Spring Data JPA @Query

1. Panoramica

Spring Data offre molti modi per definire una query che possiamo eseguire. Uno di questi è l' annotazione @Query .

In questo tutorial, dimostreremo come utilizzare l' annotazione @Query in Spring Data JPA per eseguire query JPQL e SQL native.

Mostreremo anche come costruire una query dinamica quando l' annotazione @Query non è sufficiente.

2. Selezionare Query

Per definire l'SQL da eseguire per un metodo del repository Spring Data, possiamo annotare il metodo con l' annotazione @Query - il suo attributo value contiene JPQL o SQL da eseguire.

L' annotazione @Query ha la precedenza sulle query denominate, che sono annotate con @NamedQuery o definite in un file orm.xml .

È un buon approccio posizionare una definizione di query appena sopra il metodo all'interno del repository piuttosto che all'interno del nostro modello di dominio come query con nome. Il repository è responsabile della persistenza, quindi è un posto migliore per archiviare queste definizioni.

2.1. JPQL

Per impostazione predefinita, la definizione della query utilizza JPQL.

Diamo un'occhiata a un semplice metodo di repository che restituisce entità utente attive dal database:

@Query("SELECT u FROM User u WHERE u.status = 1") Collection findAllActiveUsers(); 

2.2. Nativo

Possiamo usare anche SQL nativo per definire la nostra query. Tutto quello che dobbiamo fare è impostare il valore dell'attributo nativeQuery su true e definire la query SQL nativa nell'attributo value dell'annotazione:

@Query( value = "SELECT * FROM USERS u WHERE u.status = 1", nativeQuery = true) Collection findAllActiveUsersNative(); 

3. Definire l'ordine in una query

Possiamo passare un parametro aggiuntivo di tipo Sort a una dichiarazione del metodo Spring Data che ha l' annotazione @Query . Verrà tradotto nella clausola ORDER BY che viene passata al database.

3.1. Ordinamento per metodi JPA forniti e derivati

Per i metodi che otteniamo fuori dagli schemi come findAll (Sort) o quelli generati dall'analisi delle firme del metodo, possiamo usare solo le proprietà degli oggetti per definire il nostro ordinamento :

userRepository.findAll(new Sort(Sort.Direction.ASC, "name")); 

Ora immagina di voler ordinare in base alla lunghezza di una proprietà name:

userRepository.findAll(new Sort("LENGTH(name)")); 

Quando eseguiamo il codice sopra, riceveremo un'eccezione:

org.springframework.data.mapping.PropertyReferenceException: Nessuna proprietà lENGTH (nome) trovata per il tipo User!

3.2. JPQL

Quando usiamo JPQL per una definizione di query, Spring Data può gestire l'ordinamento senza alcun problema : tutto ciò che dobbiamo fare è aggiungere un parametro del metodo di tipo Sort :

@Query(value = "SELECT u FROM User u") List findAllUsers(Sort sort); 

Possiamo chiamare questo metodo e passare un parametro Sort , che ordinerà il risultato in base alla proprietà name dell'oggetto User :

userRepository.findAllUsers(new Sort("name"));

E poiché abbiamo utilizzato l' annotazione @Query , possiamo utilizzare lo stesso metodo per ottenere l'elenco ordinato degli utenti in base alla lunghezza dei loro nomi:

userRepository.findAllUsers(JpaSort.unsafe("LENGTH(name)")); 

È fondamentale utilizzare JpaSort.unsafe () per creare un'istanza di oggetto Sort .

Quando usiamo:

new Sort("LENGTH(name)"); 

quindi riceveremo esattamente la stessa eccezione che abbiamo visto sopra per il metodo findAll () .

When Spring Data discovers the unsafe Sort order for a method that uses the @Query annotation, then it just appends the sort clause to the query — it skips checking whether the property to sort by belongs to the domain model.

3.3. Native

When the @Query annotation uses native SQL, then it's not possible to define a Sort.

If we do, we'll receive an exception:

org.springframework.data.jpa.repository.query.InvalidJpaQueryMethodException: Cannot use native queries with dynamic sorting and/or pagination

As the exception says, the sort isn't supported for native queries. The error message gives us a hint that pagination will cause an exception too.

However, there is a workaround that enables pagination, and we'll cover it in the next section.

4. Pagination

Pagination allows us to return just a subset of a whole result in a Page. This is useful, for example, when navigating through several pages of data on a web page.

Another advantage of pagination is that the amount of data sent from server to client is minimized. By sending smaller pieces of data, we can generally see an improvement in performance.

4.1. JPQL

Using pagination in the JPQL query definition is straightforward:

@Query(value = "SELECT u FROM User u ORDER BY id") Page findAllUsersWithPagination(Pageable pageable); 

We can pass a PageRequest parameter to get a page of data.

Pagination is also supported for native queries but requires a little bit of additional work.

4.2. Native

We can enable pagination for native queries by declaring an additional attribute countQuery.

This defines the SQL to execute to count the number of rows in the whole result:

@Query( value = "SELECT * FROM Users ORDER BY id", countQuery = "SELECT count(*) FROM Users", nativeQuery = true) Page findAllUsersWithPagination(Pageable pageable);

4.3. Spring Data JPA Versions Prior to 2.0.4

The above solution for native queries works fine for Spring Data JPA versions 2.0.4 and later.

Prior to that version, when we try to execute such a query, we'll receive the same exception we described in the previous section on sorting.

We can overcome this by adding an additional parameter for pagination inside our query:

@Query( value = "SELECT * FROM Users ORDER BY id \n-- #pageable\n", countQuery = "SELECT count(*) FROM Users", nativeQuery = true) Page findAllUsersWithPagination(Pageable pageable);

In the above example, we add “\n– #pageable\n” as the placeholder for the pagination parameter. This tells Spring Data JPA how to parse the query and inject the pageable parameter. This solution works for the H2 database.

We've covered how to create simple select queries via JPQL and native SQL. Next, we'll show how to define additional parameters.

5. Indexed Query Parameters

There are two possible ways that we can pass method parameters to our query: indexed and named parameters.

In this section, we'll cover indexed parameters.

5.1. JPQL

For indexed parameters in JPQL, Spring Data will pass method parameters to the query in the same order they appear in the method declaration:

@Query("SELECT u FROM User u WHERE u.status = ?1") User findUserByStatus(Integer status); @Query("SELECT u FROM User u WHERE u.status = ?1 and u.name = ?2") User findUserByStatusAndName(Integer status, String name); 

For the above queries, the status method parameter will be assigned to the query parameter with index 1, and the name method parameter will be assigned to the query parameter with index 2.

5.2. Native

Indexed parameters for the native queries work exactly in the same way as for JPQL:

@Query( value = "SELECT * FROM Users u WHERE u.status = ?1", nativeQuery = true) User findUserByStatusNative(Integer status);

In the next section, we'll show a different approach: passing parameters via name.

6. Named Parameters

We can also pass method parameters to the query using named parameters. We define these using the @Param annotation inside our repository method declaration.

Each parameter annotated with @Param must have a value string matching the corresponding JPQL or SQL query parameter name. A query with named parameters is easier to read and is less error-prone in case the query needs to be refactored.

6.1. JPQL

As mentioned above, we use the @Param annotation in the method declaration to match parameters defined by name in JPQL with parameters from the method declaration:

@Query("SELECT u FROM User u WHERE u.status = :status and u.name = :name") User findUserByStatusAndNameNamedParams( @Param("status") Integer status, @Param("name") String name); 

Note that in the above example, we defined our SQL query and method parameters to have the same names, but it's not required as long as the value strings are the same:

@Query("SELECT u FROM User u WHERE u.status = :status and u.name = :name") User findUserByUserStatusAndUserName(@Param("status") Integer userStatus, @Param("name") String userName); 

6.2. Native

For the native query definition, there is no difference in how we pass a parameter via the name to the query in comparison to JPQL — we use the @Param annotation:

@Query(value = "SELECT * FROM Users u WHERE u.status = :status and u.name = :name", nativeQuery = true) User findUserByStatusAndNameNamedParamsNative( @Param("status") Integer status, @Param("name") String name);

7. Collection Parameter

Let's consider the case when the where clause of our JPQL or SQL query contains the IN (or NOT IN) keyword:

SELECT u FROM User u WHERE u.name IN :names

In this case, we can define a query method that takes Collection as a parameter:

@Query(value = "SELECT u FROM User u WHERE u.name IN :names") List findUserByNameList(@Param("names") Collection names);

As the parameter is a Collection, it can be used with List, HashSet, etc.

Next, we'll show how to modify data with the @Modifying annotation.

8. Update Queries With @Modifying

We can use the @Query annotation to modify the state of the database by also adding the @Modifying annotation to the repository method.

8.1. JPQL

The repository method that modifies the data has two differences in comparison to the select query — it has the @Modifying annotation and, of course, the JPQL query uses update instead of select:

@Modifying @Query("update User u set u.status = :status where u.name = :name") int updateUserSetStatusForName(@Param("status") Integer status, @Param("name") String name); 

The return value defines how many rows the execution of the query updated. Both indexed and named parameters can be used inside update queries.

8.2. Native

We can modify the state of the database also with a native query. We just need to add the @Modifying annotation:

@Modifying @Query(value = "update Users u set u.status = ? where u.name = ?", nativeQuery = true) int updateUserSetStatusForNameNative(Integer status, String name);

8.3. Inserts

To perform an insert operation, we have to both apply @Modifying and use a native query since INSERT is not a part of the JPA interface:

@Modifying @Query( value = "insert into Users (name, age, email, status) values (:name, :age, :email, :status)", nativeQuery = true) void insertUser(@Param("name") String name, @Param("age") Integer age, @Param("status") Integer status, @Param("email") String email);

9. Dynamic Query

Often, we'll encounter the need for building SQL statements based on conditions or data sets whose values are only known at runtime. And in those cases, we can't just use a static query.

9.1. Example of a Dynamic Query

For example, let's imagine a situation where we need to select all the users whose email is LIKE one from a set defined at runtime — email1, email2, …, emailn:

SELECT u FROM User u WHERE u.email LIKE '%email1%' or u.email LIKE '%email2%' ... or u.email LIKE '%emailn%'

Since the set is dynamically constructed, we can't know at compile-time how many LIKE clauses to add.

In this case, we can't just use the @Query annotation since we can't provide a static SQL statement.

Instead, by implementing a custom composite repository, we can extend the base JpaRepository functionality and provide our own logic for building a dynamic query. Let's take a look at how to do this.

9.2. Custom Repositories and the JPA Criteria API

Luckily for us, Spring provides a way for extending the base repository through the use of custom fragment interfaces. We can then link them together to create a composite repository.

We'll start by creating a custom fragment interface:

public interface UserRepositoryCustom { List findUserByEmails(Set emails); }

And then we'll implement it:

public class UserRepositoryCustomImpl implements UserRepositoryCustom { @PersistenceContext private EntityManager entityManager; @Override public List findUserByEmails(Set emails) { CriteriaBuilder cb = entityManager.getCriteriaBuilder(); CriteriaQuery query = cb.createQuery(User.class); Root user = query.from(User.class); Path emailPath = user.get("email"); List predicates = new ArrayList(); for (String email : emails) { predicates.add(cb.like(emailPath, email)); } query.select(user) .where(cb.or(predicates.toArray(new Predicate[predicates.size()]))); return entityManager.createQuery(query) .getResultList(); } }

As shown above, we leveraged the JPA Criteria API to build our dynamic query.

Also, we need to make sure to include the Impl postfix in the class name. Spring will search the UserRepositoryCustom implementation as UserRepositoryCustomImpl. Since fragments are not repositories by themselves, Spring relies on this mechanism to find the fragment implementation.

9.3. Extending the Existing Repository

Notice that all the query methods from section 2 through section 7 are in the UserRepository.

So, now we'll integrate our fragment by extending the new interface in the UserRepository:

public interface UserRepository extends JpaRepository, UserRepositoryCustom { // query methods from section 2 - section 7 }

9.4. Using the Repository

And finally, we can call our dynamic query method:

Set emails = new HashSet(); // filling the set with any number of items userRepository.findUserByEmails(emails); 

We've successfully created a composite repository and called our custom method.

10. Conclusion

In questo articolo, abbiamo trattato diversi modi per definire le query nei metodi del repository JPA Spring Data utilizzando l' annotazione @Query .

Abbiamo anche imparato come implementare un repository personalizzato e creare una query dinamica.

Come sempre, gli esempi di codice completi utilizzati in questo articolo sono disponibili su GitHub.