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Implementing a data access layer of an application has been cumbersome for quite a while. Too much boilerplate code had to be written. Domain classes were anemic and not designed in a real object oriented or domain driven manner.
Using both of these technologies makes developers life a lot easier regarding rich domain model's persistence. Nevertheless the amount of boilerplate code to implement repositories especially is still quite high. So the goal of the repository abstraction of Spring Data is to reduce the effort to implement data access layers for various persistence stores significantly.
The following chapters will introduce the core concepts and interfaces of Spring Data repositories in general for detailled information on the specific features of a particular store consult the later chapters of this document.
Note | |
---|---|
As this part of the documentation is pulled in from Spring Data Commons we have to decide for a particular module to be used as example. The configuration and code samples in this chapter are using the JPA module. Make sure you adapt e.g. the XML namespace declaration, types to be extended to the equivalents of the module you're actually using. |
The central interface in Spring Data repository abstraction is
Repository
(probably not that much of a
surprise). It is typeable to the domain class to manage as well as the id
type of the domain class. This interface mainly acts as marker interface
to capture the types to deal with and help us when discovering interfaces
that extend this one. Beyond that there's
CrudRepository
which provides some
sophisticated functionality around CRUD for the entity being
managed.
Example 1.1. CrudRepository
interface
public interface CrudRepository<T, ID extends Serializable> extends Repository<T, ID> { T save(T entity); T findOne(ID primaryKey); Iterable<T> findAll(); Long count(); void delete(T entity); boolean exists(ID primaryKey); // … more functionality omitted. }
Saves the given entity. | |
Returns the entity identified by the given id. | |
Returns all entities. | |
Returns the number of entities. | |
Deletes the given entity. | |
Returns whether an entity with the given id exists. |
Usually we will have persistence technology specific sub-interfaces to include additional technology specific methods. We will now ship implementations for a variety of Spring Data modules that implement this interface.
On top of the CrudRepository
there is
a PagingAndSortingRepository
abstraction
that adds additional methods to ease paginated access to entities:
Example 1.2. PagingAndSortingRepository
public interface PagingAndSortingRepository<T, ID extends Serializable> extends CrudRepository<T, ID> { Iterable<T> findAll(Sort sort); Page<T> findAll(Pageable pageable); }
Accessing the second page of User
by a page
size of 20 you could simply do something like this:
PagingAndSortingRepository<User, Long> repository = // … get access to a bean Page<User> users = repository.findAll(new PageRequest(1, 20);
Next to standard CRUD functionality repositories are usually queries on the underlying datastore. With Spring Data declaring those queries becomes a four-step process:
Declare an interface extending
Repository
or one of its sub-interfaces
and type it to the domain class it shall handle.
public interface PersonRepository extends Repository<User, Long> { … }
Declare query methods on the interface.
List<Person> findByLastname(String lastname);
Setup Spring to create proxy instances for those interfaces.
<?xml version="1.0" encoding="UTF-8"?> <beans:beans xmlns:beans="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="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"> <repositories base-package="com.acme.repositories" /> </beans>
Note | |
---|---|
Note that we use the JPA namespace here just by example. If
you're using the repository abstraction for any other store you need
to change this to the appropriate namespace declaration of your
store module which should be exchanging |
Get the repository instance injected and use it.
public class SomeClient { @Autowired private PersonRepository repository; public void doSomething() { List<Person> persons = repository.findByLastname("Matthews"); }
At this stage we barely scratched the surface of what's possible with the repositories but the general approach should be clear. Let's go through each of these steps and figure out details and various options that you have at each stage.
As a very first step you define a domain class specific repository
interface. It's got to extend Repository
and be typed to the domain class and an ID type. If you want to expose
CRUD methods for that domain type, extend
CrudRepository
instead of
Repository
.
Usually you will have your repository interface extend
Repository
,
CrudRepository
or
PagingAndSortingRepository
. If you
don't like extending Spring Data interfaces at all you can also
annotate your repository interface with
@RepositoryDefinition
. Extending
CrudRepository
will expose a complete
set of methods to manipulate your entities. If you would rather be
selective about the methods being exposed, simply copy the ones you
want to expose from CrudRepository
into
your domain repository.
Example 1.3. Selectively exposing CRUD methods
interface MyBaseRepository<T, ID extends Serializable> extends Repository<T, ID> { T findOne(ID id); T save(T entity); } interface UserRepository extends MyBaseRepository<User, Long> { User findByEmailAddress(EmailAddress emailAddress); }
In the first step we define a common base interface for all our
domain repositories and expose findOne(…)
as
well as save(…)
.These methods will be routed
into the base repository implementation of the store of your choice
because they are matching the method signatures in
CrudRepository
. So our
UserRepository
will now be able to save
users, find single ones by id as well as triggering a query to find
User
s by their email address.
The next thing we have to discuss is the definition of query methods. There are two main ways that the repository proxy is able to come up with the store specific query from the method name. The first option is to derive the query from the method name directly, the second is using some kind of additionally created query. What detailed options are available pretty much depends on the actual store, however, there's got to be some algorithm that decides what actual query is created.
There are three strategies available for the repository
infrastructure to resolve the query. The strategy to be used can be
configured at the namespace through the
query-lookup-strategy
attribute. However, It might be the
case that some of the strategies are not supported for specific
datastores. Here are your options:
This strategy will try to construct a store specific query from the query method's name. The general approach is to remove a given set of well-known prefixes from the method name and parse the rest of the method. Read more about query construction in Section 1.3.2.2, “Query creation”.
This strategy tries to find a declared query which will be used for execution first. The query could be defined by an annotation somewhere or declared by other means. Please consult the documentation of the specific store to find out what options are available for that store. If the repository infrastructure does not find a declared query for the method at bootstrap time it will fail.
This strategy is actually a combination of CREATE
and USE_DECLARED_QUERY
. It will try to lookup a
declared query first but create a custom method name based query if
no declared query was found. This is the 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 as needed.
The query builder mechanism built into Spring Data repository
infrastructure is useful to build constraining queries over entities
of the repository. We will strip the prefixes findBy
,
find
, readBy
, read
,
getBy
as well as get
from the method and
start parsing the rest of it. At a very basic level you can define
conditions on entity properties and concatenate them with
AND
and OR
.
Example 1.4. Query creation from method names
public interface PersonRepository extends Repository<User, Long> { List<Person> findByEmailAddressAndLastname(EmailAddress emailAddress, String lastname); }
The actual result of parsing that method will of course depend
on the persistence store we create the query for, however, there are
some general things to notice. The expressions are usually property
traversals combined with operators that can be concatenated. As you
can see in the example you can combine property expressions with And
and Or. Beyond that you also get support for various operators like
Between
, LessThan
,
GreaterThan
, Like
for the
property expressions. As the operators supported can vary from
datastore to datastore please consult the according part of the
reference documentation.
Property expressions can just refer to a direct property of
the managed entity (as you just saw in the example above). On query
creation time we already make sure that the parsed property is at a
property of the managed domain class. However, you can also define
constraints by traversing nested properties. Assume
Person
s have Address
es
with ZipCode
s. In that case a method name
of
List<Person> findByAddressZipCode(ZipCode zipCode);
will create the property traversal
x.address.zipCode
. The resolution algorithm starts with
interpreting the entire part (AddressZipCode
) as
property and checks the domain class for a property with that name
(uncapitalized). If it succeeds it just uses that. If not it starts
splitting up the source at the camel case parts from the right side
into a head and a tail and tries to find the according property,
e.g. AddressZip
and Code
. If
we find a property with that head we take the tail and continue
building the tree down from there. As in our case the first split
does not match we move the split point to the left
(Address
, ZipCode
).
Although this should work for most cases, there might be cases
where the algorithm could select the wrong property. Suppose our
Person
class has an addressZip
property as well. Then our algorithm would match in the first split
round already and essentially choose the wrong property and finally
fail (as the type of addressZip
probably has
no code property). To resolve this ambiguity you can use
_
inside your method name to manually define
traversal points. So our method name would end up like so:
List<Person> findByAddress_ZipCode(ZipCode zipCode);
To hand parameters to your query you simply define method parameters as already seen in the examples above. Besides that we will recognizes certain specific types to apply pagination and sorting to your queries dynamically.
Example 1.5. Using Pageable and Sort in query methods
Page<User> findByLastname(String lastname, Pageable pageable); List<User> findByLastname(String lastname, Sort sort); List<User> findByLastname(String lastname, Pageable pageable);
The first method allows you to pass a Pageable
instance to the query method to dynamically add paging to your
statically defined query. Sorting
options are handed via
the Pageable
instance too. If you only
need sorting, simply add a Sort
parameter to your method.
As you also can see, simply returning a
List
is possible as well. We will then
not retrieve the additional metadata required to build the actual
Page
instance but rather simply
restrict the query to lookup only the given range of entities.
Note | |
---|---|
To find out how many pages you get for a query entirely we have to trigger an additional count query. This will be derived from the query you actually trigger by default. |
So now the question is how to create instances and bean definitions for the repository interfaces defined.
The easiest way to do so is by using the Spring namespace that is shipped with each Spring Data module that supports the repository mechanism. Each of those includes a repositories element that allows you to simply define a base package that Spring will scan for you.
<?xml version="1.0" encoding="UTF-8"?> <beans:beans xmlns:beans="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="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"> <repositories base-package="com.acme.repositories" /> </beans:beans>
In this case we instruct Spring to scan
com.acme.repositories and all its sub packages for
interfaces extending Repository
or one
of its sub-interfaces. For each interface found it will register the
persistence technology specific
FactoryBean
to create the according
proxies that handle invocations of the query methods. Each of these
beans will be registered under a bean name that is derived from the
interface name, so an interface of
UserRepository
would be registered
under userRepository
. The base-package
attribute allows the use of wildcards, so that you can have a pattern
of scanned packages.
By default we will pick up every interface extending the
persistence technology specific
Repository
sub-interface located
underneath the configured base package and create a bean instance
for it. However, you might want finer grained control over which
interfaces bean instances get created for. To do this we support the
use of <include-filter />
and
<exclude-filter />
elements inside
<repositories />
. The semantics are exactly
equivalent to the elements in Spring's context namespace. For
details see Spring reference documentation on these
elements.
E.g. to exclude certain interfaces from instantiation as repository, you could use the following configuration:
Example 1.6. Using exclude-filter element
<repositories base-package="com.acme.repositories"> <context:exclude-filter type="regex" expression=".*SomeRepository" /> </repositories>
This would exclude all interfaces ending in
SomeRepository
from being
instantiated.
You can also use the repository infrastructure outside of a
Spring container usage. You will still need to have some of the Spring
libraries on your classpath but you can generally setup repositories
programmatically as well. The Spring Data modules providing repository
support ship a persistence technology specific
RepositoryFactory
that can be used as
follows:
Example 1.7. Standalone usage of repository factory
RepositoryFactorySupport factory = … // Instantiate factory here UserRepository repository = factory.getRepository(UserRepository.class);
Often it is necessary to provide a custom implementation for a few repository methods. Spring Data repositories easily allow you to provide custom repository code and integrate it with generic CRUD abstraction and query method functionality. To enrich a repository with custom functionality you have to define an interface and an implementation for that functionality first and let the repository interface you provided so far extend that custom interface.
Example 1.8. Interface for custom repository functionality
interface UserRepositoryCustom { public void someCustomMethod(User user); }
Example 1.9. Implementation of custom repository functionality
class UserRepositoryImpl implements UserRepositoryCustom { public void someCustomMethod(User user) { // Your custom implementation } }
Note that the implementation itself does not depend on Spring Data and can be a regular Spring bean. So you can use standard dependency injection behaviour to inject references to other beans, take part in aspects and so on.
Example 1.10. Changes to the your basic repository interface
public interface UserRepository extends CrudRepository<User, Long>, UserRepositoryCustom { // Declare query methods here }
Let your standard repository interface extend the custom one. This makes CRUD and custom functionality available to clients.
If you use namespace configuration the repository infrastructure
tries to autodetect custom implementations by looking up classes in
the package we found a repository using the naming conventions
appending the namespace element's attribute
repository-impl-postfix
to the classname. This suffix
defaults to Impl
.
Example 1.11. Configuration example
<repositories base-package="com.acme.repository"> <repository id="userRepository" /> </repositories> <repositories base-package="com.acme.repository" repository-impl-postfix="FooBar"> <repository id="userRepository" /> </repositories>
The first configuration example will try to lookup a class
com.acme.repository.UserRepositoryImpl
to act
as custom repository implementation, where the second example will try
to lookup
com.acme.repository.UserRepositoryFooBar
.
The approach above works perfectly well if your custom implementation uses annotation based configuration and autowiring entirely as it will be treated as any other Spring bean. If your custom implementation bean needs some special wiring you simply declare the bean and name it after the conventions just described. We will then pick up the custom bean by name rather than creating an instance.
Example 1.12. Manual wiring of custom implementations (I)
<repositories base-package="com.acme.repository"> <repository id="userRepository" /> </repositories> <beans:bean id="userRepositoryImpl" class="…"> <!-- further configuration --> </beans:bean>
This also works if you use automatic repository lookup without
defining single <repository />
elements.
In case you are not in control of the implementation bean name
(e.g. if you wrap a generic repository facade around an existing
repository implementation) you can explicitly tell the
<repository />
element which bean to use as custom
implementation by using the repository-impl-ref
attribute.
Example 1.13. Manual wiring of custom implementations (II)
<repositories base-package="com.acme.repository"> <repository id="userRepository" repository-impl-ref="customRepositoryImplementation" /> </repositories> <bean id="customRepositoryImplementation" class="…"> <!-- further configuration --> </bean>
In other cases you might want to add a single method to all of your repository interfaces. So the approach just shown is not feasible. The first step to achieve this is adding and intermediate interface to declare the shared behaviour
Example 1.14. An interface declaring custom shared behaviour
public interface MyRepository<T, ID extends Serializable> extends JpaRepository<T, ID> { void sharedCustomMethod(ID id); }
Now your individual repository interfaces will extend this
intermediate interface instead of the
Repository
interface to include the
functionality declared. The second step is to create an implementation
of this interface that extends the persistence technology specific
repository base class which will then act as a custom base class for the
repository proxies.
Note | |
---|---|
The default behaviour of the Spring |
Example 1.15. Custom repository base class
public class MyRepositoryImpl<T, ID extends Serializable> extends SimpleJpaRepository<T, ID> implements MyRepository<T, ID> { private EntityManager entityManager; // There are two constructors to choose from, either can be used. public MyRepositoryImpl(Class<T> domainClass, EntityManager entityManager) { super(domainClass, entityManager); // This is the recommended method for accessing inherited class dependencies. this.entityManager = entityManager; } public void sharedCustomMethod(ID id) { // implementation goes here } }
The last step is to create a custom repository factory to replace
the default RepositoryFactoryBean
that will in
turn produce a custom RepositoryFactory
. The new
repository factory will then provide your
MyRepositoryImpl
as the implementation of any
interfaces that extend the Repository
interface, replacing the SimpleJpaRepository
implementation you just extended.
Example 1.16. Custom repository factory bean
public class MyRepositoryFactoryBean<R extends JpaRepository<T, I>, T, I extends Serializable> extends JpaRepositoryFactoryBean<R, T, I> { protected RepositoryFactorySupport createRepositoryFactory(EntityManager entityManager) { return new MyRepositoryFactory(entityManager); } private static class MyRepositoryFactory<T, I extends Serializable> extends JpaRepositoryFactory { private EntityManager entityManager; public MyRepositoryFactory(EntityManager entityManager) { super(entityManager); this.entityManager = entityManager; } protected Object getTargetRepository(RepositoryMetadata metadata) { return new MyRepositoryImpl<T, I>((Class<T>) metadata.getDomainClass(), entityManager); } protected Class<?> getRepositoryBaseClass(RepositoryMetadata metadata) { // The RepositoryMetadata can be safely ignored, it is used by the JpaRepositoryFactory //to check for QueryDslJpaRepository's which is out of scope. return MyRepository.class; } } }
Finally you can either declare beans of the custom factory
directly or use the factory-class
attribute of the Spring
namespace to tell the repository infrastructure to use your custom
factory implementation.
Example 1.17. Using the custom factory with the namespace
<repositories base-package="com.acme.repository" factory-class="com.acme.MyRepositoryFactoryBean" />
This chapter documents a set of Spring Data extensions that enable Spring Data usage in a variety of contexts. Currently most of the integration is targeted towards Spring MVC.
Given you are developing a Spring MVC web applications you typically have to resolve domain class ids from URLs. By default it's your task to transform that request parameter or URL part into the domain class to hand it layers below then or execute business logic on the entities directly. This should look something like this:
@Controller @RequestMapping("/users") public class UserController { private final UserRepository userRepository; public UserController(UserRepository userRepository) { userRepository = userRepository; } @RequestMapping("/{id}") public String showUserForm(@PathVariable("id") Long id, Model model) { // Do null check for id User user = userRepository.findOne(id); // Do null check for user // Populate model return "user"; } }
First you pretty much have to declare a repository dependency for
each controller to lookup the entity managed by the controller or
repository respectively. Beyond that looking up the entity is
boilerplate as well as it's always a findOne(…)
call. Fortunately Spring provides means to register custom converting
components that allow conversion between a String
value to an arbitrary type.
For versions up to Spring 3.0 simple Java
PropertyEditor
s had to be used. Thus,
we offer a DomainClassPropertyEditorRegistrar
,
that will look up all Spring Data repositories registered in the
ApplicationContext
and register a
custom PropertyEditor
for the managed
domain class
<bean class="….web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"> <property name="webBindingInitializer"> <bean class="….web.bind.support.ConfigurableWebBindingInitializer"> <property name="propertyEditorRegistrars"> <bean class="org.springframework.data.repository.support.DomainClassPropertyEditorRegistrar" /> </property> </bean> </property> </bean>
If you have configured Spring MVC like this you can turn your controller into the following that reduces a lot of the clutter and boilerplate.
@Controller @RequestMapping("/users") public class UserController { @RequestMapping("/{id}") public String showUserForm(@PathVariable("id") User user, Model model) { // Do null check for user // Populate model return "userForm"; } }
As of Spring 3.0 the
PropertyEditor
support is superseeded
by a new conversion infrstructure that leaves all the drawbacks of
PropertyEditor
s behind and uses a
stateless X to Y conversion approach. We now ship with a
DomainClassConverter
that pretty much mimics
the behaviour of
DomainClassPropertyEditorRegistrar
. To register
the converter you have to declare
ConversionServiceFactoryBean
, register the
converter and tell the Spring MVC namespace to use the configured
conversion service:
<mvc:annotation-driven conversion-service="conversionService" /> <bean id="conversionService" class="….context.support.ConversionServiceFactoryBean"> <property name="converters"> <list> <bean class="org.springframework.data.repository.support.DomainClassConverter"> <constructor-arg ref="conversionService" /> </bean> </list> </property> </bean>
@Controller @RequestMapping("/users") public class UserController { // DI code omitted @RequestMapping public String showUsers(Model model, HttpServletRequest request) { int page = Integer.parseInt(request.getParameter("page")); int pageSize = Integer.parseInt(request.getParameter("pageSize")); model.addAttribute("users", userService.getUsers(pageable)); return "users"; } }
As you can see the naive approach requires the method to contain
an HttpServletRequest
parameter that has
to be parsed manually. We even omitted an appropriate failure handling
which would make the code even more verbose. The bottom line is that the
controller actually shouldn't have to handle the functionality of
extracting pagination information from the request. So we include a
PageableArgumentResolver
that will do the work
for you.
<bean class="….web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"> <property name="customArgumentResolvers"> <list> <bean class="org.springframework.data.web.PageableArgumentResolver" /> </list> </property> </bean>
This configuration allows you to simplify controllers down to something like this:
@Controller @RequestMapping("/users") public class UserController { @RequestMapping public String showUsers(Model model, Pageable pageable) { model.addAttribute("users", userDao.readAll(pageable)); return "users"; } }
The PageableArgumentResolver
will
automatically resolve request parameters to build a
PageRequest
instance. By default it will expect
the following structure for the request parameters:
Table 1.1. Request parameters evaluated by
PageableArgumentResolver
page | The page you want to retrieve |
page.size | The size of the page you want to retrieve |
page.sort | The property that should be sorted by |
page.sort.dir | The direction that should be used for sorting |
In case you need multiple Pageable
s
to be resolved from the request (for multiple tables e.g.) you can use
Spring's @Qualifier
annotation to
distinguish one from another. The request parameters then have to be
prefixed with ${qualifier}_
. So a method signature like
this:
public String showUsers(Model model, @Qualifier("foo") Pageable first, @Qualifier("bar") Pageable second) { … }
you'd have to populate foo_page
and
bar_page
and the according subproperties.
The PageableArgumentResolver
will use a
PageRequest
with the first page and a page size
of 10 by default and will use that in case it can't resolve a
PageRequest
from the request (because of
missing parameters e.g.). You can configure a global default on the
bean declaration directly. In case you might need controller method
specific defaults for the Pageable
simply annotate the method parameter with
@PageableDefaults
and specify page and
page size as annotation attributes:
public String showUsers(Model model,
@PageableDefaults(pageNumber = 0, value = 30) Pageable pageable) { … }
Abstract
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 1.3.3, “Creating repository instances”. Beyond that it
activates persistence exception translation for all beans annotated with
@Repository
to let exceptions being
thrown by the JPA 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:
Table 2.1. Custom JPA-specific attributes of the repositories element
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 Section 2.2.3, “Using JPA NamedQueries” for more information) or
rather annotate your query method with
@Query
(see Section 2.2.4, “Using @Query” for details).
Generally the query creation mechanism for JPA works as described in Section 1.3, “Query methods”. Here's a short example of what a JPA query method translates into:
Example 2.2. 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 Section 1.3.2.2.1, “Property expressions”. Here's an overview of the keywords supported for JPA and what a method containing that keyword essentially translates to.
Table 2.2. Supported keywords inside method names
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 |
Note | |
---|---|
|
Note | |
---|---|
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 2.3. 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 2.4. 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 2.5. 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 2.6. 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); }
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.
Example 2.7. 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 2.8. 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.
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 1.4, “Custom implementations”. 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 2.9. 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 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 QueryHint
s 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 2.10. 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.
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
Specification
s 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
Specification
s 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?
Specification
s 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 2.11. Specifications for a Customer
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 Specification
s. So a client
might use a Specification
as
follows:
Example 2.12. 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 Specification
s 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 2.13. Combined Specifications
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
Specification
s. 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:
Example 2.14. Custom transaction configuration for CRUD
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:
Example 2.15. 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.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.
Example 2.16. 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 | |
---|---|
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 2.17. 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 2.18. Defining lock metadata on CRUD methods
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:
Example 2.19. Auditable
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.
Note | |
---|---|
To minimize boilerplate code Spring Data JPA offers
|
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:
Example 2.20. Auditing configuration orm.xml
<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:
Example 2.21. Activating auditing in the Spring 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:
Example 2.22. AuditorAware
interface
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.
Example 2.23. Using MergingPersistenceUnitmanager
<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
Example 2.24. Using ClasspathScanningPersistenceUnitPostProcessor
<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>
Note | |
---|---|
As of Spring 3.1 a package to scan can be configured on the
|
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 Section 1.3.3, “Creating repository instances”. 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
EntityManager
s 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
@Inject
ed property:
class RepositoryClient { @Inject PersonRepository repository; public void businessMethod() { List<Person> people = repository.findAll(); } }
The <repositories />
element acts as container
for <repository />
elements or can be left empty to
trigger auto detection[1] of repository instances. Attributes defined for
<repositories />
are propagated to contained
<repository />
elements but can be overridden of
course.
Table A.1. Attributes
Name | Description |
---|---|
base-package | Defines the package to be used to be scanned for repository
interfaces extending *Repository
(actual interface is determined by specific Spring Data module) in
auto detection mode. All packages below the configured package
will be scanned, too. In auto configuration mode (no nested
<repository /> elements) wildcards are also
allowed. |
repository-impl-postfix | Defines the postfix to autodetect custom repository
implementations. Classes whose names end with the configured
postfix will be considered as candidates. Defaults to
Impl . |
query-lookup-strategy | Determines the strategy to be used to create finder
queries. See Section 1.3.2.1, “Query lookup strategies”
for details. Defaults to create-if-not-found . |
The <repository />
element can contain all
attributes of <repositories />
except
base-package
. This will result in overriding the values
configured in the surrounding <repositories />
element.
Thus here we will only document extended attributes.
Table A.2. Attributes
id | Defines the id of the bean the repository instance will be registered under as well as the repository interface name. |
custom-impl-ref | Defines a reference to a custom repository implementation bean. |
The following table lists the keywords generally supported by the Spring data repository query derivation mechanism. However consult the store specific documentation for the exact list of supported keywords as some of the ones listed here might not be supported in a particular store.
Table B.1. Query keywords
Logical keyword | Keyword expressions |
---|---|
AFTER | After ,
IsAfter |
BEFORE | Before ,
IsBefore |
CONTAINING | Containing ,
IsContaining ,
Contains |
BETWEEN | Between ,
IsBetween |
ENDING_WITH | EndingWith ,
IsEndingWith ,
EndsWith |
EXISTS | Exists |
FALSE | False ,
IsFalse |
GREATER_THAN | GreaterThan ,
IsGreaterThan |
GREATER_THAN_EQUALS | GreaterThanEqual ,
IsGreaterThanEqual |
IN | In , IsIn |
IS | Is , Equals , (or no
keyword) |
IS_NOT_NULL | NotNull ,
IsNotNull |
IS_NULL | Null , IsNull |
LESS_THAN | LessThan ,
IsLessThan |
LESS_THAN_EQUAL | LessThanEqual ,
IsLessThanEqual |
LIKE | Like , IsLike |
NEAR | Near , IsNear |
NOT | Not , IsNot |
NOT_IN | NotIn ,
IsNotIn |
NOT_LIKE | NotLike ,
IsNotLike |
REGEX | Regex , MatchesRegex ,
Matches |
STARTING_WITH | StartingWith ,
IsStartingWith ,
StartsWith |
TRUE | True , IsTrue |
WITHIN | Within ,
IsWithin |
Aspect oriented programming
Commons DataBase Connection Pools - Library of the Apache
foundation offering pooling implementations of the
DataSource
interface.
Create, Read, Update, Delete - Basic persistence operations
Data Access Object - Pattern to separate persisting logic from the object to be persisted
Pattern to hand a component's dependency to the component from outside, freeing the component to lookup the dependant itself. For more information see http://en.wikipedia.org/wiki/Dependency_Injection.
Object relational mapper implementing JPA - http://www.eclipselink.org
Object relational mapper implementing JPA - http://www.hibernate.org
Java Persistence Api
Java application framework - http://www.springframework.org