.
  - `onAfterSave(AfterSaveEvent<E> event)`: get entity calling `event.getSource`.
  - `onAfterLoad(AfterLoadEvent<E> event)`
  - `onAfterConvert(AfterConvertEvent<E> event)`
  - `onAfterDelete(AfterDeleteEvent<E> event)`
  - `onBeforeDelete(BeforeDeleteEvent<E> event)`: get `id` calling:
``` java
public void onAfterSave(AfterSaveEvent<T> event) {
  Document courseClassDoc = event.getSource();
  String classID = courseClassDoc.get("_id").toString();
}
```
- Create a `@Bean` with the listener on a `@Configuration` file
 
## Listener
``` java
public class UserListener extends AbstractMongoEventListener<User> {

    @Autowired
    private EmailRepository emailRepository;

    @Override
    public void onAfterSave(AfterSaveEvent<User> event) {
        User user = event.getSource();
        if (user.getEmail() != null && user.getEmail().getId() != null) {
            Optional<EmailAddress> email = emailRepository.findById(user.getEmail().getId());
            if ( email.isPresent() && !email.get().equals(user.getEmail()) ) {
                EmailAddress updatedEmail = user.getEmail();
                emailRepository.save(updatedEmail);
            }
        }
        super.onAfterSave(event);
    }
}
```

## Configuration
``` java
@Configuration
public class MongoConfig {
    @Bean
    public UserListener userListener() {
        return new UserListener();
    }
}
```

``` groove
dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-mongodb'
    testImplementation 'de.flapdoodle.embed:de.flapdoodle.embed.mongo'
}
```