[OLINGO-1430]Enhance metadata serializer to include OnDelete child element for a navigation Property

lib/commons-api/src/main/java/org/apache/olingo/commons/api/edm/EdmNavigationProperty.java

@@ -57,5 +57,7 @@ public interface EdmNavigationProperty extends EdmElement, EdmAnnotatable {
    * @return all referential constraints for this navigation property.
    */
   List<EdmReferentialConstraint> getReferentialConstraints();
+  
+  EdmOnDelete getOnDelete();
 
 }

lib/commons-api/src/main/java/org/apache/olingo/commons/api/edm/EdmOnDelete.java

@@ -0,0 +1,24 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.olingo.commons.api.edm;
+
+public interface EdmOnDelete extends EdmAnnotatable {
+  
+  String getAction();
+}

lib/commons-core/src/main/java/org/apache/olingo/commons/core/edm/EdmNavigationPropertyImpl.java

@@ -26,9 +26,11 @@ import org.apache.olingo.commons.api.edm.Edm;
 import org.apache.olingo.commons.api.edm.EdmEntityType;
 import org.apache.olingo.commons.api.edm.EdmException;
 import org.apache.olingo.commons.api.edm.EdmNavigationProperty;
+import org.apache.olingo.commons.api.edm.EdmOnDelete;
 import org.apache.olingo.commons.api.edm.EdmReferentialConstraint;
 import org.apache.olingo.commons.api.edm.EdmStructuredType;
 import org.apache.olingo.commons.api.edm.provider.CsdlNavigationProperty;
+import org.apache.olingo.commons.api.edm.provider.CsdlOnDelete;
 import org.apache.olingo.commons.api.edm.provider.CsdlReferentialConstraint;
 
 public class EdmNavigationPropertyImpl extends AbstractEdmNamed implements EdmNavigationProperty {
@@ -119,4 +121,10 @@ public class EdmNavigationPropertyImpl extends AbstractEdmNamed implements EdmNa
     }
     return referentialConstraints;
   }
+
+  @Override
+  public EdmOnDelete getOnDelete() {
+    CsdlOnDelete csdlOnDelete = navigationProperty.getOnDelete();
+    return csdlOnDelete != null ? new EdmOnDeleteImpl(edm, csdlOnDelete) : null;
+  }
 }

lib/commons-core/src/main/java/org/apache/olingo/commons/core/edm/EdmOnDeleteImpl.java

@@ -0,0 +1,39 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.olingo.commons.core.edm;
+
+import org.apache.olingo.commons.api.edm.Edm;
+import org.apache.olingo.commons.api.edm.EdmOnDelete;
+import org.apache.olingo.commons.api.edm.provider.CsdlOnDelete;
+
+public class EdmOnDeleteImpl extends AbstractEdmAnnotatable implements EdmOnDelete {
+  
+  private final CsdlOnDelete csdlOnDelete;
+  
+  public EdmOnDeleteImpl(final Edm edm, final CsdlOnDelete csdlOnDelete) {
+    super(edm, csdlOnDelete);
+    this.csdlOnDelete = csdlOnDelete;
+  }
+
+  @Override
+  public String getAction() {
+    return csdlOnDelete.getAction().name();
+  }
+
+}

lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializer.java

@@ -154,6 +154,8 @@ public class MetadataDocumentXmlSerializer {
   private static final String XML_PROPERTY_VALUE = "PropertyValue";
   private static final String XML_BASE_TERM = "BaseTerm";
   private static final String XML_APPLIES_TO = "AppliesTo";
+  private static final String XML_ON_DELETE = "OnDelete";
+  private static final String XML_ON_DELETE_PROPERTY = "Action";
 
   private final ServiceMetadata serviceMetadata;
   private final Map<String, String> namespaceToAlias = new HashMap<>();
@@ -876,6 +878,13 @@ public class MetadataDocumentXmlSerializer {
           writer.writeEndElement();
         }
       }
+      
+      if (navigationProperty.getOnDelete() != null) {
+        writer.writeStartElement(XML_ON_DELETE);
+        writer.writeAttribute(XML_ON_DELETE_PROPERTY, navigationProperty.getOnDelete().getAction());
+        appendAnnotations(writer, navigationProperty.getOnDelete());
+        writer.writeEndElement();
+      }
 
       appendAnnotations(writer, navigationProperty);
 

lib/server-core/src/test/java/org/apache/olingo/server/core/serializer/xml/MetadataDocumentXmlSerializerTest.java

@@ -60,6 +60,9 @@ import org.apache.olingo.commons.api.edm.provider.CsdlEnumMember;
 import org.apache.olingo.commons.api.edm.provider.CsdlEnumType;
 import org.apache.olingo.commons.api.edm.provider.CsdlFunction;
 import org.apache.olingo.commons.api.edm.provider.CsdlFunctionImport;
+import org.apache.olingo.commons.api.edm.provider.CsdlNavigationProperty;
+import org.apache.olingo.commons.api.edm.provider.CsdlOnDelete;
+import org.apache.olingo.commons.api.edm.provider.CsdlOnDeleteAction;
 import org.apache.olingo.commons.api.edm.provider.CsdlParameter;
 import org.apache.olingo.commons.api.edm.provider.CsdlProperty;
 import org.apache.olingo.commons.api.edm.provider.CsdlPropertyRef;
@@ -324,6 +327,9 @@ public class MetadataDocumentXmlSerializerTest {
         + "EntitySet=\"ESAllPrim\"></ActionImport>"));
     assertTrue(metadata.contains("<ActionImport Name=\"AIRTEntityNoES\" Action=\"Alias.UARTEntity\">"
         + "</ActionImport>"));
+    assertTrue(metadata.contains("<NavigationProperty Name=\"NavProperty\" "
+        + "Type=\"Alias.ETAbstract\" Nullable=\"false\"><OnDelete Action=\"Cascade\">"
+        + "<Annotation Term=\"core.Term\"></Annotation></OnDelete></NavigationProperty>"));
   }
 
   @Test
@@ -499,6 +505,13 @@ public class MetadataDocumentXmlSerializerTest {
     private final CsdlProperty propertyString = new CsdlProperty()
     .setName("PropertyString")
     .setType(nameString);
+    
+    private final CsdlNavigationProperty navProperty = new CsdlNavigationProperty()
+        .setName("NavProperty")
+        .setType(nameETAbstract)
+        .setNullable(false)
+        .setOnDelete(new CsdlOnDelete().setAction(CsdlOnDeleteAction.Cascade)
+            .setAnnotations(Arrays.asList(new CsdlAnnotation().setTerm("core.Term"))));
 
     private final FullQualifiedName nameCTTwoPrim = new FullQualifiedName(nameSpace, "CTTwoPrim");
     private final FullQualifiedName nameCTTwoPrimBase = new FullQualifiedName(nameSpace, "CTTwoPrimBase");
@@ -543,7 +556,8 @@ public class MetadataDocumentXmlSerializerTest {
         return new CsdlEntityType()
         .setName("ET")
         .setKey(Collections.singletonList(new CsdlPropertyRef().setName("PropertyInt16")))
-        .setProperties(Collections.singletonList(propertyInt16_NotNullable));
+        .setProperties(Collections.singletonList(propertyInt16_NotNullable))
+        .setNavigationProperties(Collections.singletonList(navProperty));
       }
       return null;
     }
@@ -809,6 +823,9 @@ public class MetadataDocumentXmlSerializerTest {
       } else if (new FullQualifiedName("ns", "Term4").equals(termName)) {
         return new CsdlTerm().setType("Edm.String").setName("Term4").setBaseTerm("namespace.Term1");
 
+      } else if (new FullQualifiedName("core", "Term").equals(termName)) {
+        return new CsdlTerm().setType("Edm.String").setName("Term").setBaseTerm("core.Term");
+
       }
       return null;
     }