Fix HibernateException: could not re-associate uninitialized transient

... collection". This is caused because the object being saved has a
lazy-loading collection that is not loaded, but it is no longer attached
to a session. The solution is to merge (re-attach) the object to the
current session before doing something with it again.

The merge operation cannot modify the current object, but returns a new
(proxy) object that must be used from now on. To make this
counterintuitive behaviour of the API more obvious, the CheckReturnValue
annotation was introduced, which is evaluated by Spotbugs, which results
in a Spotbugs alert if it is ignored.

Kitodo-DataManagement/pom.xml

@@ -87,6 +87,12 @@
             <groupId>org.hibernate</groupId>
             <artifactId>hibernate-jcache</artifactId>
         </dependency>
+        <dependency>
+            <groupId>com.github.spotbugs</groupId>
+            <artifactId>spotbugs-annotations</artifactId>
+            <version>${spotbugs-maven-plugin.version}</version>
+            <scope>provided</scope>
+        </dependency>
         <dependency>
             <groupId>org.ehcache</groupId>
             <artifactId>ehcache</artifactId>

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

@@ -11,6 +11,8 @@
 
 package org.kitodo.data.database.persistence;
 
+import edu.umd.cs.findbugs.annotations.CheckReturnValue;
+
 import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -163,6 +165,17 @@ public void evict(T baseBean) {
         evictObject(baseBean);
     }
 
+    /**
+     * Merge given bean object.
+     *
+     * @param baseBean
+     *            bean to Merge
+     */
+    @CheckReturnValue
+    public T merge(T baseBean) {
+        return mergeObject(baseBean);
+    }
+
     /**
      * Retrieves BaseBean objects from database by given query.
      *
@@ -413,6 +426,20 @@ private void evictObject(T object) {
         }
     }
 
+    /**
+     * Merge object into the session.
+     *
+     * @param object
+     *            to be associated with the session
+     */
+    @SuppressWarnings("unchecked")
+    @CheckReturnValue
+    private T mergeObject(T object) {
+        try (Session session = HibernateUtil.getSession()) {
+            return (T) session.merge(object);
+        }
+    }
+
     /**
      * Refresh object associated with the session.
      *

Kitodo/src/main/java/org/kitodo/production/services/data/ProcessService.java

@@ -1877,9 +1877,10 @@ public static void deleteProcess(Process processToDelete) throws DataException,
             parent.getChildren().remove(processToDelete);
             processToDelete.setParent(null);
             MetadataEditor.removeLink(parent, processToDelete.getId());
-            ServiceManager.getProcessService().save(processToDelete);
+            processToDelete = ServiceManager.getProcessService().merge(processToDelete);
             ServiceManager.getProcessService().save(parent);
         }
+        processToDelete = ServiceManager.getProcessService().merge(processToDelete);
         List<Batch> batches = new CopyOnWriteArrayList<>(processToDelete.getBatches());
         for (Batch batch : batches) {
             batch.getProcesses().remove(processToDelete);

Kitodo/src/main/java/org/kitodo/production/services/data/base/SearchDatabaseService.java

@@ -11,6 +11,8 @@
 
 package org.kitodo.production.services.data.base;
 
+import io.reactivex.annotations.CheckReturnValue;
+
 import java.util.EnumMap;
 import java.util.List;
 import java.util.Map;
@@ -170,6 +172,11 @@ public void evict(T baseBean) {
         this.dao.evict(baseBean);
     }
 
+    @CheckReturnValue
+    public T merge(T baseBean) {
+        return this.dao.merge(baseBean);
+    }
+
     /**
      * Refresh given bean object.
      *