Make the change in Document.java

Execution, IDocumentField and IDocumentChangesCollector: minor
improvements

verify if lookup value is still valid
#551

src/main/java/de/metas/ui/web/process/ProcessRestController.java

@@ -219,8 +219,11 @@ public List<JSONDocument> processParametersChangeEvents(
 		final IProcessInstancesRepository instancesRepository = getRepository(processId);
 
 		return Execution.callInNewExecution("", () -> {
-			final IDocumentChangesCollector changesCollector = Execution.getCurrentDocumentChangesCollectorOrNull();
+
+			final IDocumentChangesCollector changesCollector = Execution.getCurrentDocumentChangesCollectorOrNull(); // get our collector to fill with the changes that we will record
+
 			instancesRepository.forProcessInstanceWritable(pinstanceId, changesCollector, processInstance -> {
+
 				processInstance.processParameterValueChanges(events, REASON_Value_DirectSetFromCommitAPI);
 				return null; // void
 			});

src/main/java/de/metas/ui/web/window/controller/Execution.java

@@ -94,7 +94,7 @@ public static IDocumentChangesCollector getCurrentDocumentChangesCollector()
 	}
 
 	/**
-	 * @return actual {@link IDocumentChangesCollector} or {@link NullDocumentChangesCollector}
+	 * @return actual {@link IDocumentChangesCollector} or {@link NullDocumentChangesCollector}. Never returns {@code null}.
 	 */
 	public static IDocumentChangesCollector getCurrentDocumentChangesCollectorOrNull()
 	{

src/main/java/de/metas/ui/web/window/model/Document.java

@@ -1137,7 +1137,7 @@ public void processValueChange(final String fieldName, final Object value, final
 		}
 	}
 
-	public void processValueChanges(final List<JSONDocumentChangedEvent> events, final ReasonSupplier reason) throws DocumentFieldReadonlyException
+	public void processValueChanges(@NonNull final List<JSONDocumentChangedEvent> events, final ReasonSupplier reason) throws DocumentFieldReadonlyException
 	{
 		for (final JSONDocumentChangedEvent event : events)
 		{
@@ -1451,6 +1451,21 @@ else if (DependencyType.LookupValues == triggeringDependencyType)
 			final boolean lookupValuesStaled = documentField.setLookupValuesStaled(triggeringFieldName);
 			if (lookupValuesStaled && !lookupValuesStaledOld)
 			{
+				// https://github.com/metasfresh/metasfresh-webui-api/issues/551 check if we can leave the old value as it is
+				final Object valueOld = documentField.getValue();
+				if (valueOld != null)
+				{
+					final boolean currentValueStillValid = documentField.getLookupValues() // because we did setLookupValuesStaled(), this causes a reload
+							.stream()
+							.anyMatch(value -> Objects.equals(value, valueOld)); // check if the current value is still value after we reloaded the list
+					if(!currentValueStillValid)
+					{
+						documentField.setValue(null, changesCollector);
+						changesCollector.collectValueIfChanged(documentField, valueOld, reason);
+					}
+				}
+
+				// https://github.com/metasfresh/metasfresh-webui-frontend/issues/1165 - the value was not stale, but now it is => notify the frontend so it shall invalidate its cache
 				changesCollector.collectLookupValuesStaled(documentField, reason);
 			}
 		}

src/main/java/de/metas/ui/web/window/model/IDocumentChangesCollector.java

@@ -36,7 +36,7 @@ public interface IDocumentChangesCollector
 	/**
 	 * Mark the changes of given document path as primary changes.
 	 * 
-	 * Primary changes are those changes which are on a document which was directly references by REST endpoint.
+	 * Primary changes are those changes which are on a document which was directly referenced by REST endpoint.
 	 * 
 	 * @param documentPath
 	 */

src/main/java/de/metas/ui/web/window/model/IDocumentField.java

@@ -68,6 +68,12 @@ default DocumentPath getDocumentPath()
 
 	void setDisplayed(LogicExpressionResult displayed);
 
+	/**
+	 * Notify this instance that it's lookup values are staled. So next time they are needed, they need to be reloaded.
+	 * 
+	 * @param triggeringFieldName
+	 * @return
+	 */
 	boolean setLookupValuesStaled(String triggeringFieldName);
 
 	LookupValuesList getLookupValues();