DATAJDBC-432 - Extracted AggregateChangeExecutor from AggregateChange.

This separates the execution plan of  a change encoded in the AggregateChange from its execution encoded in the AggregateChangeExecutor.

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/AggregateChangeExecutor.java

@@ -0,0 +1,330 @@
+/*
+ * Copyright 2019 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.springframework.data.jdbc.core;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.BiConsumer;
+
+import org.springframework.data.mapping.PersistentProperty;
+import org.springframework.data.mapping.PersistentPropertyAccessor;
+import org.springframework.data.mapping.PersistentPropertyPath;
+import org.springframework.data.mapping.context.MappingContext;
+import org.springframework.data.relational.core.conversion.AggregateChange;
+import org.springframework.data.relational.core.conversion.DbAction;
+import org.springframework.data.relational.core.conversion.Interpreter;
+import org.springframework.data.relational.core.conversion.RelationalConverter;
+import org.springframework.data.relational.core.mapping.RelationalPersistentEntity;
+import org.springframework.data.relational.core.mapping.RelationalPersistentProperty;
+import org.springframework.data.util.Pair;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * Executes an {@link AggregateChange} by handing the included {@link DbAction} instances to the interpreter. In a
+ * second step ids generated by the {@link Interpreter} get propagated to the entities contained in the actions.
+ *
+ * @author Jens Schauder
+ * @author Mark Paluch
+ * @since 1.2
+ */
+class AggregateChangeExecutor {
+
+	private final Interpreter interpreter;
+	private final RelationalConverter converter;
+	private final MappingContext<? extends RelationalPersistentEntity<?>, ? extends RelationalPersistentProperty> context;
+
+	AggregateChangeExecutor(Interpreter interpreter, RelationalConverter converter) {
+
+		this.interpreter = interpreter;
+		this.converter = converter;
+		this.context = converter.getMappingContext();
+	}
+
+	@SuppressWarnings("unchecked")
+	<T> void execute(AggregateChange<T> aggregateChange) {
+
+		List<DbAction<?>> actions = new ArrayList<>();
+
+		aggregateChange.forEachAction(action -> {
+			action.executeWith(interpreter);
+			actions.add(action);
+		});
+
+		T newRoot = (T) populateIdsIfNecessary(actions);
+
+		if (newRoot != null) {
+			aggregateChange.setEntity(newRoot);
+		}
+	}
+
+	@Nullable
+	private Object populateIdsIfNecessary(List<DbAction<?>> actions) {
+
+		Object newRoot = null;
+
+		// have the actions so that the inserts on the leaves come first.
+		List<DbAction<?>> reverseActions = new ArrayList<>(actions);
+		Collections.reverse(reverseActions);
+
+		AggregateChangeExecutor.StagedValues cascadingValues = new AggregateChangeExecutor.StagedValues();
+
+		for (DbAction<?> action : reverseActions) {
+
+			if (!(action instanceof DbAction.WithGeneratedId)) {
+				continue;
+			}
+
+			DbAction.WithGeneratedId<?> withGeneratedId = (DbAction.WithGeneratedId<?>) action;
+			Object generatedId = withGeneratedId.getGeneratedId();
+			Object newEntity = setIdAndCascadingProperties(withGeneratedId, generatedId, cascadingValues);
+
+			// the id property was immutable so we have to propagate changes up the tree
+			if (newEntity != ((DbAction.WithGeneratedId<?>) action).getEntity()) {
+
+				if (action instanceof DbAction.Insert) {
+					DbAction.Insert insert = (DbAction.Insert) action;
+
+					Pair qualifier = insert.getQualifier();
+
+					cascadingValues.stage(insert.getDependingOn(), insert.getPropertyPath(),
+							qualifier == null ? null : qualifier.getSecond(), newEntity);
+
+				} else if (action instanceof DbAction.InsertRoot) {
+					newRoot = newEntity;
+				}
+			}
+		}
+
+		return newRoot;
+	}
+
+	@SuppressWarnings("unchecked")
+	private <S> Object setIdAndCascadingProperties(DbAction.WithGeneratedId<S> action, @Nullable Object generatedId,
+			AggregateChangeExecutor.StagedValues cascadingValues) {
+
+		S originalEntity = action.getEntity();
+
+		RelationalPersistentEntity<S> persistentEntity = (RelationalPersistentEntity<S>) context
+				.getRequiredPersistentEntity(action.getEntityType());
+		PersistentPropertyAccessor<S> propertyAccessor = converter.getPropertyAccessor(persistentEntity, originalEntity);
+
+		if (generatedId != null) {
+			propertyAccessor.setProperty(persistentEntity.getRequiredIdProperty(), generatedId);
+		}
+
+		// set values of changed immutables referenced by this entity
+		cascadingValues.forEachPath(action, (persistentPropertyPath, o) -> propertyAccessor
+				.setProperty(getRelativePath(action, persistentPropertyPath), o));
+
+		return propertyAccessor.getBean();
+	}
+
+	@SuppressWarnings("unchecked")
+	private PersistentPropertyPath getRelativePath(DbAction action, PersistentPropertyPath pathToValue) {
+
+		if (action instanceof DbAction.Insert) {
+			return pathToValue.getExtensionForBaseOf(((DbAction.Insert) action).getPropertyPath());
+		}
+
+		if (action instanceof DbAction.InsertRoot) {
+			return pathToValue;
+		}
+
+		throw new IllegalArgumentException(String.format("DbAction of type %s is not supported.", action.getClass()));
+	}
+
+	/**
+	 * Accumulates information about staged immutable objects in an aggregate that require updating because their state
+	 * changed because of {@link DbAction} execution.
+	 */
+	private static class StagedValues {
+
+		static final List<MultiValueAggregator> aggregators = Arrays.asList(SetAggregator.INSTANCE, MapAggregator.INSTANCE,
+				ListAggregator.INSTANCE, SingleElementAggregator.INSTANCE);
+
+		Map<DbAction, Map<PersistentPropertyPath, Object>> values = new HashMap<>();
+
+		/**
+		 * Adds a value that needs to be set in an entity higher up in the tree of entities in the aggregate. If the
+		 * attribute to be set is multivalued this method expects only a single element.
+		 *
+		 * @param action The action responsible for persisting the entity that needs the added value set. Must not be
+		 *          {@literal null}.
+		 * @param path The path to the property in which to set the value. Must not be {@literal null}.
+		 * @param qualifier If {@code path} is a qualified multivalued properties this parameter contains the qualifier. May
+		 *          be {@literal null}.
+		 * @param value The value to be set. Must not be {@literal null}.
+		 */
+		@SuppressWarnings("unchecked")
+		<T> void stage(DbAction<?> action, PersistentPropertyPath path, @Nullable Object qualifier, Object value) {
+
+			MultiValueAggregator<T> aggregator = getAggregatorFor(path);
+
+			Map<PersistentPropertyPath, Object> valuesForPath = this.values.computeIfAbsent(action,
+					dbAction -> new HashMap<>());
+
+			T currentValue = (T) valuesForPath.computeIfAbsent(path,
+					persistentPropertyPath -> aggregator.createEmptyInstance());
+
+			Object newValue = aggregator.add(currentValue, qualifier, value);
+
+			valuesForPath.put(path, newValue);
+		}
+
+		private MultiValueAggregator getAggregatorFor(PersistentPropertyPath path) {
+
+			PersistentProperty property = path.getRequiredLeafProperty();
+			for (MultiValueAggregator aggregator : aggregators) {
+				if (aggregator.handles(property)) {
+					return aggregator;
+				}
+			}
+
+			throw new IllegalStateException(String.format("Can't handle path %s", path));
+		}
+
+		/**
+		 * Performs the given action for each entry in this the staging area that are provided by {@link DbAction} until all
+		 * {@link PersistentPropertyPath} have been processed or the action throws an exception. The {@link BiConsumer
+		 * action} is called with each applicable {@link PersistentPropertyPath} and {@code value} that is assignable to the
+		 * property.
+		 */
+		void forEachPath(DbAction<?> dbAction, BiConsumer<PersistentPropertyPath, Object> action) {
+			values.getOrDefault(dbAction, Collections.emptyMap()).forEach(action);
+		}
+	}
+
+	interface MultiValueAggregator<T> {
+
+		default Class<? super T> handledType() {
+			return Object.class;
+		}
+
+		default boolean handles(PersistentProperty property) {
+			return handledType().isAssignableFrom(property.getType());
+		}
+
+		@Nullable
+		T createEmptyInstance();
+
+		T add(@Nullable T aggregate, @Nullable Object qualifier, Object value);
+
+	}
+
+	private enum SetAggregator implements MultiValueAggregator<Set> {
+
+		INSTANCE;
+
+		@Override
+		public Class<Set> handledType() {
+			return Set.class;
+		}
+
+		@Override
+		public Set createEmptyInstance() {
+			return new HashSet();
+		}
+
+		@SuppressWarnings("unchecked")
+		@Override
+		public Set add(@Nullable Set set, @Nullable Object qualifier, Object value) {
+
+			Assert.notNull(set, "Set must not be null");
+
+			set.add(value);
+			return set;
+		}
+	}
+
+	private enum ListAggregator implements MultiValueAggregator<List> {
+
+		INSTANCE;
+
+		@Override
+		public boolean handles(PersistentProperty property) {
+			return property.isCollectionLike();
+		}
+
+		@Override
+		public List createEmptyInstance() {
+			return new ArrayList();
+		}
+
+		@SuppressWarnings("unchecked")
+		@Override
+		public List add(@Nullable List list, @Nullable Object qualifier, Object value) {
+
+			Assert.notNull(list, "List must not be null.");
+
+			int index = (int) qualifier;
+			if (index >= list.size()) {
+				list.add(value);
+			} else {
+				list.add(index, value);
+			}
+
+			return list;
+		}
+	}
+
+	private enum MapAggregator implements MultiValueAggregator<Map> {
+
+		INSTANCE;
+
+		@Override
+		public Class<Map> handledType() {
+			return Map.class;
+		}
+
+		@Override
+		public Map createEmptyInstance() {
+			return new HashMap();
+		}
+
+		@SuppressWarnings("unchecked")
+		@Override
+		public Map add(@Nullable Map map, @Nullable Object qualifier, Object value) {
+
+			Assert.notNull(map, "Map must not be null.");
+
+			map.put(qualifier, value);
+			return map;
+		}
+	}
+
+	private enum SingleElementAggregator implements MultiValueAggregator<Object> {
+
+		INSTANCE;
+
+		@Override
+		@Nullable
+		public Object createEmptyInstance() {
+			return null;
+		}
+
+		@Override
+		public Object add(@Nullable Object __null, @Nullable Object qualifier, Object value) {
+			return value;
+		}
+	}
+}

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/JdbcAggregateTemplate.java

@@ -60,6 +60,7 @@ public class JdbcAggregateTemplate implements JdbcAggregateOperations {
 	private final RelationalEntityUpdateWriter jdbcEntityUpdateWriter;
 
 	private final DataAccessStrategy accessStrategy;
+	private final AggregateChangeExecutor executor;
 
 	private EntityCallbacks entityCallbacks = EntityCallbacks.create();
 
@@ -91,6 +92,8 @@ public class JdbcAggregateTemplate implements JdbcAggregateOperations {
 		this.jdbcEntityDeleteWriter = new RelationalEntityDeleteWriter(context);
 		this.interpreter = new DefaultJdbcInterpreter(context, accessStrategy);
 
+		this.executor = new AggregateChangeExecutor(interpreter, converter);
+
 		setEntityCallbacks(EntityCallbacks.create(publisher));
 	}
 
@@ -120,6 +123,8 @@ public class JdbcAggregateTemplate implements JdbcAggregateOperations {
 		this.jdbcEntityUpdateWriter = new RelationalEntityUpdateWriter(context);
 		this.jdbcEntityDeleteWriter = new RelationalEntityDeleteWriter(context);
 		this.interpreter = new DefaultJdbcInterpreter(context, accessStrategy);
+
+		this.executor = new AggregateChangeExecutor(interpreter, converter);
 	}
 
 	/**
@@ -292,7 +297,7 @@ public class JdbcAggregateTemplate implements JdbcAggregateOperations {
 		Assert.notNull(domainType, "Domain type must not be null!");
 
 		AggregateChange<?> change = createDeletingChange(domainType);
-		change.executeWith(interpreter, context, converter);
+		executor.execute(change);
 	}
 
 	private <T> T store(T aggregateRoot, Function<T, AggregateChange<T>> changeCreator,
@@ -309,7 +314,7 @@ public class JdbcAggregateTemplate implements JdbcAggregateOperations {
 
 		change.setEntity(aggregateRoot);
 
-		change.executeWith(interpreter, context, converter);
+		executor.execute(change);
 
 		Object identifier = persistentEntity.getIdentifierAccessor(change.getEntity()).getIdentifier();
 
@@ -325,7 +330,7 @@ public class JdbcAggregateTemplate implements JdbcAggregateOperations {
 		entity = triggerBeforeDelete(entity, id, change);
 		change.setEntity(entity);
 
-		change.executeWith(interpreter, context, converter);
+		executor.execute(change);
 
 		triggerAfterDelete(entity, id, change);
 	}

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/core/AggregateChangeIdGenerationImmutableUnitTests.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.springframework.data.relational.core.conversion;
+package org.springframework.data.jdbc.core;
 
 import static java.util.Arrays.*;
 import static java.util.Collections.*;
@@ -32,10 +32,14 @@ import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 import org.junit.Test;
-
 import org.springframework.data.annotation.Id;
 import org.springframework.data.mapping.PersistentPropertyPath;
 import org.springframework.data.mapping.PersistentPropertyPaths;
+import org.springframework.data.relational.core.conversion.AggregateChange;
+import org.springframework.data.relational.core.conversion.BasicRelationalConverter;
+import org.springframework.data.relational.core.conversion.DbAction;
+import org.springframework.data.relational.core.conversion.Interpreter;
+import org.springframework.data.relational.core.conversion.RelationalConverter;
 import org.springframework.data.relational.core.mapping.Embedded;
 import org.springframework.data.relational.core.mapping.RelationalMappingContext;
 import org.springframework.data.relational.core.mapping.RelationalPersistentProperty;
@@ -63,13 +67,15 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 	RelationalConverter converter = new BasicRelationalConverter(context);
 	DbAction.WithEntity<?> rootInsert = new DbAction.InsertRoot<>(entity);
 
+	AggregateChangeExecutor executor = new AggregateChangeExecutor(new IdSettingInterpreter(), converter);
+
 	@Test // DATAJDBC-291
 	public void singleRoot() {
 
 		AggregateChange<DummyEntity> aggregateChange = AggregateChange.forSave(entity);
 		aggregateChange.addAction(rootInsert);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -85,7 +91,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(rootInsert);
 		aggregateChange.addAction(createInsert("single", content, null));
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -106,7 +112,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(createInsert("contentList", content, 0));
 		aggregateChange.addAction(createInsert("contentList", content2, 1));
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -127,7 +133,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(createInsert("contentMap", content, "a"));
 		aggregateChange.addAction(createInsert("contentMap", content2, "b"));
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -149,7 +155,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(parentInsert);
 		aggregateChange.addAction(insert);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -174,7 +180,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(insert1);
 		aggregateChange.addAction(insert2);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -202,7 +208,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(insert1);
 		aggregateChange.addAction(insert2);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -238,7 +244,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(insert1);
 		aggregateChange.addAction(insert2);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -272,7 +278,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(insert2);
 		aggregateChange.addAction(insert3);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -309,7 +315,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(insert2);
 		aggregateChange.addAction(insert3);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -349,7 +355,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(insert1);
 		aggregateChange.addAction(insert2);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -374,7 +380,7 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 		aggregateChange.addAction(rootInsert);
 		aggregateChange.addAction(parentInsert);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		entity = aggregateChange.getEntity();
 
@@ -413,9 +419,10 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 
 	DbAction.Insert<?> createDeepInsert(String propertyName, Object value, Object key,
 			@Nullable DbAction.Insert<?> parentInsert) {
-
-		DbAction.Insert<Object> insert = new DbAction.Insert<>(value, toPath(entity, value), parentInsert);
-		insert.getQualifiers().put(toPath(parentInsert.getPropertyPath().toDotPath() + "." + propertyName), key);
+		PersistentPropertyPath<RelationalPersistentProperty> propertyPath = toPath(
+				parentInsert.getPropertyPath().toDotPath() + "." + propertyName);
+		DbAction.Insert<Object> insert = new DbAction.Insert<>(value, propertyPath, parentInsert);
+		insert.getQualifiers().put(propertyPath, key);
 		return insert;
 	}
 
@@ -428,14 +435,6 @@ public class AggregateChangeIdGenerationImmutableUnitTests {
 				.orElseThrow(() -> new IllegalArgumentException("No matching path found"));
 	}
 
-	PersistentPropertyPath<RelationalPersistentProperty> toPath(DummyEntity root, Object pathValue) {
-		// DefaultPersistentPropertyPath is package-public
-		return new WritingContext(context, entity, AggregateChange.forSave(root)).insert().stream()
-				.filter(a -> a instanceof DbAction.Insert).map(DbAction.Insert.class::cast)
-				.filter(a -> a.getEntity() == pathValue).map(DbAction.Insert::getPropertyPath).findFirst()
-				.orElseThrow(() -> new IllegalArgumentException("No matching path found for " + pathValue));
-	}
-
 	@Value
 	@Wither
 	@AllArgsConstructor

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/core/AggregateChangeIdGenerationUnitTests.java

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package org.springframework.data.relational.core.conversion;
+package org.springframework.data.jdbc.core;
 
 import static org.assertj.core.api.Assertions.*;
 
@@ -29,6 +29,11 @@ import org.junit.Test;
 import org.springframework.data.annotation.Id;
 import org.springframework.data.mapping.PersistentPropertyPath;
 import org.springframework.data.mapping.PersistentPropertyPaths;
+import org.springframework.data.relational.core.conversion.AggregateChange;
+import org.springframework.data.relational.core.conversion.BasicRelationalConverter;
+import org.springframework.data.relational.core.conversion.DbAction;
+import org.springframework.data.relational.core.conversion.Interpreter;
+import org.springframework.data.relational.core.conversion.RelationalConverter;
 import org.springframework.data.relational.core.mapping.RelationalMappingContext;
 import org.springframework.data.relational.core.mapping.RelationalPersistentProperty;
 import org.springframework.lang.Nullable;
@@ -52,13 +57,15 @@ public class AggregateChangeIdGenerationUnitTests {
 	RelationalConverter converter = new BasicRelationalConverter(context);
 	DbAction.WithEntity<?> rootInsert = new DbAction.InsertRoot<>(entity);
 
+	AggregateChangeExecutor executor = new AggregateChangeExecutor(new IdSettingInterpreter(), converter);
+
 	@Test // DATAJDBC-291
 	public void singleRoot() {
 
 		AggregateChange<DummyEntity> aggregateChange = AggregateChange.forSave(entity);
 		aggregateChange.addAction(rootInsert);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		assertThat(entity.rootId).isEqualTo(1);
 	}
@@ -72,7 +79,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(rootInsert);
 		aggregateChange.addAction(createInsert("single", content, null));
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		SoftAssertions.assertSoftly(softly -> {
 
@@ -92,7 +99,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(createInsert("contentList", content, 0));
 		aggregateChange.addAction(createInsert("contentList", content2, 1));
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		SoftAssertions.assertSoftly(softly -> {
 
@@ -112,7 +119,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(createInsert("contentMap", content, "a"));
 		aggregateChange.addAction(createInsert("contentMap", content2, "b"));
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		assertThat(entity.rootId).isEqualTo(1);
 		assertThat(entity.contentMap.values()).extracting(c -> c.id).containsExactly(2, 3);
@@ -132,7 +139,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(parentInsert);
 		aggregateChange.addAction(insert);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		assertThat(entity.rootId).isEqualTo(1);
 		assertThat(entity.single.id).isEqualTo(2);
@@ -156,7 +163,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(insert1);
 		aggregateChange.addAction(insert2);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		SoftAssertions.assertSoftly(softly -> {
 
@@ -183,7 +190,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(insert1);
 		aggregateChange.addAction(insert2);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		SoftAssertions.assertSoftly(softly -> {
 
@@ -218,7 +225,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(insert1);
 		aggregateChange.addAction(insert2);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		SoftAssertions.assertSoftly(softly -> {
 
@@ -252,7 +259,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(insert2);
 		aggregateChange.addAction(insert3);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		SoftAssertions.assertSoftly(softly -> {
 
@@ -290,7 +297,7 @@ public class AggregateChangeIdGenerationUnitTests {
 		aggregateChange.addAction(insert2);
 		aggregateChange.addAction(insert3);
 
-		aggregateChange.executeWith(new IdSettingInterpreter(), context, converter);
+		executor.execute(aggregateChange);
 
 		SoftAssertions.assertSoftly(softly -> {
 
@@ -321,8 +328,9 @@ public class AggregateChangeIdGenerationUnitTests {
 	DbAction.Insert<?> createDeepInsert(String propertyName, Object value, Object key,
 			@Nullable DbAction.Insert<?> parentInsert) {
 
-		DbAction.Insert<Object> insert = new DbAction.Insert<>(value, toPath(entity, value), parentInsert);
-		insert.getQualifiers().put(toPath(parentInsert.getPropertyPath().toDotPath() + "." + propertyName), key);
+		PersistentPropertyPath<RelationalPersistentProperty> propertyPath = toPath(parentInsert.getPropertyPath().toDotPath() + "." + propertyName);
+		DbAction.Insert<Object> insert = new DbAction.Insert<>(value, propertyPath, parentInsert);
+		insert.getQualifiers().put(propertyPath, key);
 		return insert;
 	}
 
@@ -335,14 +343,6 @@ public class AggregateChangeIdGenerationUnitTests {
 				.orElseThrow(() -> new IllegalArgumentException("No matching path found"));
 	}
 
-	PersistentPropertyPath<RelationalPersistentProperty> toPath(DummyEntity root, Object pathValue) {
-		// DefaultPersistentPropertyPath is package-public
-		return new WritingContext(context, entity, AggregateChange.forSave(root)).insert().stream()
-				.filter(a -> a instanceof DbAction.Insert).map(DbAction.Insert.class::cast)
-				.filter(a -> a.getEntity() == pathValue).map(DbAction.Insert::getPropertyPath).findFirst()
-				.orElseThrow(() -> new IllegalArgumentException("No matching path found"));
-	}
-
 	private static class DummyEntity {
 
 		@Id Integer rootId;

spring-data-relational/src/main/java/org/springframework/data/relational/core/conversion/AggregateChange.java

@@ -15,24 +15,10 @@
  */
 package org.springframework.data.relational.core.conversion;
 
-import lombok.Getter;
-
 import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.HashSet;
 import java.util.List;
-import java.util.Map;
-import java.util.Set;
-import java.util.function.BiConsumer;
+import java.util.function.Consumer;
 
-import org.springframework.data.mapping.PersistentProperty;
-import org.springframework.data.mapping.PersistentPropertyAccessor;
-import org.springframework.data.mapping.PersistentPropertyPath;
-import org.springframework.data.relational.core.mapping.RelationalMappingContext;
-import org.springframework.data.relational.core.mapping.RelationalPersistentEntity;
-import org.springframework.data.util.Pair;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -43,13 +29,13 @@ import org.springframework.util.ClassUtils;
  * @author Jens Schauder
  * @author Mark Paluch
  */
-@Getter
 public class AggregateChange<T> {
 
 	private final Kind kind;
 
 	/** Type of the aggregate root to be changed */
 	private final Class<T> entityType;
+
 	private final List<DbAction<?>> actions = new ArrayList<>();
 	/** Aggregate root, to which the change applies, if available */
 	@Nullable private T entity;
@@ -106,100 +92,84 @@ public class AggregateChange<T> {
 		return new AggregateChange<>(Kind.DELETE, entityClass, entity);
 	}
 
+	/**
+	 * Adds an action to this {@code AggregateChange}.
+	 * 
+	 * @param action must not be {@literal null}.
+	 */
+	public void addAction(DbAction<?> action) {
+
+		Assert.notNull(action, "Action must not be null.");
+
+		actions.add(action);
+	}
+
+	/**
+	 * Applies the given consumer to each {@link DbAction} in this {@code AggregateChange}.
+	 * 
+	 * @param consumer must not be {@literal null}.
+	 */
+	public void forEachAction(Consumer<? super DbAction<?>> consumer) {
+
+		Assert.notNull(consumer, "Consumer must not be null.");
+
+		actions.forEach(consumer);
+	}
+
+	/**
+	 * All the actions contained in this {@code AggregateChange}.
+	 * <p>
+	 * The behavior when modifying this list might result in undesired behavior.
+	 * <p>
+	 * Use {@link #addAction(DbAction)} to add actions.
+	 *
+	 * @return Guaranteed to be not {@literal null}.
+	 */
+	public List<DbAction<?>> getActions() {
+		return this.actions;
+	}
+
+	/**
+	 * Returns the {@link Kind} of {@code AggregateChange} this is.
+	 * 
+	 * @return guaranteed to be not {@literal null}.
+	 */
+	public Kind getKind() {
+		return this.kind;
+	}
+
+	/**
+	 * The type of the root of this {@code AggregateChange}.
+	 * 
+	 * @return Guaranteed to be not {@literal null}.
+	 */
+	public Class<T> getEntityType() {
+		return this.entityType;
+	}
+
+	/**
+	 * Set the root object of the {@code AggregateChange}.
+	 *
+	 * @param aggregateRoot may be {@literal null} if the change refers to a list of aggregates or references it by id.
+	 */
 	public void setEntity(@Nullable T aggregateRoot) {
-		// TODO: Check instanceOf compatibility to ensure type contract.
+
+		if (aggregateRoot != null) {
+			Assert.isInstanceOf(entityType, aggregateRoot,
+					String.format("AggregateRoot must be of type %s", entityType.getName()));
+		}
+
 		entity = aggregateRoot;
 	}
 
-	public void executeWith(Interpreter interpreter, RelationalMappingContext context, RelationalConverter converter) {
-
-		actions.forEach(action -> action.executeWith(interpreter));
-
-		T newRoot = populateIdsIfNecessary(context, converter);
-
-		if (newRoot != null) {
-			entity = newRoot;
-		}
-	}
-
+	/**
+	 * The entity to which this {@link AggregateChange} relates.
+	 * 
+	 * @return may be {@literal null}.
+	 */
 	@Nullable
-	private T populateIdsIfNecessary(RelationalMappingContext context, RelationalConverter converter) {
-
-		T newRoot = null;
-
-		// have the actions so that the inserts on the leaves come first.
-		ArrayList<DbAction<?>> reverseActions = new ArrayList<>(actions);
-		Collections.reverse(reverseActions);
-
-		StagedValues cascadingValues = new StagedValues();
-
-		for (DbAction<?> action : reverseActions) {
-
-			if (!(action instanceof DbAction.WithGeneratedId)) {
-				continue;
-			}
-
-			DbAction.WithGeneratedId<?> withGeneratedId = (DbAction.WithGeneratedId<?>) action;
-			Object generatedId = withGeneratedId.getGeneratedId();
-			Object newEntity = setIdAndCascadingProperties(context, converter, withGeneratedId, generatedId, cascadingValues);
-
-			// the id property was immutable so we have to propagate changes up the tree
-			if (newEntity != ((DbAction.WithGeneratedId<?>) action).getEntity()) {
-
-				if (action instanceof DbAction.Insert) {
-					DbAction.Insert insert = (DbAction.Insert) action;
-
-					Pair qualifier = insert.getQualifier();
-
-					cascadingValues.stage(insert.dependingOn, insert.propertyPath,
-							qualifier == null ? null : qualifier.getSecond(), newEntity);
-
-				} else if (action instanceof DbAction.InsertRoot) {
-					newRoot = entityType.cast(newEntity);
-				}
-			}
-		}
-
-		return newRoot;
-	}
-
-	@SuppressWarnings("unchecked")
-	private <S> Object setIdAndCascadingProperties(RelationalMappingContext context, RelationalConverter converter,
-			DbAction.WithGeneratedId<S> action, @Nullable Object generatedId, StagedValues cascadingValues) {
-
-		S originalEntity = action.getEntity();
-
-		RelationalPersistentEntity<S> persistentEntity = (RelationalPersistentEntity<S>) context
-				.getRequiredPersistentEntity(action.getEntityType());
-		PersistentPropertyAccessor<S> propertyAccessor = converter.getPropertyAccessor(persistentEntity, originalEntity);
-
-		if (generatedId != null) {
-			propertyAccessor.setProperty(persistentEntity.getRequiredIdProperty(), generatedId);
-		}
-
-		// set values of changed immutables referenced by this entity
-		cascadingValues.forEachPath(action, (persistentPropertyPath, o) -> propertyAccessor
-				.setProperty(getRelativePath(action, persistentPropertyPath), o));
-
-		return propertyAccessor.getBean();
-	}
-
-	@SuppressWarnings("unchecked")
-	private PersistentPropertyPath getRelativePath(DbAction action, PersistentPropertyPath pathToValue) {
-
-		if (action instanceof DbAction.Insert) {
-			return pathToValue.getExtensionForBaseOf(((DbAction.Insert) action).propertyPath);
-		}
-
-		if (action instanceof DbAction.InsertRoot) {
-			return pathToValue;
-		}
-
-		throw new IllegalArgumentException(String.format("DbAction of type %s is not supported.", action.getClass()));
-	}
-
-	public void addAction(DbAction<?> action) {
-		actions.add(action);
+	public T getEntity() {
+		return this.entity;
 	}
 
 	/**
@@ -218,182 +188,4 @@ public class AggregateChange<T> {
 		DELETE
 	}
 
-	/**
-	 * Accumulates information about staged immutable objects in an aggregate that require updating because their state
-	 * changed because of {@link DbAction} execution.
-	 */
-	private static class StagedValues {
-
-		static final List<MultiValueAggregator> aggregators = Arrays.asList(SetAggregator.INSTANCE, MapAggregator.INSTANCE,
-				ListAggregator.INSTANCE, SingleElementAggregator.INSTANCE);
-
-		Map<DbAction, Map<PersistentPropertyPath, Object>> values = new HashMap<>();
-
-		/**
-		 * Adds a value that needs to be set in an entity higher up in the tree of entities in the aggregate. If the
-		 * attribute to be set is multivalued this method expects only a single element.
-		 *
-		 * @param action The action responsible for persisting the entity that needs the added value set. Must not be
-		 *          {@literal null}.
-		 * @param path The path to the property in which to set the value. Must not be {@literal null}.
-		 * @param qualifier If {@code path} is a qualified multivalued properties this parameter contains the qualifier. May
-		 *          be {@literal null}.
-		 * @param value The value to be set. Must not be {@literal null}.
-		 */
-		@SuppressWarnings("unchecked")
-		<T> void stage(DbAction<?> action, PersistentPropertyPath path, @Nullable Object qualifier, Object value) {
-
-			MultiValueAggregator<T> aggregator = getAggregatorFor(path);
-
-			Map<PersistentPropertyPath, Object> valuesForPath = this.values.computeIfAbsent(action,
-					dbAction -> new HashMap<>());
-
-			T currentValue = (T) valuesForPath.computeIfAbsent(path,
-					persistentPropertyPath -> aggregator.createEmptyInstance());
-
-			Object newValue = aggregator.add(currentValue, qualifier, value);
-
-			valuesForPath.put(path, newValue);
-		}
-
-		private MultiValueAggregator getAggregatorFor(PersistentPropertyPath path) {
-
-			PersistentProperty property = path.getRequiredLeafProperty();
-			for (MultiValueAggregator aggregator : aggregators) {
-				if (aggregator.handles(property)) {
-					return aggregator;
-				}
-			}
-
-			throw new IllegalStateException(String.format("Can't handle path %s", path));
-		}
-
-		/**
-		 * Performs the given action for each entry in this the staging area that are provided by {@link DbAction} until all
-		 * {@link PersistentPropertyPath} have been processed or the action throws an exception. The {@link BiConsumer
-		 * action} is called with each applicable {@link PersistentPropertyPath} and {@code value} that is assignable to the
-		 * property.
-		 *
-		 * @param dbAction
-		 * @param action
-		 */
-		void forEachPath(DbAction<?> dbAction, BiConsumer<PersistentPropertyPath, Object> action) {
-			values.getOrDefault(dbAction, Collections.emptyMap()).forEach(action);
-		}
-	}
-
-	interface MultiValueAggregator<T> {
-
-		default Class<? super T> handledType() {
-			return Object.class;
-		}
-
-		default boolean handles(PersistentProperty property) {
-			return handledType().isAssignableFrom(property.getType());
-		}
-
-		@Nullable
-		T createEmptyInstance();
-
-		T add(@Nullable T aggregate, @Nullable Object qualifier, Object value);
-
-	}
-
-	private enum SetAggregator implements MultiValueAggregator<Set> {
-
-		INSTANCE;
-
-		@Override
-		public Class<Set> handledType() {
-			return Set.class;
-		}
-
-		@Override
-		public Set createEmptyInstance() {
-			return new HashSet();
-		}
-
-		@SuppressWarnings("unchecked")
-		@Override
-		public Set add(@Nullable Set set, @Nullable Object qualifier, Object value) {
-
-			Assert.notNull(set, "Set must not be null");
-
-			set.add(value);
-			return set;
-		}
-	}
-
-	private enum ListAggregator implements MultiValueAggregator<List> {
-
-		INSTANCE;
-
-		@Override
-		public boolean handles(PersistentProperty property) {
-			return property.isCollectionLike();
-		}
-
-		@Override
-		public List createEmptyInstance() {
-			return new ArrayList();
-		}
-
-		@SuppressWarnings("unchecked")
-		@Override
-		public List add(@Nullable List list, @Nullable Object qualifier, Object value) {
-
-			Assert.notNull(list, "List must not be null.");
-
-			int index = (int) qualifier;
-			if (index >= list.size()) {
-				list.add(value);
-			} else {
-				list.add(index, value);
-			}
-
-			return list;
-		}
-	}
-
-	private enum MapAggregator implements MultiValueAggregator<Map> {
-
-		INSTANCE;
-
-		@Override
-		public Class<Map> handledType() {
-			return Map.class;
-		}
-
-		@Override
-		public Map createEmptyInstance() {
-			return new HashMap();
-		}
-
-		@SuppressWarnings("unchecked")
-		@Override
-		public Map add(@Nullable Map map, @Nullable Object qualifier, Object value) {
-
-			Assert.notNull(map, "Map must not be null.");
-
-			map.put(qualifier, value);
-			return map;
-		}
-	}
-
-	private enum SingleElementAggregator implements MultiValueAggregator<Object> {
-
-		INSTANCE;
-
-		@Override
-		@Nullable
-		public Object createEmptyInstance() {
-			return null;
-		}
-
-		@Override
-		public Object add(@Nullable Object __null, @Nullable Object qualifier, Object value) {
-			return value;
-		}
-	}
-
 }