This chapter includes details of the JPA repository implementation.

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 as for details). This strategy tries to find a declared query that can either be defined using JPA @NamedQuery means or Hades @Query annotation (see and for details). If no declared query is found execution of the query will fail. This strategy is actually a combination of the both mentioned above. It will try to lookup a declared query first but create a custom method name based query if no named query was found. This is default lookup strategy and thus will be used if you don't configure anything explicitly. It allows quick query definition by method names but also custom tuning of these queries by introducing declared queries for those who need explicit tuning.

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 like 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 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 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 In and NotIn also take any subclass of Collection as parameter as well as arrays or varargs.

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 not to need another config file to be edited, probably lowering maintenance cost. 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 this named query 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); } Declaring this method we will try to resolve a call to this method 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 amount of queries. As the queries themselves are tied to a Java method to execute them you actually can bind them to the query executing methods using Spring Data JPA @Query annotation rather than annotating them to the domain class. This will free the domain class from persistence specific information and colocate the query to the repository interface. Querys annotated to the query method will trump queries defined using @NamedQuery or named queries declared in in orm.xml. public interface UserRepository extends JpaRepository<User, Long> { @Query("select u from User u where u.emailAddress = ?1") User findByEmailAddress(String emailAddress); }

By default Sprign Data JPA will use position based parameter binding as described in all the samples above. This makes query methods a little error prone to refactorings 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 before described how to declare queries to access a given entity or collection of entitites. 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;

JPA 2 introduces a criteria API that can be used to build queries programatically. Writing a criteria you actually define the where-clause of a query for a query of the handled domain class. Taking another step back these criterias can be regarded as predicate over the entity that is verbalized by the JPA criteria API constraints. Spring Data JPA now takes the concept of a specification from Eric Evans' book Domain Driven Design, that carries the same semantics and provides an API to define such Specifications using the JPA criteria API. Thus, there is a JpaSpecificationExecutor interface you can additionally extend with your repository interface: public interface CustomerRepository extends CrudRepository<Customer, Long>, JpaSpecificationExecutor { … } The additional interface carries methods like this one, which allow you to execute Specifications in a variety of ways. List<T> readAll(Specification<T> spec); The Specification interface now looks 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 of declaring a query (method) for every needed combination of those. 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 creating 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 gluecode 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're using component scanning.

To let your query methods 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 use the readOnly flag set to true as most of the query methods will be reading ones. 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 as we can mark them as such by setting the readOnly flag. This will not act as check that you do not trigger a manipulating query nevertheless (although some databases reject e.g. INSERT or UPDATE statements inside a transaction set to be read only) but gets propagated as hint to the underlying JDBC driver to do performance optimizations. Furthermore Spring will do some optimizations to the underlying JPA provider. E.g. when used with Hibernate the flush mode is set to NEVER when you configure a transaction as read only which causes Hibernate to skip dirty checks that gets quite noticeable on large object trees.

Most applications will require some auditability for entities allowing to track creation date and user and modification date and user. Spring Data JPA provides facilities to add this audition information to entity transparently by AOP means. To take part in this functionality your domain classes have to 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 preconfigure 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 functionlity 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 seemless tracking of the auditor.

Spring supports ahving multiple persistence units out of the box. But sometimes you might wanna modularize your application but make sure that all these module 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>