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:
Example 2.1. Setting up JPA repositories using the namespace
<?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 Section 1.2.3, “Creating repository instances”. Beyond that it activates persistence exception translation for all beans annotated with @Repository
to let exceptions being thrown by the JPA persistence 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 detailed control over the setup of the repositories:
Table 2.1. Custom JPA-specific attributes of the repositories element
| Explicitly wire the |
| Explicitly wire the |
Note that we require a PlatformTransactionManager
bean named transactionManager
to be present if no explicit transaction-manager-ref
is defined.
The Spring Data JPA repositories support cannot only be activated through an XML namespace but also using an annotation through JavaConfig.
Example 2.2. Spring Data JPA repositories using JavaConfig
@Configuration @EnableJpaRepositories @EnableTransactionManagement class ApplicationConfig { @Bean public DataSource dataSource() { EmbeddedDatabaseBuilder builder = new EmbeddedDatabaseBuilder(); return builder.setType(EmbeddedDatabaseType.HSQL).build(); } @Bean public EntityManagerFactory entityManagerFactory() { HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter(); vendorAdapter.setGenerateDdl(true); LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean(); factory.setJpaVendorAdapter(vendorAdapter); factory.setPackagesToScan("com.acme.domain"); factory.setDataSource(dataSource()); factory.afterPropertiesSet(); return factory.getObject(); } @Bean public PlatformTransactionManager transactionManager() { JpaTransactionManager txManager = new JpaTransactionManager(); txManager.setEntityManagerFactory(entityManagerFactory()); return txManager; } }
The just shown configuration class sets up an embedded HSQL database using the EmbeddedDatabaseBuilder
API of spring-jdbc. We then set up a EntityManagerFactory
and use Hibernate as sample persistence provider. The last infrastructure component declared here is the JpaTransactionManager
. We finally activate Spring Data JPA repositories using the @EnableJpaRepositories
annotation which essentially carries the same attributes as the XML namespace does. If no base package is configured it will use the one the configuration class resides in.
Saving an entity can be performed via the CrudRepository.save(…)
-Method. It will persist or merge the given entity using the underlying JPA EntityManager
. If the entity has not been persisted yet Spring Data JPA will save the entity via a call to the entityManager.persist(…)
method, otherwise the entityManager.merge(…)
method will be called.
Spring Data JPA offers the following strategies to detect whether an entity is new or not:
Table 2.2. Options for detection whether an entity is new in Spring Data JPA
Id-Property inspection (default) | By default Spring Data JPA inspects the identifier property of the given entity. If the identifier property is |
Implementing | If an entity implements |
Implementing | You can customize the |
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 Section 2.3.3, “Using JPA NamedQueries” for more information) or rather annotate your query method with @Query (see Section 2.3.4, “Using @Query” for details).
Generally the query creation mechanism for JPA works as described in Section 1.2, “Query methods”. Here’s a short example of what a JPA query method translates into:
Example 2.3. Query creation from method names
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.
Table 2.3. Supported keywords inside method names
Keyword | Sample | JPQL snippet |
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The examples use simple |
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.
Example 2.4. XML named query configuration
<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.
Example 2.5. Annotation based named query configuration
@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:
Example 2.6. Query method declaration in UserRepository
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
.
Example 2.7. Declare query at the query method using @Query
public interface UserRepository extends JpaRepository<User, Long> { @Query("select u from User u where u.emailAddress = ?1") User findByEmailAddress(String emailAddress); }
Using advanced LIKE
expressionsThe query execution mechanism for manually defined queries using @Query allow the definition of advanced LIKE
expressions inside the query definition.
Example 2.8. Advanced LIKE
expressions in @Query
public interface UserRepository extends JpaRepository<User, Long> { @Query("select u from User u where u.firstname like %?1") List<User> findByFirstnameEndsWith(String firstname); }
In the just shown sample LIKE
delimiter character %
is recognized and the query transformed into a valid JPQL query (removing the %
). Upon query execution the parameter handed into the method call gets augmented with the previously recognized LIKE
pattern.
Native queriesThe @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.
Example 2.9. Declare a native query at the query method using @Query
public interface UserRepository extends JpaRepository<User, Long> { @Query(value = "SELECT * FROM USERS WHERE EMAIL`ADDRESS = ?0", nativeQuery = true) User findByEmailAddress(String emailAddress); }
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.
Example 2.10. Using named parameters
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.
As of Spring Data JPA release 1.4 we support the usage of restricted SpEL template expressions in manually defined queries via @Query
. Upon query execution these expressions are evaluated against a predefined set of variables. We support the following list of variables to be used in a manual query.
Table 2.4. Supported variables inside SpEL based query templates
Variable | Usage |
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Description |
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The following example demonstrates one use case for the #{#entityName}
expression in a query string where you want to define a repository interface with a query method with a manually defined query. In order not to have to state the actual entity name in the query string of a @Query
annotation one can use the #{#entityName}
Variable.
Note | |
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The |
Example 2.11. Using SpEL expressions in repository query methods - entityName
@Entity public class User { @Id @GeneratedValue Long id; String lastname; } public interface UserRepository extends JpaRepository<User,Long> { @Query("select u from #{#entityName} u where u.lastname = ?1") List<User> findByLastname(String lastname); }
Of course you could have just used User in the query declaration directly but that would require you to change the query as well. The reference to #entityName
will pick up potential future remappings of the User class to a different entity name (e.g. by using @Entity(name = "MyUser")
.
Another use case for the #{#entityName}
expression in a query string is if you want to define a generic repository interface with specialized repository interfaces for a concrete domain type. In order not to have to repeat the definition of custom query methods on the concrete interfaces you can use the entity name expression in the query string of the @Query
annotation in the generic repository interface.
Example 2.12. Using SpEL expressions in repository query methods - entityName with inheritance
@MappedSuperclass public abstract class AbstractMappedType { … String attribute } @Entity public class ConcreteType extends AbstractMappedType { … } @NoRepositoryBean public interface MappedTypeRepository<T extends AbstractMappedType> extends Repository<T, Long> { @Query("select t from #{#entityName} t where t.attribute = ?1") List<T> findAllByAttribute(String attribute); } public interface ConcreteRepository extends MappedTypeRepository<ConcreteType> { … }
In the example the interface MappedTypeRepository
is the common parent interface for a few domain types extending AbstractMappedType
. It also defines the generic method findAllByAttribute(…)
which can be used on instances of the specialized repository interfaces. If you now invoke findByAllAttribute(…)
on ConcreteRepository
the query being executed will be select t from ConcreteType t where t.attribute = ?1
.
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 Section 1.3, “Custom implementations for Spring Data repositories”. 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
:
Example 2.13. Declaring manipulating queries
@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 do not automatically clear it (see JavaDoc of EntityManager.clear()
for details) since this will effectively drop all non-flushed changes still pending in the EntityManager
. If you wish the EntityManager
to be cleared automatically you can set @Modifying
annotation’s clearAutomatically
attribute to true
.
To apply JPA query hints 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.
Example 2.14. Using QueryHints with a repository method
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.
The JPA 2.1 specification introduced support for specifiying Fetch- and LoadGraphs that we also support via the @EntityGraph
annotation which allows to reference a @NamedEntityGraph
definition, that can be annotated on an entity, to be used to configure the fetch plan of the resulting query. The type (Fetch / Load) of the fetching can be configured via the type
attribute on the @EntityGraph
annotation. Please have a look at the JPA 2.1 Spec 3.7.4 for further reference.
Example 2.15. Defining a named entity graph on an entity.
@Entity @NamedEntityGraph(name = "GroupInfo.detail", attributeNodes = @NamedAttributeNode("members")) public class GroupInfo { // default fetch mode is lazy. @ManyToMany List<GroupMember> members = new ArrayList<GroupMember>(); … }
Example 2.16. Referencing a named entity graph definition on an repository query method.
@Repository public interface GroupRepository extends CrudRepository<GroupInfo, String> { @EntityGraph(value = "GroupInfo.detail", type = EntityGraphType.LOAD) GroupInfo getByGroupName(String name); }
The JPA 2.1 specification introduced support for calling stored procedures via the JPA criteria query API. We Introduced the @Procedure
annotation for declaring stored procedure metadata on a repository method.
Example 2.17. The definition of the pus1inout procedure in HSQL DB.
/; DROP procedure IF EXISTS plus1inout /; CREATE procedure plus1inout (IN arg int, OUT res int) BEGIN ATOMIC set res = arg ` 1; END /;
Metadata for stored procedures can be configured via the NamedStoredProcedureQuery
annotation on an entity type.
@Entity @NamedStoredProcedureQuery(name = "User.plus1", procedureName = "plus1inout", parameters = { @StoredProcedureParameter(mode = ParameterMode.IN, name = "arg", type = Integer.class), @StoredProcedureParameter(mode = ParameterMode.OUT, name = "res", type = Integer.class) }) public class User {}
Stored procedures can be referenced from a repository method in multiple ways. The stored procedure to be called can either be defined directly via the value
or procedureName
attribute of the @Procedure
annotation or indirectly via the name
attribute. If no name is configured the name of the repository method is used as a fallback.
Example 2.18. Referencing explicitly mapped procedure with name "plus1inout" in database.
@Procedure("plus1inout")
Integer explicitlyNamedPlus1inout(Integer arg);
Example 2.19. Referencing implicitly mapped procedure with name "plus1inout" in database via procedureName
alias.
@Procedure(procedureName = "plus1inout")
Integer plus1inout(Integer arg);
Example 2.20. Referencing explicitly mapped named stored procedure "User.plus1IO" in EntityManager.
@Procedure(name = "User.plus1IO") Integer entityAnnotatedCustomNamedProcedurePlus1IO(@Param("arg") Integer arg);
Example 2.21. Referencing implicitly mapped named stored procedure "User.plus1" in EntityManager via method-name.
@Procedure Integer plus1(@Param("arg") Integer arg);
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 findAll
method will return all entities that match the specification:
List<T> findAll(Specification<T> spec);
The Specification
interface is defined 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:
Example 2.22. Specifications for a Customer
public class CustomerSpecs { public static Specification<Customer> isLongTermCustomer() { return new Specification<Customer>() { public Predicate toPredicate(Root<Customer> 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>() { public 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. The _Customer
type is a metamodel type generated using the JPA Metamodel generator (see the Hibernate implementation’s documentation for example). So the expression _Customer.createdAt
is asuming the Customer
having a createdAt
attribute of type Date
. 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:
Example 2.23. Using a simple Specification
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:
Example 2.24. Combined Specifications
MonetaryAmount amount = new MonetaryAmount(200.0, Currencies.DOLLAR); List<Customer> customers = customerRepository.findAll( where(isLongTermCustomer()).or(hasSalesOfMoreThan(amount)));
As you can see, Specifications
offers some glue-code methods to chain and combine Specification
instances. 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 CrudRepository
. If you need to tweak transaction configuration for one of the methods declared in a repository simply redeclare the method in your repository interface as follows:
Example 2.25. Custom transaction configuration for CRUD
public interface UserRepository extends CrudRepository<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:
Example 2.26. Using a facade to define transactions for multiple repository calls
@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.findAll()) { 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 />
or use @EnableTransactionManagement
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.
Example 2.27. Using @Transactional at query methods
@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
.
Note | |
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It’s definitely reasonable to use transactions for read only queries and we can mark them as such by setting the |
To specify the lock mode to be used the @Lock
annotation can be used on query methods:
Example 2.28. Defining lock metadata 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:
Example 2.29. Defining lock metadata on CRUD methods
interface UserRepository extends Repository<User, Long> { // Redeclaration of a CRUD method @Lock(LockModeType.READ); List<User> findAll(); }