added more generalizations

account/src/main/java/de/muehlencord/shared/account/business/AbstractController.java

@@ -33,6 +33,9 @@ import javax.persistence.criteria.CriteriaBuilder;
 import javax.persistence.criteria.CriteriaQuery;
 import javax.persistence.criteria.Order;
 import javax.persistence.criteria.Root;
+import javax.persistence.metamodel.IdentifiableType;
+import javax.persistence.metamodel.Metamodel;
+import javax.persistence.metamodel.SingularAttribute;
 import javax.transaction.Transactional;
 
 /**
@@ -59,7 +62,7 @@ public abstract class AbstractController<T> {
         return em.merge(entity);
     }
 
-    @TransactionAttribute (TransactionAttributeType.REQUIRED)
+    @TransactionAttribute(TransactionAttributeType.REQUIRED)
     @Transactional
     @Lock(LockType.WRITE)
     public void create(T entity) {
@@ -73,7 +76,7 @@ public abstract class AbstractController<T> {
         em.persist(entity);
     }
 
-    @TransactionAttribute (TransactionAttributeType.REQUIRED)
+    @TransactionAttribute(TransactionAttributeType.REQUIRED)
     @Transactional
     @Lock(LockType.WRITE)
     public T update(T entity) {
@@ -85,7 +88,7 @@ public abstract class AbstractController<T> {
         return em.merge(entity);
     }
 
-    @TransactionAttribute (TransactionAttributeType.REQUIRED)
+    @TransactionAttribute(TransactionAttributeType.REQUIRED)
     @Transactional
     @Lock(LockType.WRITE)
     public void delete(T entity) {
@@ -116,4 +119,31 @@ public abstract class AbstractController<T> {
         return query.getResultList();
     }
 
+    /**
+     * returnns null, if the list is empty or null itself. Returns the one
+     * element if there is exactly one element in the list. Otherwise an
+     * exception is thrown
+     *
+     * @param resultList
+     * @return
+     * @throws ControllerException
+     */
+    public T ensureSingleElement(List<T> resultList) throws ControllerException {
+        if ((resultList == null) || (resultList.isEmpty())) {
+            return null;
+        }
+        if (resultList.size() > 1) {
+            throw new ControllerException(ControllerException.CAUSE_TOO_MANY_ROWS, "More than one element found in list - expected exactly one");
+        }
+        return resultList.get(0);
+    }
+
+    private <T> SingularAttribute<? super T, ?> getIdAttribute() {
+        Metamodel m = em.getEntityManagerFactory().getMetamodel();
+        IdentifiableType<T> of = (IdentifiableType<T>) m.managedType(entityClass);
+//        of.getDeclaredId(entityClass).getJavaMember().
+        return of.getId(of.getIdType().getJavaType());
+    }
+      
+
 }

account/src/main/java/de/muehlencord/shared/account/business/ControllerException.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2019 joern.muehlencord.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package de.muehlencord.shared.account.business;
+
+/**
+ *
+ * @author joern.muehlencord
+ */
+public class ControllerException extends Exception {
+
+    private static final long serialVersionUID = 5190280225284514859L;
+    public static final int CAUSE_ALREADY_EXISTS = 1;
+    public static final int CAUSE_NOT_FOUND = 2;
+    public static final int CAUSE_CANNOT_PERSIST = 3;
+    public static final int CAUSE_TOO_MANY_ROWS = 4;
+
+    private final int causeCode;
+
+    /**
+     * Creates a new instance of <code>ControllerException</code> without detail
+     * message.
+     *
+     * @param cause the reason code
+     * @param message an explanation
+     */
+    public ControllerException(int cause, String message) {
+        super(message);
+        this.causeCode = cause;
+    }
+
+    /**
+     *
+     * @param causeCode
+     * @param message
+     * @param cause
+     */
+    public ControllerException(int causeCode, String message, Throwable cause) {
+        super(message, cause);
+        this.causeCode = causeCode;
+    }
+
+    public int getCauseCode() {
+        return causeCode;
+    }
+}