Properly handle associations in nested entities.

Nested entities that contain a reference to an aggregate root get a link to that attached to their representation. Previously, the creation of those links assumed that the reference is a materialized instance of the remote aggregate. That's now altered to be able to deal with associations, use identifiers directly or materialize to an intermediate aggregate instance to potentially use a custom lookup.

spring-data-rest-core/src/main/java/org/springframework/data/rest/core/mapping/PersistentPropertyResourceMapping.java

@@ -90,7 +90,7 @@ class PersistentPropertyResourceMapping implements PropertyAwareResourceMapping
 			return false;
 		}
 
-		ResourceMapping typeMapping = mappings.getMetadataFor(property.getActualType());
+		ResourceMapping typeMapping = mappings.getMetadataFor(property.getAssociationTargetType());
 		return !typeMapping.isExported() ? false : annotation.map(it -> it.exported()).orElse(true);
 	}
 

spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/DefaultSelfLinkProvider.java

@@ -17,9 +17,13 @@ package org.springframework.data.rest.core.support;
 
 import java.util.List;
 
+import org.springframework.core.convert.ConversionService;
+import org.springframework.data.mapping.PersistentEntity;
+import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.context.PersistentEntities;
 import org.springframework.hateoas.Link;
 import org.springframework.hateoas.server.EntityLinks;
+import org.springframework.lang.Nullable;
 import org.springframework.plugin.core.PluginRegistry;
 import org.springframework.util.Assert;
 
@@ -36,6 +40,7 @@ public class DefaultSelfLinkProvider implements SelfLinkProvider {
 	private final PersistentEntities entities;
 	private final EntityLinks entityLinks;
 	private final PluginRegistry<EntityLookup<?>, Class<?>> lookups;
+	private final ConversionService conversionService;
 
 	/**
 	 * Creates a new {@link DefaultSelfLinkProvider} from the {@link PersistentEntities}, {@link EntityLinks} and
@@ -46,7 +51,7 @@ public class DefaultSelfLinkProvider implements SelfLinkProvider {
 	 * @param lookups must not be {@literal null}.
 	 */
 	public DefaultSelfLinkProvider(PersistentEntities entities, EntityLinks entityLinks,
-			List<? extends EntityLookup<?>> lookups) {
+			List<? extends EntityLookup<?>> lookups, ConversionService conversionService) {
 
 		Assert.notNull(entities, "PersistentEntities must not be null!");
 		Assert.notNull(entityLinks, "EntityLinks must not be null!");
@@ -55,6 +60,7 @@ public class DefaultSelfLinkProvider implements SelfLinkProvider {
 		this.entities = entities;
 		this.entityLinks = entityLinks;
 		this.lookups = PluginRegistry.of(lookups);
+		this.conversionService = conversionService;
 	}
 
 	/*
@@ -65,29 +71,54 @@ public class DefaultSelfLinkProvider implements SelfLinkProvider {
 
 		Assert.notNull(instance, "Domain object must not be null!");
 
-		return entityLinks.linkToItemResource(instance.getClass(), getResourceId(instance));
+		return createSelfLinkFor(instance.getClass(), instance);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.rest.core.support.SelfLinkProvider#createSelfLinkFor(java.lang.Class, java.lang.Object)
+	 */
+	public Link createSelfLinkFor(Class<?> type, Object reference) {
+
+		if (type.isInstance(reference)) {
+			return entityLinks.linkToItemResource(type, getResourceId(type, reference));
+		}
+
+		PersistentEntity<?, ?> entity = entities.getRequiredPersistentEntity(type);
+		PersistentProperty<?> idProperty = entity.getRequiredIdProperty();
+
+		Object identifier = conversionService.convert(reference, idProperty.getType());
+
+		if (lookups.hasPluginFor(type)) {
+			identifier = getResourceId(type, conversionService.convert(identifier, type));
+		}
+
+		return entityLinks.linkToItemResource(type, identifier);
 	}
 
 	/**
 	 * Returns the identifier to be used to create the self link URI.
 	 *
-	 * @param instance must not be {@literal null}.
+	 * @param reference must not be {@literal null}.
 	 * @return
 	 */
-	@SuppressWarnings("unchecked")
-	private Object getResourceId(Object instance) {
+	@Nullable
+	private Object getResourceId(Class<?> type, Object reference) {
 
-		Class<? extends Object> instanceType = instance.getClass();
+		if (!lookups.hasPluginFor(type)) {
+			return entityIdentifierOrNull(reference);
+		}
 
-		return lookups.getPluginFor(instanceType)//
+		return lookups.getPluginFor(type)//
 				.map(it -> it.getClass().cast(it))//
-				.map(it -> it.getResourceIdentifier(instance))//
-				.orElseGet(() -> identifierOrNull(instance));
+				.map(it -> it.getResourceIdentifier(reference))//
+				.orElseGet(() -> entityIdentifierOrNull(reference));
 	}
 
-	private Object identifierOrNull(Object instance) {
+	private Object entityIdentifierOrNull(Object instance) {
 
-		return entities.getRequiredPersistentEntity(instance.getClass())//
-				.getIdentifierAccessor(instance).getIdentifier();
+		return entities.getRequiredPersistentEntity(instance.getClass()) //
+				.getIdentifierAccessor(instance) //
+				.getIdentifier();
 	}
 }

spring-data-rest-core/src/main/java/org/springframework/data/rest/core/support/SelfLinkProvider.java

@@ -27,10 +27,24 @@ import org.springframework.hateoas.Link;
 public interface SelfLinkProvider {
 
 	/**
-	 * Returns the self link for the given entity instance.
+	 * Returns the self link for the given entity instance. Only call this with an actual entity instance. Otherwise,
+	 * prefer {@link #createSelfLinkFor(Class, Object)}.
 	 *
 	 * @param instance must never be {@literal null}.
 	 * @return will never be {@literal null}.
+	 * @see #createSelfLinkFor(Class, Object)
 	 */
 	Link createSelfLinkFor(Object instance);
+
+	/**
+	 * Returns the self link for the entity of the given type and the given reference. The latter can be an instance of
+	 * the former, an identifier value of the former or anything that can be converted into an identifier in the first
+	 * place.
+	 *
+	 * @param type must not be {@literal null}.
+	 * @param reference must not be {@literal null}.
+	 * @return will never be {@literal null}.
+	 * @since 3.5
+	 */
+	Link createSelfLinkFor(Class<?> type, Object reference);
 }

spring-data-rest-core/src/test/java/org/springframework/data/rest/core/support/DefaultSelfLinkProviderUnitTests.java

@@ -28,7 +28,8 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
 import org.mockito.junit.MockitoJUnitRunner;
-
+import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.data.keyvalue.core.mapping.context.KeyValueMappingContext;
 import org.springframework.data.mapping.MappingException;
 import org.springframework.data.mapping.context.PersistentEntities;
@@ -51,6 +52,7 @@ public class DefaultSelfLinkProviderUnitTests {
 	@Mock EntityLinks entityLinks;
 	PersistentEntities entities;
 	List<EntityLookup<?>> lookups;
+	ConversionService conversionService;
 
 	@Before
 	public void setUp() {
@@ -69,22 +71,23 @@ public class DefaultSelfLinkProviderUnitTests {
 
 		this.entities = new PersistentEntities(Arrays.asList(context));
 		this.lookups = Collections.emptyList();
-		this.provider = new DefaultSelfLinkProvider(entities, entityLinks, lookups);
+		this.conversionService = new DefaultConversionService();
+		this.provider = new DefaultSelfLinkProvider(entities, entityLinks, lookups, conversionService);
 	}
 
 	@Test(expected = IllegalArgumentException.class) // DATAREST-724
 	public void rejectsNullEntities() {
-		new DefaultSelfLinkProvider(null, entityLinks, lookups);
+		new DefaultSelfLinkProvider(null, entityLinks, lookups, conversionService);
 	}
 
 	@Test(expected = IllegalArgumentException.class) // DATAREST-724
 	public void rejectsNullEntityLinks() {
-		new DefaultSelfLinkProvider(entities, null, lookups);
+		new DefaultSelfLinkProvider(entities, null, lookups, conversionService);
 	}
 
 	@Test(expected = IllegalArgumentException.class) // DATAREST-724
 	public void rejectsNullEntityLookups() {
-		new DefaultSelfLinkProvider(entities, entityLinks, null);
+		new DefaultSelfLinkProvider(entities, entityLinks, null, conversionService);
 	}
 
 	@Test // DATAREST-724
@@ -104,7 +107,8 @@ public class DefaultSelfLinkProviderUnitTests {
 		when(lookup.supports(Profile.class)).thenReturn(true);
 		when(lookup.getResourceIdentifier(any(Profile.class))).thenReturn("foo");
 
-		this.provider = new DefaultSelfLinkProvider(entities, entityLinks, Collections.singletonList(lookup));
+		this.provider = new DefaultSelfLinkProvider(entities, entityLinks, Collections.singletonList(lookup),
+				conversionService);
 
 		Link link = provider.createSelfLinkFor(new Profile("Name", "Type"));
 
@@ -114,7 +118,8 @@ public class DefaultSelfLinkProviderUnitTests {
 	@Test // DATAREST-724, DATAREST-1549
 	public void rejectsLinkCreationForUnknownEntity() {
 
-		assertThatExceptionOfType(MappingException.class).isThrownBy(() -> provider.createSelfLinkFor(new Object())) //
+		assertThatExceptionOfType(MappingException.class) //
+				.isThrownBy(() -> provider.createSelfLinkFor(new Object())) //
 				.withMessageContaining(Object.class.getName()) //
 				.withMessageContaining("Couldn't find PersistentEntity for");
 	}