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While method expressions are fine for simple queries, they will often reach their limit once things get slightly more complex. Another aspect is the way you want to use JPA: The recommended approach using JPA for best performance is over named queries. To help incorporate those use cases, the CDI Query module supports also annotating methods for more control on the generated query.
The simples way to define a specific query is by annotation a method and providing the JPQL query string which has to be executed. In code, this looks like the following sample:
public interface PersonDao extends EntityDao<Person, Long> {
@Query("select count(p) from Person p where p.age > ?1")
Long countAllOlderThan(int minAge);
}
The parameter binding in the query corresponds to the argument index in the method.
You can also refer to a named query which is constructed and executed automatically. The @Query
annotation has a named attribute which corresponds to the query name:
@Entity
@NamedQueries({
@NamedQuery(name = Person.BY_MIN_AGE,
query = "select count(p) from Person p where p.age > ?1 order by p.age asc")
})
public class Person {
public static final String BY_MIN_AGE = "person.byMinAge";
...
}
public interface PersonDao extends EntityDao<Person, Long> {
@Query(named = Person.BY_MIN_AGE)
Long countAllOlderThan(int minAge);
}
Same as before, the parameter binding correspons to the argument index in the method. If the named query requires
named parameters to be used, this can be done by annotating the arguments with the @QueryParam
annotation.
Java does not preserve method parameter names, that's why the annotation is needed.
@NamedQuery(name = Person.BY_MIN_AGE,
query = "select count(p) from Person p where p.age > :minAge order by p.age asc")
public interface PersonDao extends EntityDao<Person, Long> {
@Query(named = Person.BY_MIN_AGE)
Long countAllOlderThan(@QueryParam("minAge") int minAge);
}
It is also possible to set a native SQL query in the annotation. The @Query
annotation has a sql attribute which corresponds to the SQL query to execute:
@Entity
@Table(name = "PERSON_TABLE")
public class Person {
...
}
public interface PersonDao extends EntityDao<Person, Long> {
@Query(sql = "SELECT * FROM PERSON_TABLE p WHERE p.AGE > ?1")
List<Person> findAllOlderThan(int minAge);
}
Beside providing a query string or reference, the @Query annotation provides also two more
attributes:
public interface PersonDao extends EntityDao<Person, Long> {
@Query(named = Person.BY_MIN_AGE, max = 10, lock = LockModeType.PESSIMISTIC_WRITE)
List<Person> findAllForUpdate(int minAge);
}
| Name | Description |
|---|---|
max | Limits the number of results. |
lock |
Use a specific LockModeType to execute the query.
|
Note that these options can also be applied to Chapter 3, Query Method Expressions