understand a SPRING DATA JPA (dao layer) project - java

I want to understand a project's DAO layer, it's developed with Spring Data JPA.
I will take the entity user as example. So I have this Interface named
userRepository extends JpaRepository<user, Long>
What's the (User, Long) for? And secondly
#Query("select u from user u where u.login = :login")
User findUserByLogin(#Param("login")String login);
I can't find an Implementation of this Interface in the project. Are we going to work with this Interface directly to get data from DB?

According to spring data jpa documentation:
The central interface in Spring Data repository abstraction is
Repository. It takes the domain class to manage as well as the
id type of the domain class as type arguments
So, Utilisateur, Long represents that your entity is Utilisateur and Long is the type of your primary key.
Regrading to your second question, spring offers default implmentations of those interfaces by creating proxy instances for them. Take a look at spring data docs.

Related

r2dbc ReactiveCrudRepository how to write JPQL/HQL

I'm new to Spring WebFlux reactive. I use R2DBC postgresql. I have a repository like that:
public interface BookRepository extends ReactiveCrudRepository<Book, Long> {
}
Now I want to add custom method to query by many complicated conditions:
public interface CustomBookRepository extends BookRepository {
Flux<Book> findByVeryComplicatedCondition(MyCriteriaDto criteria);
}
My implementation:
public class CustomBookRepositoryImpl extends CustomBookRepository {
//How to get it?
EntityManager em;
#Override
public Flux<Book> findByVeryComplicatedCondition(MyCriteriaDto criteria) {
Query query = em.createQuery("SELECT b from Book b WHERE (VERY COMPLICATED CONDITIONS)");
//What next?
}
}
My questions are in the code above:
How to obtain an EntityManager?
How to get Flux from HQL query I built?
When I ask these questions, I mean "How to do this with Spring reactive/r2dbc way", not "How to do this normal way with JDBC"
Spring Data R2DBC is not backed by a fully-fledged ORM framework like Hibernate. Therefore there are no such things as EntityManager and no possibility to write JQL/HQL queries.
However, one can still use native queries to define more complex methods, e.g.
interface MyRepository extends ReactiveCrudRepository<...> {
#Query("SELECT b from Book b WHERE (VERY COMPLICATED CONDITIONS)")
Flux<...> find(...);
}
If you want to use Hibernate/JPA JPQL like query in your project, consider Hibernate Reactive.
I have written an article to describe how to use Hibernate Reactive with Spring (BTW, I have contributed a patch to register SmallRye in Spring framework, so at the end of this article, you can skip to register MutinyAdapter in ReactiveAdapterRegistry ).
Spring Data has no plan to integrate Hibernate Reactive, so there is no Repository support.
Hibernate Reactive depends on Vertx reactive drivers, it does not support R2dbc.
HibernateReactive supports another ReactiveStreams implemetnation from Redhat - Smallrye Munity.

how annotation #Repository in java spring work? [duplicate]

This question already has answers here:
How are Spring Data repositories actually implemented?
(1 answer)
How does Spring Data JPA work internally
(1 answer)
Closed 3 years ago.
I have a code like this:
Repository
#Repository
public interface EquipmentRepository extends JpaRepository<Equipment, Integer>{
Equipment findById(int id);
}
Service
#Service
public class EquipmentServiceImpl implements EquipmentService {
#Autowired
EquipmentRepository equipmentRepository;
#Override
public Equipment findById(int id) {
return equipmentRepository.findById(id);
}
}
I wonder that why i can call a method of 'interface EquipmentRepository'. EquipmentRepository is a interface, Right ?
Spring Repository is responsible for importing the DAO's into the DI container and also it makes the unchecked exceptions into Spring DataAccessException. The Spring Repository annotation is meta annotated with the #Component annotation so that the repository classes will be taken up for component scanning.
Teams implementing traditional Java EE patterns such as "Data Access
Object" may also apply this stereotype to DAO classes, though care
should be taken to understand the distinction between Data Access
Object and DDD-style repositories before doing so. This annotation is
a general-purpose stereotype and individual teams may narrow their
semantics and use as appropriate.
A class thus annotated is eligible for Spring DataAccessException
translation when used in conjunction with a
PersistenceExceptionTranslationPostProcessor. The annotated class is
also clarified as to its role in the overall application architecture
for the purpose of tooling, aspects, etc.
Source: JavaDoc
but in your case you are also extending the JpaRepository of Spring Data JPA. Spring Data automatically provides implementations of common CRUD operations. The JpaRepository extends the interface CrudRepository which has the methods declared for all basic crud operations.
public interface EquipmentRepository extends JpaRepository<Account, Long> { … }
Defining this interface serves two purposes:
First, by extending JpaRepository we get a bunch of generic CRUD
methods into our type that allows saving Equipments, deleting them and
so on.
Second, this will allow the Spring Data JPA repository infrastructure
to scan the classpath for this interface and create a Spring bean for
it.
The #EnableJpaRepositories scans all packages below com.acme.repositories for interfaces extending JpaRepository and creates a Spring bean for it that is backed by an implementation of SimpleJpaRepository (spring data provides default imlpementations of CRUD repository through this class).
So that is why even when you haven't defined the method , you are able to do crud operations through this setup.
Refer : https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.repositories

Create new Entity Object in Spring Boot

I'm hoping someone could shed some more light on my confusion with JPA entities in a Spring Boot project. I've heard that one should never call new in a Spring project. I understand that this is to allow Spring to manage all of the beans, and getting a bean can be done through injection or through the application context explicitly.
However, it's not clear to me how to get a new JPA Entity. If I have a class annotated with #Entity and a repository class that handles my data access, how do I obtain a new entity object in my service layer?
I've included #EntityScan in my application's main class so I would assume that Spring is aware of the entity. But when I try to get it through the ApplicationContext an exception is raised. This makes sense because I don't believe the #Entity annotated classes are Spring Beans, and I don't think it would be correct to also annotate it with #Component. Any clarification would be greatly appreciated.
I'm currently using the new keyword and creating the entity objects myself in the service layer. A very simple example is below:
entities/User.java
#Entity
#Table(name = "users")
public class User {
#Id
private Long id;
private String username;
// Getters & Setters ...
}
repositories/UserRepository.java
#Repository
public interface UserRepository extends CrudRepository<User, Long> {
User findByUsername(String username);
}
services/UserServiceImpl.java
#Service
public class UserServiceImpl implements UserService {
UserRepository userRepository;
#Autowired
public UserServiceImpl(UserRepository userRepository) {
this.userRepository = userRepository;
}
public void createAndSaveUser(String username) {
User user = new User();
user.setUsername(username);
userRepository.save(user);
}
}
And we could assume that there was some other controller classes that would utilize the service layer.
In this example I am explicitly calling the new keyword in the service class method createAndSaveUser. Is this the correct way to do it or should I be getting some prototype bean from Spring that maps to my JPA entity?
In spring you can autowire/inject your beans, components or services. However the entity should not be autowired since these interactions are done through your repository. Your repository can be autowired.
When you want to create a new instance of your entity you are allowed to call new, because this does not need to be managed by spring. You can simply use the autowired repository to save it in the database. This also works the other way around because obviously you would need the autowired repository to retrieve your entity.
So yes, your method is correct.
I hope this makes it clearer for you, if you have any questions feel free to ask :)
Whatever you are doing is completely valid in spring. In example you have provided above I could figure out that you want your entity class object itself to store the values. Its absolutely correct.
You have to use new keyword to achieve that.
If you still wish to not create a new object for your Entity you have another option to do it through Bean/POJO/VO classes and mapping your entity object with these classes.
But Still i will tell that whatever you have done is completely fine.
Actually the object you are creating is for storing value purpose not just because you have some method is there in your class and so you are bound to create new Object to be able to call that method(As we do in normal java project).In spring that is handle by #Autowired annotation to create object.
Simple example is you will be auto-wiring your repositories in your service classes.
I hope this help.
It sounds good to me: you create your entity and then ask the repository to store it.. no problem with Spring.
have you checked this out? :
http://spring.io/guides/gs/accessing-data-jpa/
have fun

Mongodb dynamic multi tenancy with spring-data library [duplicate]

In a post last august sbzoom proposed a solution to make spring-data-mongoDB multi-tenant:
"You have to make your own RepositoryFactoryBean. Here is the example from the Spring Data MongoDB Reference Docs. You would still have to implement your own MongoTemplate and delay or remove the ensureIndexes() call. But you would have to rewrite a few classes to make sure your MongoTemplate is called instead of Spring's."
Did anybody implement this or something equivalent?
There's quite a few ways to skin the cat here. It essentially all boils down to on which level you'd like to apply the tenancy.
Basics
The basic approach is to bind some kind of key identifying the customer on a per-thread basis, so that you can find out about the customer the current thread of execution deals with. This is usually achieved by populating a ThreadLocal with some authentication related information as you can usually derive the tenant from the logged in user.
Now if that's in place there's a few options of where to apply the tenant knowledge. Let me briefly outline the most common ones:
Multi-tenancy on the database level
One way to separate data for multiple clients is to have individual databases per tenant. Spring Data MongoDB's core abstraction for this is the MongoDBFactory interface. The easiest way here is to override SimpleMongoDbFactory.getDb(String name) and call the parent method with the database name e.g. enriched by the tenant prefix or the like.
Multi-tenancy on the collection level
Another option is to have tenant specific collections, e.g. through tenant pre- or postfixes. This mechanism can actually be leveraged by using the Spring Expression language (SpEl) in the #Document annotation's collectionName attribute. First, expose the tenant prefix through a Spring bean:
#Component("tenantProvider")
public class TenantProvider {
public String getTenantId() {
// … implement ThreadLocal lookup here
}
}
Then use SpEL in your domain types #Document mapping:
#Document(collectionName = "#{tenantProvider.getTenantId()}_accounts"
public class Account { … }
SpEl allows you to refer to Spring beans by name and execute methods on them. MongoTemplate (and thus the repository abstraction transitively) will use the mapping metadata of the document class and the mapping subsystem will evaluate the collectionName attribute to find out about the collection to interact with.
I had a similar approach to Oliver Gierke.
At least on database-level. https://github.com/Loki-Afro/multi-tenant-spring-mongodb
You should be able to do things like this:
MultiTenantMongoDbFactory.setDatabaseNameForCurrentThread("test");
this.personRepository.save(createPerson("Phillip", "Wirth", ChronoUnit.YEARS.between(
LocalDate.of(1992, Month.FEBRUARY, 3),
LocalDate.now())));
System.out.println("data from test: " + this.personRepository.findAll());
// okay? fine. - lets switch the database
MultiTenantMongoDbFactory.setDatabaseNameForCurrentThread("test666");
// should be empty
System.out.println("data from test666: " + this.personRepository.findAll());
for springboot 2.3.3
overriding doGetMongoDatabase helped to achieve multi tenancy
protected MongoDatabase doGetMongoDatabase(String dbName) {
}
https://github.com/jose-m-thomas/mongo_multi_tenancy_spring_boot_2_3_3
Full featured multi-tenant/tenancy with Spring Boot + MongoDB + Spring MVC with shared/global database configuration.
https://github.com/arun2pratap/multitenant-spring-mongodb

auto-mapping CrudRepository with default rest uri endpoints in spring

I'm about to create a stock-standard rest CRUD api and have taken note of the handy CrudRepository class given in the spring-data framework. I'm planning on also using spring to declare #RequestMappings to hook up the default crud operations to their URL counterparts (e.g. /customer/{id} --> CrudRepository.findOne({id}), etc).
Is there a spring utility class to acheive this or will i need to roll my own?
Ah ha! What I'm looking for is a org.springframework.data.rest.core.annotation.RepositoryRestResource located in the spring data rest webmvc project. maven co-ordinates: "org.springframework.data:spring-data-rest-webmvc"
an example extract from the documentation:
#RepositoryRestResource(collectionResourceRel = "people", path = "people")
public interface PersonRepository extends PagingAndSortingRepository<Person, Long> {
List<Person> findByLastName(#Param("name") String name);
}
enter code here
This repository is an interface and will allow you to perform various operations involving Person objects. It gets these operations by > extending the PagingAndSortingRepositry interface defined in Spring Data Commons.
At runtime, Spring Data REST will create an implementation of this interface automatically. Then it will use the #RepositoryRestResource > annotation to direct Spring MVC to create RESTful endpoints at /people.

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