#Repository
public interface userRepository extends JpaRepository<User, Long> {
}
There are many sites showing this way of creating DAO in Spring 4 using JpaRepository. #Repository also creating instance just like #Component, #Service etc. Container internally beans by using new operator while component scan (using #Component scan annotation) of classes having annotation #Component, #Service etc. Then how container create instance for #Repository as shown above, as it is an interface which is purely abstract and we can't create instance for interface using new operator.
Spring will create a SimpleJpaRepository instance for declared Interfaces that extend JpaRepository.
Note: there is much more magic going on. You can add your own queries via #Query to the interface and Repositories also support transaction management. To achieve that the Repository will be wrapped in a proxy which can intercept and dynamically implement its methods.
Related
Can we use #Repository for DAO layer in spring boot ?
What is the difference between #Component and #Repository ?
Which one should we use for DAO layer in Spring boot ?
#Repository is a specialization of #Component whose purpose is to handle DAO. So the answer is yes.
#Repository javadoc states :
Indicates that an annotated class is a "Repository", originally defined by Domain-Driven Design (Evans, 2003) as "a mechanism for encapsulating storage, retrieval, and search behavior which emulates a collection of objects".
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.
#Repository is an annotation marker. No difference between #Component and #Repository, spring already can create bean instance from your interface if you extends JpaRepository or other spring repository interfaces
For example:
public interface UserRepository extends JpaRepository<User, BigInteger> {
User findByUsernameOrEmail(String username, String email);
}
For more information please follow the link
I'm using Spring Data JPA repositories (like MyRepo extends JpaRepository) and it works without #Repository and without #EnableJpaRepositories annotations. Could someone explain why?
Probably you are using Spring Boot.
Spring Data repositories usually extend from the Repository or CrudRepository interfaces. If you use auto-configuration, repositories are searched from the package containing your main configuration class (the one annotated with #EnableAutoConfiguration or #SpringBootApplication) down.
Please check the Spring Boot Reference Documentation (v2.7.2) for more details.
you don't need #Repository to make use of Spring Data JPA.
The Interface extending the CrudRepository or JPARepository would work even without annotating it with #Repository.
The Core reason why you need to have this annotation in place is it makes unchecked exceptions thrown in the DAO layer eligible to be translated into Spring DataAccessException. Which in turn would be easier to work with. This is the important aspect of using #Repository
More details see this -> https://www.youtube.com/watch?v=z2re1MfWtz0&list=PLO0KWyajXMh4fGMvAw1yQ1x7mWayRcmX3&index=8&t=0s
For more information look into these class which is used to auto-configure Spring Data JPA Repositories:
JpaRepositoriesAutoConfigureRegistrar
Docs : http://www.atetric.com/atetric/javadoc/org.springframework.boot/spring-boot-autoconfigure/1.2.0.RELEASE/org/springframework/boot/autoconfigure/data/jpa/JpaRepositoriesAutoConfigureRegistrar.html
#EnableJpaRepositories
private static class EnableJpaRepositoriesConfiguration {
}
I am using spring data JPA repository, my requirement is when i call repository class methods in service class it should show only custom methods like addUser(X,Y) instead of save().
Few things i understand, implementation of spring repository is provided by spring framework at runtime, So we cannot provide out own implementation. (This will overhead).
All methods in JPARepository is public only, so its obivious when we implement this interface all methods will be visible through out.
I am thinking of using DAO and Repository both at same time. DAO will provide custom function signature and repository will implement DAO interface.
Any Hack ?
If you don't want the methods from JpaRepository or CrudRepository, don't extend those but just Repository instead. It is perfectly fine to have a repository interface like
MyVeryLimitedRepository extends Repository<User, Long> {
User findByName(String name);
}
Of course methods like addUser(X,Y) will need a custom implementation.
You can very well use DAO pattern in this case .
By implementing DAO Pattern in Service Class
You create a wrapper between Service and Repository.
You can custom code your DAO layer to only expose custom methods to service layer
Background
I'm trying to create a custom implementation for my spring boot data jpa application.
I've created a UserRepsitoryCustom interface with "List<User> getUsers(String type)" method.
I've created a UserRepository interface with extends CrudRepository<User, Long>, QueryDslPredicateExecutor<User>, UserRepositoryCustom.
I've created a UserRepositoryImpl class which extends UserRepositoryCustom interface and implements the "getUsers(String type)" method.
Problem
My expectation was that spring boot-data-jpa will create me a repository bean that combines all the goodies from CrudRepository & QueryDslPredicateExecutor and additional will know to use my custom implementation repository.
Currently, all I'm getting is
PropertyReferenceException: No property getUsers found...
I haven't annotated the UserRepositoryImpl with any #Component or #Repository. and I haven't changed any default configuration.
What am I doing wrong?
Thanks!
I've found my problem!!! The UserRepositoryImpl was in the wrong package name... I've moved it to the right package name and it's done!
I have a question about spring + hibernate
I always use hibernate for my develeppoment, I generate images of the tables and the class DAO
then at logic metier I make simple calls to these methods dao ....
for exemple UserDao=new UserDao () then userdao.persist() ...
Now I have intgret spring, and I do not yet understand ..
1
what is the plus made by him knowing that he is also making calls
has dao Service (the writings that manually) it does not generate the
class dao with hibernate
2
is that with spring I would not worry about manage session for
example open session, close session commit() ...
thank you in advance I would like to have an idea Ccool:
At its core, Spring is a dependency injection framework. This means that instead of doing
public class MyService
private MyDao dao;
public MyService() {
dao = new MyDao();
}
}
You can do
public class MyService
private MyDao dao;
#Autowired
public MyService(MyDao dao) {
this.dao = dao;
}
}
And Spring will automatically call the constructor and inject an instance of MyDao. The main benefit is that the code is easily unit-testable.
On top of that, it allows injecting proxies instead of the actual implementations directly. These proxies will indeed handle the transaction management for you, and more (exception translation, security checks, etc.).
So instead of explicitely opening, committing and rollbacking transactions, you would simply annotate a service method with #Transactional, and Spring would open, commit/rollback the transaction. And the transaction context would automatically propagate to the nested service calls.
This short answer is only to give you an idea. To learn more, read about dependency injection, and read the Spring documentation.
Use Spring annotations like #Service for service classes, #Repository for Dao classes and #Controller for action controllers. Use of #Transactional on service class or methods is suffice to carry out transactions.