[Janos#16] Navigation fixes

EntityNavigation.md

@@ -0,0 +1,130 @@
+# Navigation between entities
+
+The class `AnnotationHelper.AnnotatedNavInfo` is constructed by the helper method
+`Annotation#getCommonNavigationInfo` to describe the annotated navigation between
+two entities.
+
+## Example code fragments
+
+```java
+@EdmEntityType(name = "Building")
+@EdmEntitySet(name = "Buildings")
+public class Building {
+  @EdmKey @EdmProperty(name = "ID")
+  private String id;
+  @EdmProperty(name = "Name")
+  private String name;
+  @EdmNavigationProperty(toMultiplicity = Multiplicity.MANY)
+  private List<Room> rooms = new ArrayList<>();
+  // etc.
+}
+```
+
+```java
+@EdmEntityType(name = "Room")
+@EdmEntitySet(name = "Rooms")
+public class Room {
+  @EdmKey @EdmProperty(name = "ID")
+  private String id;
+  @EdmProperty(name = "Name")
+  private String name;
+  @EdmNavigationProperty
+  private Building building;
+  // etc.
+}
+```
+
+```java
+@EdmEntityType(name = "Closet")
+@EdmEntitySet(name = "Closets")
+public class Closet {
+  @EdmKey @EdmProperty(name = "ID")
+  private String id;
+  @EdmProperty(name = "Name")
+  private String name;
+  @EdmNavigationProperty()
+  private Building building;
+  // etc.
+}
+```
+
+```java
+@EdmEntityType(name = "Task")
+@EdmEntitySet(name = "Tasks")
+public class Task {
+  @EdmKey @EdmProperty(name = "ID")
+  private String id;
+  @EdmProperty(name = "Name")
+  private String name;
+  @EdmNavigationProperty(multiplicity = Multiplicity.MANY)
+  private List<Task> subTasks = new ArrayList<>();
+  // etc.
+}
+```
+
+## Bi-directional navigation
+
+A class has a navigation property to another class and the second class
+has a navigation property back to the first.
+
+In the above code fragments, the relationship between `Building` and `Room` is
+bi-directional. A room has a link to the building where it is found and a
+building maintains a list of its rooms.
+
+A call to `AnnotationHelper.getCommonNavigation(Room.class, Building.class)`
+returns an `AnnotatedNavInfo` instance with:
+
+* `isBiDirectional()` = `true`
+* `getFromField()` = `building`
+* `getToMultiplicity()` = `ONE`
+* `getToField()` = `rooms`
+* `getFromMultiplicity()` = `MANY`
+
+A call to `AnnotationHelper.getCommonNavigation(Building.class, Room.class)`
+returns an `AnnotatedNavInfo` instance with:
+
+* `isBiDirectional()` = `true`
+* `getFromField()` = `rooms`
+* `getToMultiplicity()` = `MANY`
+* `getToField()` = `building`
+* `getFromMultiplicity()` = `ONE`
+
+## Uni-directional navigation
+
+A class has a navigation property to another class but the second class
+does not have a navigation property back to the first.
+
+In the above code fragments, the relationship between `Building` and `Closet` is
+uni-directional. A closet has a link to the building where it is found but a
+building does not have a list of any closets.
+
+A call to `AnnotationHelper.getCommonNavigation(Closet.class, Building.class)`
+returns an `AnnotatedNavInfo` instance with:
+
+* `isBiDirectional()` = `false`
+* `getFromField()` = `building`
+* `getFromMultiplicity()` = `ONE`
+* `getToField()` = `null`
+* `getToMultiplicity()` = `ONE`
+
+A call to `AnnotationHelper.getCommonNavigation(Building.class, Closet.class)`
+returns an `AnnotatedNavInfo` instance with:
+
+* `isBiDirectional()` = `false`
+* `getFromField()` = `null`
+* `getFromMultiplicity()` = `ONE`
+* `getToField()` = `closet`
+* `getToMultiplicity()` = `ONE`
+
+## Self-navigation
+
+Self-navigation is a special case of uni-directional navigation.
+
+A call to `AnnotationHelper.getCommonNavigation(Task.class, Task.class)`
+returns an `AnnotatedNavInfo` instance with:
+
+* `isBiDirectional()` = `false`
+* `getFromField()` = `subTasks`
+* `getToMultiplicity()` = `ONE`
+* `getToField()` = `null`
+* `getFromMultiplicity()` = `ONE`

janos-core/src/main/java/org/apache/olingo/odata2/janos/processor/core/data/source/AnnotationDataSource.java

@@ -125,7 +125,7 @@ public Object readRelatedData(final EdmEntitySet sourceEntitySet, final Object s
     AnnotationHelper.AnnotatedNavInfo navInfo = ANNOTATION_HELPER.getCommonNavigationInfo(
         sourceStore.getDataTypeClass(), targetStore.getDataTypeClass());
     final Field sourceField;
-    if(navInfo.isBiDirectional()) {
+    if (navInfo.getFromField() == null) {
       sourceField = navInfo.getToField();
     } else {
       sourceField = navInfo.getFromField();
@@ -162,10 +162,14 @@ private List<Object> readResultData(final DataStore<?> targetStore, final Object
         Map<String, Object> keyName2Value = 
                 ANNOTATION_HELPER.getValueForAnnotatedFields(sourceData, EdmKey.class);
         Field toField = navInfo.getToField();
-        Object backInstance = ClassHelper.getFieldValue(targetInstance, toField);
-        boolean keyMatch = ANNOTATION_HELPER.keyMatch(backInstance, keyName2Value);
-        if(keyMatch) {
+        if (toField == null) {
           resultData.add(targetInstance);
+        } else {
+          Object backInstance = ClassHelper.getFieldValue(targetInstance, toField);
+          boolean keyMatch = ANNOTATION_HELPER.keyMatch(backInstance, keyName2Value);
+          if (keyMatch) {
+            resultData.add(targetInstance);
+          }
         }
       } else if (targetStore.isKeyEqualChecked(targetInstance, navigationInstance)) {
         resultData.add(targetInstance);