GH-1926 - Avoid wrapping nested entities ultimately to represent a value.

NestedEntitySerializer now skips the wrapping into an EntityModel if the target serializer is a JsonValueSerializer as EntityModel requires the value to ultimately resolve into key value pairs as it's only enriching something that's rendered as JSON document with hypermedia elements.

spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2Module.java

@@ -89,6 +89,7 @@ import com.fasterxml.jackson.databind.jsontype.TypeSerializer;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;
 import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
+import com.fasterxml.jackson.databind.ser.std.JsonValueSerializer;
 import com.fasterxml.jackson.databind.ser.std.StdScalarSerializer;
 import com.fasterxml.jackson.databind.ser.std.StdSerializer;
 import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
@@ -354,7 +355,7 @@ public class PersistentEntityJackson2Module extends SimpleModule {
 				List<Object> resources = new ArrayList<Object>();
 
 				for (Object element : source) {
-					resources.add(toModel(element));
+					resources.add(toModel(element, provider));
 				}
 
 				provider.defaultSerializeValue(resources, gen);
@@ -365,13 +366,13 @@ public class PersistentEntityJackson2Module extends SimpleModule {
 				Map<Object, Object> resources = CollectionFactory.createApproximateMap(value.getClass(), source.size());
 
 				for (Entry<?, ?> entry : source.entrySet()) {
-					resources.put(entry.getKey(), toModel(entry.getValue()));
+					resources.put(entry.getKey(), toModel(entry.getValue(), provider));
 				}
 
 				provider.defaultSerializeValue(resources, gen);
 
 			} else {
-				provider.defaultSerializeValue(toModel(value), gen);
+				provider.defaultSerializeValue(toModel(value, provider), gen);
 			}
 		}
 
@@ -385,7 +386,13 @@ public class PersistentEntityJackson2Module extends SimpleModule {
 			serialize(value, gen, provider);
 		}
 
-		private EntityModel<Object> toModel(Object value) {
+		private Object toModel(Object value, SerializerProvider provider) throws JsonMappingException {
+
+			JsonSerializer<Object> serializer = provider.findValueSerializer(value.getClass());
+
+			if (JsonValueSerializer.class.isInstance(serializer)) {
+				return value;
+			}
 
 			PersistentEntity<?, ?> entity = entities.getRequiredPersistentEntity(value.getClass());
 

spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2ModuleUnitTests.java

@@ -19,6 +19,7 @@ import static org.assertj.core.api.Assertions.*;
 import static org.mockito.ArgumentMatchers.*;
 import static org.mockito.Mockito.*;
 
+import lombok.Data;
 import lombok.Getter;
 
 import java.io.IOException;
@@ -58,6 +59,7 @@ import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonInclude.Include;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import com.fasterxml.jackson.annotation.JsonValue;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 import com.jayway.jsonpath.JsonPath;
@@ -89,6 +91,7 @@ public class PersistentEntityJackson2ModuleUnitTests {
 		mappingContext.getPersistentEntity(SampleWithAdditionalGetters.class);
 		mappingContext.getPersistentEntity(PersistentEntityJackson2ModuleUnitTests.PetOwner.class);
 		mappingContext.getPersistentEntity(Immutable.class);
+		mappingContext.getPersistentEntity(Wrapper.class);
 
 		this.persistentEntities = new PersistentEntities(Arrays.asList(mappingContext));
 
@@ -197,6 +200,16 @@ public class PersistentEntityJackson2ModuleUnitTests {
 				TypeDescriptor.valueOf(Home.class));
 	}
 
+	@Test // GH-1926
+	public void doesNotWrapJsonValueTypesIntoEntityModel() throws Exception {
+
+		Wrapper wrapper = new Wrapper();
+		wrapper.value = new ValueType();
+		wrapper.value.value = "sample";
+
+		assertThat(mapper.writeValueAsString(wrapper)).isEqualTo("{\"value\":\"sample\"}");
+	}
+
 	/**
 	 * @author Oliver Gierke
 	 */
@@ -257,4 +270,15 @@ public class PersistentEntityJackson2ModuleUnitTests {
 			this.home = home;
 		}
 	}
+
+	// GH-1926
+
+	@Data
+	static class Wrapper {
+		ValueType value;
+	}
+
+	static class ValueType {
+		@JsonValue String value;
+	}
 }