Adds a function for ID-based database searching, and logging

Kitodo-DataManagement/src/main/java/org/kitodo/data/database/persistence/BaseDAO.java

@@ -23,6 +23,8 @@
 
 import javax.persistence.PersistenceException;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.hibernate.Hibernate;
 import org.hibernate.Session;
 import org.hibernate.Transaction;
@@ -38,6 +40,7 @@
  * Base class for DAOs.
  */
 public abstract class BaseDAO<T extends BaseBean> implements Serializable {
+    private final Logger logger = LogManager.getLogger(getClass());
 
     private static final Object lockObject = new Object();
 
@@ -185,6 +188,7 @@ public List<T> getByQuery(String query, Map<String, Object> parameters, int firs
             addParameters(q, parameters);
             return q.list();
         } catch (SQLGrammarException e) {
+            logger.catching(e);
             return Collections.emptyList();
         }
     }
@@ -284,6 +288,44 @@ static void removeObject(Class<?> cls, Integer objectId) throws DAOException {
         }
     }
 
+    /**
+     * Returns the list of object IDs returned by a query.
+     * 
+     * <p>
+     * To display lists that are many pages long, based on conditional database
+     * queries, the IDs of the objects to be displayed are first determined in
+     * the database without deserializing the objects. The required section of
+     * objects can then be retrieved later using the list. However, basic
+     * information required for list pagination, such as the total length of the
+     * list, and a fixed list position for each object, is already given.
+     * 
+     * <p>
+     * Not loading all potential display candidates at the time of request
+     * speeds up the display significantly, or even makes it usable at all for
+     * larger data sets (considering several 100k records in a table), thus
+     * enabling a smooth user experience.
+     * 
+     * @param query
+     *            HQL query kind of "SELECT id FROM ClassName WHERE …"
+     * @param parameters
+     *            query parameters. May be {@code null}.
+     * @return list of object IDs
+     */
+    public List<? extends Number> getIdsByQuery(String query, Map<String, Object> parameters) {
+        String objectClass = getClass().getName().replaceFirst("DAO$", "");
+        if (!(query.substring(0, 15).equalsIgnoreCase("SELECT id FROM ")
+                && query.substring(15, 16 + objectClass.length()).equals(objectClass.concat(" ")))) {
+            throw new IllegalArgumentException("query must start with 'SELECT id FROM " + objectClass
+                    + "', but was: " + query);
+        }
+        try (Session session = HibernateUtil.getSession()) {
+            Query<?> questioner = session.createQuery(query);
+            addParameters(questioner, parameters);
+            List<?> answer = questioner.list();
+            return answer.stream().map(Number.class::cast).collect(Collectors.toList());
+        }
+    }
+
     /**
      * Initialize child list of objects for given base bean.
      *