This chapter includes details of the JPA repository implementation.

The JPA module of Spring Data contains a custom namespace that allows defining repository beans. It also contains certain features and element attributes that are special to JPA. Generally the JPA repositories can be set up using the repositories element: <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:jpa="http://www.springframework.org/schema/data/jpa" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa.xsd"> <jpa:repositories base-package="com.acme.repositories" /> </beans> Using this element looks up Spring Data repositories as described in . Beyond that it activates persistence exception translation for all beans annotated with @Repository to let exceptions being thrown by the JPA presistence providers be converted into Spring's DataAccessException hierarchy. Beyond the default attributes of the repositories element the JPA namespace offers additional attributes to gain more detailled control over the setup of the repositories: entity-manager-factory-ref Explicitly wire the EntityManagerFactory to be used with the repositories being detected by the repositories element. Usually used if multiple EntityManagerFactory beans are used within the application. If not configured we will automatically lookup the single EntityManagerFactory configured in the ApplicationContext. transaction-manager-ref Explicitly wire the PlatformTransactionManager to be used with the repositories being detected by the repositories element. Usually only necessary if multiple transaction managers and/or EntityManagerFactory beans have been configured. Default to a single defined PlatformTransactionManager inside the current ApplicationContext.

The JPA module supports defining a query manually as String or have it being derived from the method name. Although getting a query derived from the method name is quite convenient, one might face the situation in which either the method name parser does not support the keyword one wants to use or the method name would get unnecessarily ugly. So you can either use JPA named queries through a naming convention (see for more information) or rather annotate your query method with @Query (see for details).

Generally the query creation mechanism for JPA works as described in . Here's a short example of what a JPA query method translates into: public interface UserRepository extends Repository<User, Long> { List<User> findByEmailAddressAndLastname(String emailAddress, String lastname); }We will create a query using the JPA criteria API from this but essentially this translates into the following query: select u from User u where u.emailAddress = ?1 and u.lastname = ?2 Spring Data JPA will do a property check and traverse nested properties as described in . Here's an overview of the keywords supported for JPA and what a method containing that keyword essentially translates to. Keyword Sample JPQL snippet And findByLastnameAndFirstname … where x.lastname = ?1 and x.firstname = ?2 Or findByLastnameOrFirstname … where x.lastname = ?1 or x.firstname = ?2 Between findByStartDateBetween … where x.startDate between 1? and ?2 LessThan findByAgeLessThan … where x.age < ?1 GreaterThan findByAgeGreaterThan … where x.age > ?1 After findByStartDateAfter … where x.startDate > ?1 Before findByStartDateBefore … where x.startDate < ?1 IsNull findByAgeIsNull … where x.age is null IsNotNull,NotNull findByAge(Is)NotNull … where x.age not null Like findByFirstnameLike … where x.firstname like ?1 NotLike findByFirstnameNotLike … where x.firstname not like ?1 StartingWith findByFirstnameStartingWith … where x.firstname like ?1 (parameter bound with prepended %) ngWith findByFirstnameEndingWith … where x.firstname like ?1 (parameter bound with appended %) Containing findByFirstnameContaining … where x.firstname like ?1 (parameter bound wrapped in %) OrderBy findByAgeOrderByLastnameDesc … where x.age = ?1 order by x.lastname desc Not findByLastnameNot … where x.lastname <> ?1 In findByAgeIn(Collection<Age> ages) … where x.age in ?1 NotIn findByAgeNotIn(Collection<Age> age) … where x.age not in ?1 True findByActiveTrue() … where x.active = true False findByActiveFalse() … where x.active = false In and NotIn also take any subclass of Collection as parameter as well as arrays or varargs. For other syntactical versions of the very same logical operator check .

The examples use simple <named-query /> element and @NamedQuery annotation. The queries for these configuration elements have to be defined in JPA query language. Of course you can use <named-native-query /> or @NamedNativeQuery too. These elements allow you to define the query in native SQL by losing the database platform independence. To use XML configuration simply add the necessary <named-query /> element to the orm.xml JPA configuration file located in META-INF folder of your classpath. Automatic invocation of named queries is enabled by using some defined naming convention. For more details see below. <named-query name="User.findByLastname"> <query>select u from User u where u.lastname = ?1</query> </named-query> As you can see the query has a special name which will be used to resolve it at runtime. Annotation configuration has the advantage of not needing another configuration file to be edited, probably lowering maintenance costs. You pay for that benefit by the need to recompile your domain class for every new query declaration. @Entity @NamedQuery(name = "User.findByEmailAddress", query = "select u from User u where u.emailAddress = ?1") public class User { } To allow execution of these named queries all you need to do is to specify the UserRepository as follows: public interface UserRepository extends JpaRepository<User, Long> { List<User> findByLastname(String lastname); User findByEmailAddress(String emailAddress); } Spring Data will try to resolve a call to these methods to a named query, starting with the simple name of the configured domain class, followed by the method name separated by a dot. So the example here would use the named queries defined above instead of trying to create a query from the method name.

Using named queries to declare queries for entities is a valid approach and works fine for a small number of queries. As the queries themselves are tied to the Java method that executes them you actually can bind them directly using the Spring Data JPA @Query annotation rather than annotating them to the domain class. This will free the domain class from persistence specific information and co-locate the query to the repository interface. Queries annotated to the query method will take precedence over queries defined using @NamedQuery or named queries declared in orm.xml. public interface UserRepository extends JpaRepository<User, Long> { @Query("select u from User u where u.emailAddress = ?1") User findByEmailAddress(String emailAddress); } The @Query annotation allows to execute native queries by setting the nativeQuery flag to true. Note, that we currently don't support execution of pagination or dynamic sorting for native queries as we'd have to manipulate the actual query declared and we cannot do this reliably for native SQL.

By default Spring Data JPA will use position based parameter binding as described in all the samples above. This makes query methods a little error prone to refactoring regarding the parameter position. To solve this issue you can use @Param annotation to give a method parameter a concrete name and bind the name in the query: public interface UserRepository extends JpaRepository<User, Long> { @Query("select u from User u where u.firstname = :firstname or u.lastname = :lastname") User findByLastnameOrFirstname(@Param("lastname") String lastname, @Param("firstname") String firstname); } Note that the method parameters are switched according to the occurrence in the query defined.

All the sections above describe how to declare queries to access a given entity or collection of entities. Of course you can add custom modifying behaviour by using facilities described in . As this approach is feasible for comprehensive custom functionality, you can achieve the execution of modifying queries that actually only need parameter binding by annotating the query method with @Modifying: @Modifying @Query("update User u set u.firstname = ?1 where u.lastname = ?2") int setFixedFirstnameFor(String firstname, String lastname); This will trigger the query annotated to the method as updating query instead of a selecting one. As the EntityManager might contain outdated entities after the execution of the modifying query, we automatically clear it (see JavaDoc of EntityManager.clear() for details). This will effectively drop all non-flushed changes still pending in the EntityManager. If you don't wish the EntityManager to be cleared automatically you can set @Modifying annotation's clearAutomatically attribute to false;

To apply JPA QueryHints to the queries declared in your repository interface you can use the QueryHints annotation. It takes an array of JPA QueryHint annotations plus a boolean flag to potentially disable the hints applied to the addtional count query triggered when applying pagination. public interface UserRepository extends Repository<User, Long> { @QueryHints(value = { @QueryHint(name = "name", value = "value")}, forCounting = false) Page<User> findByLastname(String lastname, Pageable pageable); } The just shown declaration would apply the configured QueryHint for that actually query but omit applying it to the count query triggered to calculate the total number of pages.

JPA 2 introduces a criteria API that can be used to build queries programmatically. Writing a criteria you actually define the where-clause of a query for a domain class. Taking another step back these criteria can be regarded as predicate over the entity that is described by the JPA criteria API constraints. Spring Data JPA takes the concept of a specification from Eric Evans' book "Domain Driven Design", following the same semantics and providing an API to define such Specifications using the JPA criteria API. To support specifications you can extend your repository interface with the JpaSpecificationExecutor interface: public interface CustomerRepository extends CrudRepository<Customer, Long>, JpaSpecificationExecutor { … } The additional interface carries methods that allow you to execute Specifications in a variety of ways. For example, the readAll method will return all entities that match the specification: List<T> readAll(Specification<T> spec); The Specification interface is as follows: public interface Specification<T> { Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder builder); } Okay, so what is the typical use case? Specifications can easily be used to build an extensible set of predicates on top of an entity that then can be combined and used with JpaRepository without the need to declare a query (method) for every needed combination. Here's an example: public class CustomerSpecs { public static Specification<Customer> isLongTermCustomer() { return new Specification<Customer>() { Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder builder) { LocalDate date = new LocalDate().minusYears(2); return builder.lessThan(root.get(Customer_.createdAt), date); } }; } public static Specification<Customer> hasSalesOfMoreThan(MontaryAmount value) { return new Specification<Customer>() { Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder builder) { // build query here } }; } } Admittedly the amount of boilerplate leaves room for improvement (that will hopefully be reduced by Java 8 closures) but the client side becomes much nicer as you will see below. Besides that we have expressed some criteria on a business requirement abstraction level and created executable Specifications. So a client might use a Specification as follows: List<Customer> customers = customerRepository.findAll(isLongTermCustomer()); Okay, why not simply create a query for this kind of data access? You're right. Using a single Specification does not gain a lot of benefit over a plain query declaration. The power of Specifications really shines when you combine them to create new Specification objects. You can achieve this through the Specifications helper class we provide to build expressions like this: MonetaryAmount amount = new MonetaryAmount(200.0, Currencies.DOLLAR); List<Customer> customers = customerRepository.readAll( where(isLongTermCustomer()).or(hasSalesOfMoreThan(amount)));As you can see, Specifications offers some glue-code methods to chain and combine Specifications. Thus extending your data access layer is just a matter of creating new Specification implementations and combining them with ones already existing.

CRUD methods on repository instances are transactional by default. For reading operations the transaction configuration readOnly flag is set to true, all others are configured with a plain @Transactional so that default transaction configuration applies. For details see JavaDoc of Repository. If you need to tweak transaction configuration for one of the methods declared in Repository simply redeclare the method in your repository interface as follows: public interface UserRepository extends JpaRepository<User, Long> { @Override @Transactional(timeout = 10) public List<User> findAll(); // Further query method declarations } This will cause the findAll() method to be executed with a timeout of 10 seconds and without the readOnly flag. Another possibility to alter transactional behaviour is using a facade or service implementation that typically covers more than one repository. Its purpose is to define transactional boundaries for non-CRUD operations: @Service class UserManagementImpl implements UserManagement { private final UserRepository userRepository; private final RoleRepository roleRepository; @Autowired public UserManagementImpl(UserRepository userRepository, RoleRepository roleRepository) { this.userRepository = userRepository; this.roleRepository = roleRepository; } @Transactional public void addRoleToAllUsers(String roleName) { Role role = roleRepository.findByName(roleName); for (User user : userRepository.readAll()) { user.addRole(role); userRepository.save(user); } } This will cause call to addRoleToAllUsers(…) to run inside a transaction (participating in an existing one or create a new one if none already running). The transaction configuration at the repositories will be neglected then as the outer transaction configuration determines the actual one used. Note that you will have to activate <tx:annotation-driven /> explicitly to get annotation based configuration at facades working. The example above assumes you are using component scanning.

To allow your query methods to be transactional simply use @Transactional at the repository interface you define. @Transactional(readOnly = true) public interface UserRepository extends JpaRepository<User, Long> { List<User> findByLastname(String lastname); @Modifying @Transactional @Query("delete from User u where u.active = false") void deleteInactiveUsers(); } Typically you will want the readOnly flag set to true as most of the query methods will only read data. In contrast to that deleteInactiveUsers() makes use of the @Modifying annotation and overrides the transaction configuration. Thus the method will be executed with readOnly flag set to false. It's definitely reasonable to use transactions for read only queries and we can mark them as such by setting the readOnly flag. This will not, however, act as check that you do not trigger a manipulating query (although some databases reject INSERT and UPDATE statements inside a read only transaction). The readOnly flag instead is propagated as hint to the underlying JDBC driver for performance optimizations. Furthermore, Spring will perform some optimizations on the underlying JPA provider. E.g. when used with Hibernate the flush mode is set to NEVER when you configure a transaction as readOnly which causes Hibernate to skip dirty checks (a noticeable improvement on large object trees).

To specify the lock mode to be used the @Lock annotation can be used on query methods: interface UserRepository extends Repository<User, Long> { // Plain query method @Lock(LockModeType.READ) List<User> findByLastname(String lastname); } This method declaration will cause the query being triggered to be equipped with the LockModeType READ. You can also define locking for CRUD methods by redeclaring them in your repository interface and adding the @Lock annotation: interface UserRepository extends Repository<User, Long> { // Redeclaration of a CRUD method @Lock(LockModeType.READ); List<User> findAll(); }

Most applications will require some form of auditability to track when an entity was created or modified and by whom. Spring Data JPA provides facilities to add this audit information to an entity transparently by AOP means. To take part in this functionality your domain classes must implement a more advanced interface: public interface Auditable<U, ID extends Serializable> extends Persistable<ID> { U getCreatedBy(); void setCreatedBy(U createdBy); DateTime getCreatedDate(); void setCreated(Date creationDate); U getLastModifiedBy(); void setLastModifiedBy(U lastModifiedBy); DateTime getLastModifiedDate(); void setLastModified(Date lastModifiedDate); } As you can see the modifying entity itself only has to be an entity. Mostly this will be some sort of User entity, so we chose U as parameter type. To minimize boilerplate code Spring Data JPA offers AbstractPersistable and AbstractAuditable base classes that implement and pre-configure entities. Thus you can decide to only implement the interface or enjoy more sophisticated support by extending the base class. Spring Data JPA ships with an entity listener that can be used to trigger capturing auditing information. So first you have to register the AuditingEntityListener inside your orm.xml to be used for all entities in your persistence contexts: <persistence-unit-metadata> <persistence-unit-defaults> <entity-listeners> <entity-listener class="….data.jpa.domain.support.AuditingEntityListener" /> </entity-listeners> </persistence-unit-defaults> </persistence-unit-metadata> Now activating auditing functionality is just a matter of adding the Spring Data JPA auditing namespace element to your configuration: <jpa:auditing auditor-aware-ref="yourAuditorAwareBean" /> As you can see you have to provide a bean that implements the AuditorAware interface which looks as follows: public interface AuditorAware<T, ID extends Serializable> { T getCurrentAuditor(); } Usually you will have some kind of authentication component in your application that tracks the user currently working with the system. This component should be AuditorAware and thus allow seamless tracking of the auditor.

Spring supports having multiple persistence units out of the box. Sometimes, however, you might want to modularize your application but still make sure that all these modules run inside a single persistence unit at runtime. To do so Spring Data JPA offers a PersistenceUnitManager implementation that automatically merges persistence units based on their name. <bean class="….LocalContainerEntityManagerFactoryBean"> <property name="persistenceUnitManager"> <bean class="….MergingPersistenceUnitManager" /> </property </bean>

A plain JPA setup requires all annotation mapped entity classes listed in orm.xml. Same applies to XML mapping files. Spring Data JPA provides a ClasspathScanningPersistenceUnitPostProcessor that gets a base package configured and optionally takes a mapping filename pattern. It will then scan the given package for classes annotated with @Entity or @MappedSuperclass and also loads the configuration files matching the filename pattern and hands them to the JPA configuration. The PostProcessor has to be configured like this <bean class="….LocalContainerEntityManagerFactoryBean"> <property name="persistenceUnitPostProcessors"> <list> <bean class="org.springframework.data.jpa.support.ClasspathScanningPersistenceUnitPostProcessor"> <constructor-arg value="com.acme.domain" /> <property name="mappingFileNamePattern" value="**/*Mapping.xml" /> </bean> </list> </property> </bean> As of Spring 3.1 a package to scan can be configured on the LocalContainerEntityManagerFactoryBean directly to enable classpath scanning for entity classes. See the JavaDoc for details.

Instances of the repository interfaces are usually created by a container, which Spring is the most natural choice when working with Spring Data. There's sophisticated support to easily set up Spring to create bean instances documented in . As of version 1.1.0 Spring Data JPA ships with a custom CDI extension that allows using the repository abstraction in CDI environments. The extension is part of the JAR so all you need to do to activate it is dropping the Spring Data JPA JAR into your classpath. You can now set up the infrastructure by implementing a CDI Producer for the EntityManagerFactory: class EntityManagerFactoryProducer { @Produces @ApplicationScoped public EntityManagerFactory createEntityManagerFactory() { return Persistence.createEntityManagerFactory("my-presistence-unit"); } public void close(@Disposes EntityManagerFactory entityManagerFactory) { entityManagerFactory.close(); } } The Spring Data JPA CDI extension will pick up all EntityManagers availables as CDI beans and create a proxy for a Spring Data repository whenever an bean of a repository type is requested by the container. Thus obtaining an instance of a Spring Data repository is a matter of declaring an @Injected property: class RepositoryClient { @Inject PersonRepository repository; public void businessMethod() { List<Person> people = repository.findAll(); } }