Remove the notion of “state-neutral” events.

Author: alexander-yevsyukov

server/src/main/java/org/spine3/server/aggregate/Aggregate.java

@@ -45,14 +45,10 @@
 import javax.annotation.CheckReturnValue;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
-import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
-import java.util.Set;
 
 import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Throwables.propagate;
-import static com.google.common.collect.Collections2.filter;
 import static org.spine3.base.Identifiers.idToAny;
 
 //TODO:2016-02-17:alexander.yevsyukov: Define syntax of event applier methods.
@@ -307,22 +303,16 @@ public void play(Iterable<Event> events) {
      * @param messages the event message to apply
      * @param commandContext the context of the command, execution of which produces the passed events
      * @throws InvocationTargetException if an exception occurs during event applying
-     * @see #getStateNeutralEventClasses()
      */
     private void apply(Iterable<? extends Message> messages, CommandContext commandContext) throws InvocationTargetException {
-        final Set<Class<? extends Message>> stateNeutralEventClasses = getStateNeutralEventClasses();
 
         //TODO:2016-03-24:alexander.yevsyukov: Init the builder of the state. Add getBuilder() method.
         // Assume that the code of event appliers would call getBuilder() instead of getState().
         // Throw IllegalStateException in the getBuilder() method if it's called from other stages of
         // the aggregate lifecycle.
 
         for (Message message : messages) {
-            final boolean isStateNeutral = stateNeutralEventClasses.contains(message.getClass());
-            if (!isStateNeutral) {
-                apply(message);
-            }
-            //TODO:2016-03-24:alexander.yevsyukov: increment version
+            apply(message);
 
             final int currentVersion = getVersion();
             final M state = getState();
@@ -331,7 +321,6 @@ private void apply(Iterable<? extends Message> messages, CommandContext commandC
             putUncommitted(event);
         }
 
-        //TODO:2016-03-24:alexander.yevsyukov: set new date/time
 
         //TODO:2016-03-24:alexander.yevsyukov: set new state
         //TODO:2016-03-24:alexander.yevsyukov: Clean builder.
@@ -353,30 +342,9 @@ private void apply(Message eventMessage) throws InvocationTargetException {
             return;
         }
         invokeApplier(eventMessage);
-    }
 
-    /**
-     * Returns a set of classes of state-neutral events (an empty set by default).
-     *
-     * <p>An event is state-neutral if we do not modify the aggregate state when this event occurs.
-     *
-     * <p>Instead of creating empty applier methods for such events,
-     * override this method returning immutable set of event classes. For example:
-     *
-     * <pre>
-     * private static final ImmutableSet&lt;Class&lt;? extends Message&gt;&gt; STATE_NEUTRAL_EVENT_CLASSES =
-     *         ImmutableSet.&lt;Class&lt;? extends Message&gt;&gt;of(StateNeutralEvent.class);
-     *
-     * &#64;Override
-     * protected Set&lt;Class&lt;? extends Message&gt;&gt; getStateNeutralEventClasses() {
-     *     return STATE_NEUTRAL_EVENT_CLASSES;
-     * }
-     * </pre>
-     *
-     * @return a set of classes of state-neutral events
-     */
-    protected Set<Class<? extends Message>> getStateNeutralEventClasses() {
-        return Collections.emptySet();
+        //TODO:2016-03-24:alexander.yevsyukov: increment version
+        //TODO:2016-03-24:alexander.yevsyukov: set new date/time
     }
 
     /**
@@ -395,54 +363,15 @@ private void putUncommitted(Event record) {
     }
 
     /**
-     * Returns all uncommitted events (including state-neutral).
+     * Returns all uncommitted events.
      *
      * @return immutable view of records for all uncommitted events
-     * @see #getStateNeutralEventClasses()
      */
     @CheckReturnValue
     public List<Event> getUncommittedEvents() {
         return ImmutableList.copyOf(uncommittedEvents);
     }
 
-    /**
-     * Returns uncommitted events (excluding state-neutral).
-     *
-     * @return an immutable view of records for applicable uncommitted events
-     * @see #getStateNeutralEventClasses()
-     */
-    @SuppressWarnings("InstanceMethodNamingConvention") // Prefer longer name here for clarity.
-    protected Collection<Event> getStateChangingUncommittedEvents() {
-        final Predicate<Event> isStateChanging = isStateChangingEventRecord();
-        final Collection<Event> result = filter(uncommittedEvents, isStateChanging);
-        return result;
-    }
-
-    /**
-     * Creates the predicate that filters {@code EventRecord}s which modify the state
-     * of the aggregate.
-     *
-     * <p>The predicate uses passed event classes for the events that do not modify the
-     * state of the aggregate. As such, they are called <em>State Neutral.</em>
-     *
-     * @return new predicate instance
-     */
-    private Predicate<Event> isStateChangingEventRecord() {
-        final Collection<Class<? extends Message>> stateNeutralEventClasses = getStateNeutralEventClasses();
-        return new Predicate<Event>() {
-            @Override
-            public boolean apply(
-                    @SuppressWarnings("NullableProblems")
-                    /* The @Nullable annotation is removed to avoid checking for null input,
-                       which is not possible here. Having the null input doesn't allow to test
-                       that code branch. */ Event event) {
-                final Message message = Events.getMessage(event);
-                final boolean isStateNeutral = stateNeutralEventClasses.contains(message.getClass());
-                return !isStateNeutral;
-            }
-        };
-    }
-
     /**
      * Returns and clears all the events that were uncommitted before the call of this method.
      *

server/src/main/java/org/spine3/server/aggregate/AggregateRepository.java

@@ -175,7 +175,7 @@ public A load(I id) throws IllegalStateException {
      */
     @Override
     public void store(A aggregate) {
-        final Iterable<Event> uncommittedEvents = aggregate.getStateChangingUncommittedEvents();
+        final Iterable<Event> uncommittedEvents = aggregate.getUncommittedEvents();
 
         //TODO:2016-01-22:alexander.yevsyukov: The below code is not correct.
         // Now we're storing snapshot in a sequence of uncommitted

server/src/main/java/org/spine3/server/aggregate/Apply.java

@@ -20,13 +20,13 @@
 
 package org.spine3.server.aggregate;
 
-import com.google.protobuf.Message;
-
 import java.lang.annotation.ElementType;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 
+//TODO:2016-03-24:alexander.yevsyukov: Update with description of new applier convention: getBuilder(), etc.
+
 /**
  * Marks a method of an aggregate as one that modifies the state of the aggregate with data from the passed event.
 
@@ -37,13 +37,6 @@
  *
  * <p>The type of the event will be indicated by the first (and only) parameter.
  *
- * <p>Event applier should call {@link Aggregate#incrementState(Message)},
- * which will advance the version and record the time of the modification.
- *
- * <p>It may turn that the event is state-neutral.
- * An event is state-neutral if we do not modify the aggregate state when this event occurs.
- * Please see {@link Aggregate#getStateNeutralEventClasses()} for more details and a sample.
- *
  * @author Alexander Yevsyukov
  */
 @Retention(RetentionPolicy.RUNTIME)

server/src/test/java/org/spine3/server/aggregate/AggregateShould.java

@@ -23,7 +23,6 @@
 import com.google.common.base.Function;
 import com.google.common.base.Throwables;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.ImmutableSet;
 import com.google.protobuf.Message;
 import com.google.protobuf.Timestamp;
 import org.junit.Before;
@@ -202,19 +201,6 @@ public void throw_exception_if_missing_event_applier_for_non_state_neutral_event
         }
     }
 
-    @Test
-    public void not_throw_exception_if_missing_event_applier_for_state_neutral_event() {
-        final TestAggregateWithStateNeutralEvents aggregate = new TestAggregateWithStateNeutralEvents(ID);
-        try {
-            aggregate.testDispatch(addTask, COMMAND_CONTEXT);
-            assertTrue(aggregate.isTaskAddedCommandHandled);
-        } catch (IllegalStateException e) {
-            fail("Method must not throw 'missing event applier exception' because this event is state neutral and " +
-                    "the applier is not required.");
-            throw e;
-        }
-    }
-
     @Test
     public void return_command_classes_which_are_handled_by_aggregate() {
         final Set<Class<? extends Message>> classes = Aggregate.getCommandClasses(TestAggregate.class);
@@ -316,16 +302,6 @@ public void return_uncommitted_event_records_after_dispatch() {
                 ProjectCreated.class, TaskAdded.class, ProjectStarted.class);
     }
 
-    @Test
-    public void return_only_state_changing_uncommitted_event_records_after_dispatch() {
-        final TestAggregateWithStateNeutralEvents aggregate = new TestAggregateWithStateNeutralEvents(ID);
-
-        aggregate.dispatchCommands(createProject, addTask);
-
-        final Collection<Event> events = aggregate.getStateChangingUncommittedEvents();
-        assertContains(eventsToClasses(events), ProjectCreated.class);
-    }
-
     @Test
     public void not_return_any_event_records_when_commit_by_default() {
         final List<Event> events = aggregate.commitEvents();
@@ -517,52 +493,6 @@ public ProjectCreated handle(CreateProject cmd, CommandContext ctx) {
         }
     }
 
-    /*
-     * Class only for test case: applier is not required for state-neutral event.
-     */
-    private static class TestAggregateWithStateNeutralEvents extends Aggregate<ProjectId, Project> {
-
-        private static final ImmutableSet<Class<? extends Message>> STATE_NEUTRAL_EVENT_CLASSES =
-                ImmutableSet.<Class<? extends Message>>of(TaskAdded.class);
-
-        private boolean isTaskAddedCommandHandled = false;
-
-        public TestAggregateWithStateNeutralEvents(ProjectId id) {
-            super(id);
-        }
-
-        @Assign
-        public ProjectCreated handle(CreateProject cmd, CommandContext ctx) {
-            return projectCreatedEvent(cmd.getProjectId());
-        }
-
-        @Apply
-        private void event(ProjectCreated event) {
-        }
-
-        /**
-         * There is no event applier for TaskAdded event because this event is state-neutral.
-         */
-        @Assign
-        public TaskAdded handle(AddTask cmd, CommandContext ctx) {
-            isTaskAddedCommandHandled = true;
-            return taskAddedEvent(cmd.getProjectId());
-        }
-
-        @Override
-        @SuppressWarnings({"RefusedBequest", // OK as the default implementation returns empty set.
-                           "ReturnOfCollectionOrArrayField"}) // OK, as we return immutable implementation.
-        protected Set<Class<? extends Message>> getStateNeutralEventClasses() {
-            return STATE_NEUTRAL_EVENT_CLASSES;
-        }
-
-        public void dispatchCommands(Message... commands) {
-            for (Message cmd : commands) {
-                testDispatch(cmd, COMMAND_CONTEXT);
-            }
-        }
-    }
-
     private static class TestAggregateWithIdString extends Aggregate<String, Project> {
         private TestAggregateWithIdString(String id) {
             super(id);