CCM NG: Variante der findById Methode für fetchJoins erstellen erstellen (#2805)

git-svn-id: https://svn.libreccm.org/ccm/ccm_ng@5254 8810af33-2d31-482b-a856-94f89814c4df

ccm-core/src/main/java/org/libreccm/core/AbstractEntityRepository.java

@@ -28,6 +28,7 @@ import java.util.Optional;
 import javax.inject.Inject;
 import javax.persistence.EntityGraph;
 import javax.persistence.EntityManager;
+import javax.persistence.NoResultException;
 import javax.persistence.TypedQuery;
 import javax.persistence.criteria.CriteriaBuilder;
 import javax.persistence.criteria.CriteriaQuery;
@@ -127,8 +128,8 @@ public abstract class AbstractEntityRepository<K, E> implements Serializable {
     /**
      * Used by some methods to create queries using the JPA Criteria API.
      *
-     * @return The name of the ID attribute/property for entities managed by
+     * @return The name of the ID attribute/property for entities managed by a
-     * a repository.
+     *         repository.
      */
     public abstract String getIdAttributeName();
 
@@ -176,6 +177,32 @@ public abstract class AbstractEntityRepository<K, E> implements Serializable {
                                                       hints));
     }
 
+    @Transactional(Transactional.TxType.REQUIRED)
+    public Optional<E> findById(final K entityId,
+                                final String... fetchJoins) {
+
+        Objects.requireNonNull(entityId);
+
+        final CriteriaBuilder builder = entityManager.getCriteriaBuilder();
+        final CriteriaQuery<E> criteriaQuery = builder
+            .createQuery(getEntityClass());
+        final Root<E> from = criteriaQuery.from(getEntityClass());
+        criteriaQuery.from(getEntityClass());
+        for (final String fetchJoin : fetchJoins) {
+            from.fetch(fetchJoin);
+        }
+
+        criteriaQuery
+            .where(builder.equal(from.get(getIdAttributeName()), entityId));
+
+        final TypedQuery<E> query = entityManager.createQuery(criteriaQuery);
+        try {
+            return Optional.of(query.getSingleResult());
+        } catch (NoResultException ex) {
+            return Optional.empty();
+        }
+    }
+
     /**
      * Finds all instances of the entity of the type this repository is
      * responsible for.