Delete referenced object

assets/DependingClasses.drawio

@@ -0,0 +1,48 @@
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+    <mxGraphModel dx="1562" dy="845" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="850" pageHeight="1100" math="0" shadow="0">
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+        <mxCell id="1" parent="0" />
+        <mxCell id="hvzIIKVZ51MqT405g5E5-15" value="" style="rounded=0;whiteSpace=wrap;html=1;strokeColor=none;" vertex="1" parent="1">
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+          <mxGeometry x="20" y="20" width="60" height="80" as="geometry" />
+        </mxCell>
+        <mxCell id="hvzIIKVZ51MqT405g5E5-4" value="&lt;span style=&quot;font-weight: 400; text-wrap-mode: wrap;&quot;&gt;ArticleRepository&lt;/span&gt;" style="text;strokeColor=none;fillColor=none;html=1;fontSize=15;fontStyle=1;verticalAlign=middle;align=center;" vertex="1" parent="hvzIIKVZ51MqT405g5E5-5">
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+        </mxCell>
+        <mxCell id="hvzIIKVZ51MqT405g5E5-2" value="&lt;span style=&quot;font-weight: 400; text-wrap-mode: wrap;&quot;&gt;OrderRepository&lt;/span&gt;" style="text;strokeColor=none;fillColor=none;html=1;fontSize=15;fontStyle=1;verticalAlign=middle;align=center;" vertex="1" parent="hvzIIKVZ51MqT405g5E5-6">
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+        </mxCell>
+        <mxCell id="hvzIIKVZ51MqT405g5E5-7" value="&lt;font&gt;Order&lt;/font&gt;" style="rounded=0;whiteSpace=wrap;html=1;fontSize=15;fillColor=none;strokeColor=#D62125;strokeWidth=3;align=center;verticalAlign=middle;fontFamily=Helvetica;fontColor=default;" vertex="1" parent="1">
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+  </diagram>
+</mxfile>

docs/modules/ROOT/pages/features/lazies.adoc

@@ -25,12 +25,46 @@ import software.xdev.spring.data.eclipse.store.repository.lazy.SpringDataEclipse
 
 public class Owner extends Person
 {
-	private String address;
-
+	//...
 	private final Lazy<List<Pet>> pets = SpringDataEclipseStoreLazy.build(new ArrayList<>());
 	//...
 ----
 
+== FetchType.LAZY
+
+In Spring JPA, lazy loading is achieved by annotating a field or property with ``FetchType.LAZY``.
+This approach leverages JPA's built-in mechanisms to defer the retrieval of the related entity until it is accessed.
+
+In contrast, {product-name} takes a different approach.
+Instead of using annotations, you wrap the object intended to be loaded lazily in a ``Lazy``-wrapper.
+This wrapper encapsulates the object and ensures it is only loaded when needed.
+
+[source,java,title="JPA Example with lazy"]
+----
+import jakarta.persistence.OneToMany;
+
+public class Owner extends Person
+{
+	@OneToMany(fetch = FetchType.LAZY)
+	private final List<Pet> pets = new ArrayList<>();
+	//...
+----
+
+[source,java,title="https://github.com/xdev-software/spring-data-eclipse-store/tree/develop/spring-data-eclipse-store-demo/src/main/java/software/xdev/spring/data/eclipse/store/demo/complex/owner/Owner.java[Slightly changed example from complex demo]"]
+----
+package software.xdev.spring.data.eclipse.store.demo.complex.owner;
+//...
+import software.xdev.spring.data.eclipse.store.repository.lazy.SpringDataEclipseStoreLazy;
+
+public class Owner extends Person
+{
+	private final List<Lazy<Pet>> pets = new ArrayList<>();
+	//...
+----
+
+The ``Lazy``-wrapper makes lazy loading **explicit and flexible**, avoiding JPA-specific overhead and potential exceptions.
+But it introduces a custom, less-standardized approach that may increase boilerplate and requires developers to remember to use the wrapper, which could lead to errors if overlooked.
+
 == Repositories
 
 Entities in a repository are by default **not lazy**.

docs/modules/ROOT/pages/known-issues.adoc

@@ -29,3 +29,37 @@ This **should** handle most problems with the ClassLoader.
 Restarting the storage leads to a reloading of all entities and may take some time, yet circumvents the Restart ClassLoader Issue.
 
 The behavior can be configured through xref:configuration.adoc#context-close-shutdown-storage[Properties] and is implemented in the https://github.com/xdev-software/spring-data-eclipse-store/tree/develop/spring-data-eclipse-store/src/main/java/software/xdev/spring/data/eclipse/store/repository/config/EclipseStoreClientConfiguration.java[EclipseStoreClientConfiguration.java].
+
+== Multiple Repositories with related entities [[multi-repos-with-related-entities]]
+
+In SQL databases, relationships between entities are explicitly defined and enforced by the database system.
+This ensures that constraints, such as foreign keys, are consistently maintained.
+
+In contrast, relationships in a Java object graph are solely defined by the developer.
+If an object within the graph does not maintain a reference back to its parent or containing object, it has no inherent knowledge of that relationship.
+Consequently, finding such a relationship requires searching the entire object graph, which can be highly inefficient.
+
+image::DependingClasses.svg[Example structure with orders and articles]
+
+Example Scenario:
+Consider an *order object* that contains references to several *article objects*.
+In this case, determining which order contains a specific article is nearly impossible without traversing the entire object graph to locate it.
+This lack of direct reference contrasts sharply with the behavior of SQL databases.
+
+What Happens When an Article is Deleted?
+
+1. In an *SQL Database*: +
+Attempting to delete an article that is still referenced (e.g., by an order) would typically result in an exception. +
+The database enforces referential integrity, preventing the deletion of a referenced entity.
+
+2. In *{product-name}*: +
+Deleting an article from the article repository is allowed, even if it is still referenced elsewhere. +
+The system does not track or enforce such references.
+As a result:
+
+* The article is removed from the repository.
+* However, the order still retains its reference to the now-deleted article.
+* If the order is subsequently saved, the article is reintroduced into the repository.
+
+This behavior is fundamentally different from the strict relationship management seen in SQL databases.
+Developers must be aware of these differences to avoid unintended side effects in their applications.

spring-data-eclipse-store/src/main/java/software/xdev/spring/data/eclipse/store/repository/EclipseStoreStorage.java

@@ -289,7 +289,6 @@ public <T> void store(
 				final Collection<Object> entitiesAndPossiblyNonEntitiesToStore =
 					this.collectRootEntitiesToStore(
 						this.getEntityData(clazz),
-						clazz,
 						entitiesToStore);
 				entitiesAndPossiblyNonEntitiesToStore.addAll(nonEntitiesToStore);
 				if(LOG.isDebugEnabled())
@@ -312,7 +311,6 @@ public <T> void store(
 	 */
 	private <T, ID> Collection<Object> collectRootEntitiesToStore(
 		final EntityData<T, ID> entityData,
-		final Class<T> clazz,
 		final Iterable<T> entitiesToStore)
 	{
 		final Collection<Object> objectsToStore = new ArrayList<>();
@@ -337,6 +335,7 @@ public <T> void delete(final Class<T> clazz, final T entityToRemove)
 			{
 				final EntityData<T, ?> entityData = this.getEntityData(clazz);
 				this.storageManager.storeAll(entityData.removeEntityAndReturnObjectsToStore(entityToRemove));
+
 				if(LOG.isDebugEnabled())
 				{
 					LOG.debug("Deleted single entity of class {}.", clazz.getSimpleName());

spring-data-eclipse-store/src/main/java/software/xdev/spring/data/eclipse/store/repository/support/reposyncer/SimpleRepositorySynchronizer.java

@@ -50,7 +50,7 @@ public SimpleRepositorySynchronizer(final RootDataV2_4 root)
 						return;
 					}
 					final Class<Object> objectInGraphClass = (Class<Object>)objectInGraph.getClass();
-					EntityData<Object, Object> entityDataForCurrentObject =
+					final EntityData<Object, Object> entityDataForCurrentObject =
 						this.root.getEntityData(objectInGraphClass);
 					if(entityDataForCurrentObject != null
 						&& !entityDataForCurrentObject.containsEntity(objectInGraph))
@@ -62,6 +62,9 @@ public SimpleRepositorySynchronizer(final RootDataV2_4 root)
 			).buildObjectGraphTraverser();
 	}
 
+	/**
+	 * This method can take a huge amount of time. Must be watched closely.
+	 */
 	@Override
 	public Collection<EntityData<Object, Object>> syncAndReturnChangedObjectLists(final Object objectToStore)
 	{

spring-data-eclipse-store/src/test/java/software/xdev/spring/data/eclipse/store/integration/isolated/tests/deletion/DeletionTest.java

@@ -51,23 +51,68 @@ void deleteReferencedObject(
 		final ReferencingDaoObject referencingDaoObject = new ReferencingDaoObject(referencedObject);
 		referencingRepository.save(referencingDaoObject);
 
-		Assertions.assertEquals(1, TestUtil.iterableToList(referencingRepository.findAll()).size());
-		Assertions.assertEquals(1, TestUtil.iterableToList(referencedRepository.findAll()).size());
+		Assertions.assertEquals(1, referencingRepository.findAll().size());
+		Assertions.assertEquals(1, referencedRepository.findAll().size());
 
 		referencedRepository.delete(referencedObject);
 
 		TestUtil.doBeforeAndAfterRestartOfDatastore(
 			this.configuration,
 			() -> {
-				Assertions.assertTrue(TestUtil.iterableToList(referencedRepository.findAll()).isEmpty());
-				final List<ReferencingDaoObject> referencingDaoObjects =
-					TestUtil.iterableToList(referencingRepository.findAll());
+				Assertions.assertTrue(referencedRepository.findAll().isEmpty());
+				final List<ReferencingDaoObject> referencingDaoObjects = referencingRepository.findAll();
 				Assertions.assertEquals(1, referencingDaoObjects.size());
 				Assertions.assertNotNull(referencingDaoObjects.get(0).getValue());
 			}
 		);
 	}
 
+	@Test
+	void deleteUnreferencedObject(@Autowired final ReferencedRepository referencedRepository)
+	{
+		final ReferencedDaoObject referencedObject = new ReferencedDaoObject("someValue");
+		referencedRepository.save(referencedObject);
+
+		Assertions.assertEquals(1, referencedRepository.findAll().size());
+
+		referencedRepository.delete(referencedObject);
+
+		TestUtil.doBeforeAndAfterRestartOfDatastore(
+			this.configuration,
+			() -> {
+				Assertions.assertTrue(referencedRepository.findAll().isEmpty());
+			}
+		);
+	}
+
+	@Test
+	void deleteDoubleReferencedObject(
+		@Autowired final ReferencedRepository referencedRepository,
+		@Autowired final ReferencingRepository referencingRepository)
+	{
+		final ReferencedDaoObject referencedObject = new ReferencedDaoObject("someValue");
+		final ReferencingDaoObject referencingDaoObject1 = new ReferencingDaoObject(referencedObject);
+		final ReferencingDaoObject referencingDaoObject2 = new ReferencingDaoObject(referencedObject);
+		referencingRepository.save(referencingDaoObject1);
+		referencingRepository.save(referencingDaoObject2);
+
+		Assertions.assertEquals(2, referencingRepository.findAll().size());
+		Assertions.assertEquals(1, referencedRepository.findAll().size());
+
+		referencedRepository.delete(referencedObject);
+
+		TestUtil.doBeforeAndAfterRestartOfDatastore(
+			this.configuration,
+			() -> {
+				Assertions.assertTrue(referencedRepository.findAll().isEmpty());
+				final List<ReferencingDaoObject> referencingDaoObjects = referencingRepository.findAll();
+				Assertions.assertEquals(2, referencingDaoObjects.size());
+				Assertions.assertNotNull(referencingDaoObjects.get(0).getValue());
+				Assertions.assertNotNull(referencingDaoObjects.get(1).getValue());
+			}
+		);
+	}
+
 	@Test
 	void restoreDeletedReferencedObject(
 		@Autowired final ReferencedRepository referencedRepository,
@@ -84,8 +129,8 @@ void restoreDeletedReferencedObject(
 		TestUtil.doBeforeAndAfterRestartOfDatastore(
 			this.configuration,
 			() -> {
-				Assertions.assertEquals(1, TestUtil.iterableToList(referencingRepository.findAll()).size());
-				Assertions.assertEquals(1, TestUtil.iterableToList(referencedRepository.findAll()).size());
+				Assertions.assertEquals(1, referencingRepository.findAll().size());
+				Assertions.assertEquals(1, referencedRepository.findAll().size());
 			}
 		);
 	}