Add the type hint _class attribute to the index mapping.

src/main/java/org/springframework/data/elasticsearch/core/convert/MappingElasticsearchConverter.java

@@ -23,7 +23,6 @@
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
 import org.springframework.beans.BeansException;
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.context.ApplicationContext;
@@ -550,25 +549,25 @@ public void write(Object source, Document sink) {
 		}
 
 		Class<?> entityType = ClassUtils.getUserClass(source.getClass());
-		TypeInformation<? extends Object> type = ClassTypeInformation.from(entityType);
+		TypeInformation<? extends Object> typeInformation = ClassTypeInformation.from(entityType);
 
 		if (requiresTypeHint(entityType)) {
-			typeMapper.writeType(type, sink);
+			typeMapper.writeType(typeInformation, sink);
 		}
 
-		writeInternal(source, sink, type);
+		writeInternal(source, sink, typeInformation);
 	}
 
 	/**
 	 * Internal write conversion method which should be used for nested invocations.
 	 *
 	 * @param source
 	 * @param sink
-	 * @param typeHint
+	 * @param typeInformation
 	 */
 	@SuppressWarnings("unchecked")
 	protected void writeInternal(@Nullable Object source, Map<String, Object> sink,
-			@Nullable TypeInformation<?> typeHint) {
+			@Nullable TypeInformation<?> typeInformation) {
 
 		if (null == source) {
 			return;
@@ -594,7 +593,7 @@ protected void writeInternal(@Nullable Object source, Map<String, Object> sink,
 		}
 
 		ElasticsearchPersistentEntity<?> entity = mappingContext.getRequiredPersistentEntity(entityType);
-		addCustomTypeKeyIfNecessary(typeHint, source, sink);
+		addCustomTypeKeyIfNecessary(source, sink, typeInformation);
 		writeInternal(source, sink, entity);
 	}
 
@@ -603,7 +602,7 @@ protected void writeInternal(@Nullable Object source, Map<String, Object> sink,
 	 *
 	 * @param source
 	 * @param sink
-	 * @param typeHint
+	 * @param entity
 	 */
 	protected void writeInternal(@Nullable Object source, Map<String, Object> sink,
 			@Nullable ElasticsearchPersistentEntity<?> entity) {
@@ -725,7 +724,7 @@ protected void writeProperty(ElasticsearchPersistentProperty property, Object va
 		Map<String, Object> document = existingValue instanceof Map ? (Map<String, Object>) existingValue
 				: Document.create();
 
-		addCustomTypeKeyIfNecessary(ClassTypeInformation.from(property.getRawType()), value, document);
+		addCustomTypeKeyIfNecessary(value, document, ClassTypeInformation.from(property.getRawType()));
 		writeInternal(value, document, entity);
 		sink.set(property, document);
 	}
@@ -923,18 +922,18 @@ protected Object getWriteComplexValue(ElasticsearchPersistentProperty property,
 	// region helper methods
 
 	/**
-	 * Adds custom type information to the given {@link Map} if necessary. That is if the value is not the same as the one
-	 * given. This is usually the case if you store a subtype of the actual declared type of the property.
+	 * Adds custom typeInformation information to the given {@link Map} if necessary. That is if the value is not the same
+	 * as the one given. This is usually the case if you store a subtype of the actual declared typeInformation of the
+	 * property.
 	 *
-	 * @param type
-	 * @param value must not be {@literal null}.
+	 * @param source must not be {@literal null}.
 	 * @param sink must not be {@literal null}.
+	 * @param type
 	 */
-	protected void addCustomTypeKeyIfNecessary(@Nullable TypeInformation<?> type, Object value,
-			Map<String, Object> sink) {
+	protected void addCustomTypeKeyIfNecessary(Object source, Map<String, Object> sink, @Nullable TypeInformation<?> type) {
 
 		Class<?> reference = type != null ? type.getActualType().getType() : Object.class;
-		Class<?> valueType = ClassUtils.getUserClass(value.getClass());
+		Class<?> valueType = ClassUtils.getUserClass(source.getClass());
 
 		boolean notTheSameClass = !valueType.equals(reference);
 		if (notTheSameClass) {
@@ -948,7 +947,7 @@ protected void addCustomTypeKeyIfNecessary(@Nullable TypeInformation<?> type, Ob
 	 * @param type must not be {@literal null}.
 	 * @return {@literal true} if not a simple type, {@link Collection} or type with custom write target.
 	 */
-	private boolean requiresTypeHint(Class<?> type) {
+	public boolean requiresTypeHint(Class<?> type) {
 
 		return !isSimpleType(type) && !ClassUtils.isAssignable(Collection.class, type)
 				&& !conversions.hasCustomWriteTarget(type, Document.class);

src/main/java/org/springframework/data/elasticsearch/core/index/MappingBuilder.java

@@ -81,6 +81,8 @@ public class MappingBuilder {
 	private static final String COMPLETION_MAX_INPUT_LENGTH = "max_input_length";
 	private static final String COMPLETION_CONTEXTS = "contexts";
 
+	private static final String TYPEHINT_PROPERTY = "_class";
+
 	private static final String TYPE_DYNAMIC = "dynamic";
 	private static final String TYPE_VALUE_KEYWORD = "keyword";
 	private static final String TYPE_VALUE_GEO_POINT = "geo_point";
@@ -131,6 +133,14 @@ public String buildPropertyMapping(Class<?> clazz) throws MappingException {
 		}
 	}
 
+	private void writeTypeHintMapping(XContentBuilder builder) throws IOException {
+		builder.startObject(TYPEHINT_PROPERTY) //
+				.field(FIELD_PARAM_TYPE, TYPE_VALUE_KEYWORD) //
+				.field(FIELD_PARAM_INDEX, false) //
+				.field(FIELD_PARAM_DOC_VALUES, false) //
+				.endObject();
+	}
+
 	private void mapEntity(XContentBuilder builder, @Nullable ElasticsearchPersistentEntity<?> entity,
 			boolean isRootObject, String nestedObjectFieldName, boolean nestedOrObjectField, FieldType fieldType,
 			@Nullable Field parentFieldAnnotation, @Nullable DynamicMapping dynamicMapping) throws IOException {
@@ -162,6 +172,8 @@ private void mapEntity(XContentBuilder builder, @Nullable ElasticsearchPersisten
 
 		builder.startObject(FIELD_PROPERTIES);
 
+		writeTypeHintMapping(builder);
+
 		if (entity != null) {
 			entity.doWithProperties((PropertyHandler<ElasticsearchPersistentProperty>) property -> {
 				try {

src/test/java/org/springframework/data/elasticsearch/core/ReactiveIndexOperationsTest.java

@@ -31,7 +31,6 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-import org.skyscreamer.jsonassert.JSONCompareMode;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
@@ -257,7 +256,7 @@ void shouldCreateMappingForEntityFromProperties() {
 				.as(StepVerifier::create) //
 				.assertNext(document -> {
 					try {
-						assertEquals(expected, document.toJson(), JSONCompareMode.NON_EXTENSIBLE);
+						assertEquals(expected, document.toJson(), false);
 					} catch (JSONException e) {
 						fail("", e);
 					}
@@ -282,7 +281,7 @@ void shouldCreateMappingForEntityFromMappingAnnotation() {
 				.as(StepVerifier::create) //
 				.assertNext(document -> {
 					try {
-						assertEquals(expected, document.toJson(), JSONCompareMode.NON_EXTENSIBLE);
+						assertEquals(expected, document.toJson(), false);
 					} catch (JSONException e) {
 						fail("", e);
 					}
@@ -310,7 +309,7 @@ void shouldCreateMappingBoundEntity() {
 				.as(StepVerifier::create) //
 				.assertNext(document -> {
 					try {
-						assertEquals(expected, document.toJson(), JSONCompareMode.NON_EXTENSIBLE);
+						assertEquals(expected, document.toJson(), false);
 					} catch (JSONException e) {
 						fail("", e);
 					}
@@ -340,7 +339,7 @@ void shouldPutAndGetMapping() {
 				.as(StepVerifier::create) //
 				.assertNext(document -> {
 					try {
-						assertEquals(expected, document.toJson(), JSONCompareMode.NON_EXTENSIBLE);
+						assertEquals(expected, document.toJson(), false);
 					} catch (JSONException e) {
 						fail("", e);
 					}

src/test/java/org/springframework/data/elasticsearch/core/index/MappingBuilderUnitTests.java

@@ -37,9 +37,7 @@
 import java.util.Collection;
 import java.util.Date;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.Map;
-import java.util.Set;
 
 import org.elasticsearch.search.suggest.completion.context.ContextMapping;
 import org.json.JSONException;
@@ -420,7 +418,7 @@ public void shouldSetFieldMappingProperties() throws JSONException {
 		String mapping = getMappingBuilder().buildPropertyMapping(FieldMappingParameters.class);
 
 		// then
-		assertEquals(expected, mapping, true);
+		assertEquals(expected, mapping, false);
 	}
 
 	@Test
@@ -439,7 +437,7 @@ void shouldWriteDynamicMappingSettings() throws JSONException {
 
 		String mapping = getMappingBuilder().buildPropertyMapping(ConfigureDynamicMappingEntity.class);
 
-		assertEquals(expected, mapping, true);
+		assertEquals(expected, mapping, false);
 	}
 
 	@Test // DATAES-784
@@ -454,7 +452,7 @@ void shouldMapPropertyObjectsToFieldDefinition() throws JSONException {
 
 		String mapping = getMappingBuilder().buildPropertyMapping(ValueDoc.class);
 
-		assertEquals(expected, mapping, true);
+		assertEquals(expected, mapping, false);
 	}
 
 	@Test // DATAES-788
@@ -568,6 +566,54 @@ void shouldOnlyAllowDisabledPropertiesOnTypeObject() {
 				.isInstanceOf(MappingException.class);
 	}
 
+	@Test // #1711
+	@DisplayName("should write typeHint entries")
+	void shouldWriteTypeHintEntries() throws JSONException {
+
+		String expected = "{\n" + //
+				"  \"properties\": {\n" + //
+				"    \"_class\": {\n" + //
+				"      \"type\": \"keyword\",\n" + //
+				"      \"index\": false,\n" + //
+				"      \"doc_values\": false\n" + //
+				"    },\n" + //
+				"    \"id\": {\n" + //
+				"      \"type\": \"keyword\"\n" + //
+				"    },\n" + //
+				"    \"nestedEntity\": {\n" + //
+				"      \"type\": \"nested\",\n" + //
+				"      \"properties\": {\n" + //
+				"        \"_class\": {\n" + //
+				"          \"type\": \"keyword\",\n" + //
+				"          \"index\": false,\n" + //
+				"          \"doc_values\": false\n" + //
+				"        },\n" + //
+				"        \"nestedField\": {\n" + //
+				"          \"type\": \"text\"\n" + //
+				"        }\n" + //
+				"      }\n" + //
+				"    },\n" + //
+				"    \"objectEntity\": {\n" + //
+				"      \"type\": \"object\",\n" + //
+				"      \"properties\": {\n" + //
+				"        \"_class\": {\n" + //
+				"          \"type\": \"keyword\",\n" + //
+				"          \"index\": false,\n" + //
+				"          \"doc_values\": false\n" + //
+				"        },\n" + //
+				"        \"objectField\": {\n" + //
+				"          \"type\": \"text\"\n" + //
+				"        }\n" + //
+				"      }\n" + //
+				"    }\n" + //
+				"  }\n" + //
+				"}\n"; //
+
+		String mapping = getMappingBuilder().buildPropertyMapping(TypeHintEntity.class);
+
+		assertEquals(expected, mapping, false);
+	}
+
 	@Setter
 	@Getter
 	@NoArgsConstructor
@@ -862,21 +908,6 @@ static class GeoEntity {
 				orientation = GeoShapeField.Orientation.clockwise) private String shape2;
 	}
 
-	@Document(indexName = "test-index-user-mapping-builder")
-	static class User {
-		@Nullable @Id private String id;
-
-		@Field(type = FieldType.Nested, ignoreFields = { "users" }) private Set<Group> groups = new HashSet<>();
-	}
-
-	@Document(indexName = "test-index-group-mapping-builder")
-	static class Group {
-
-		@Nullable @Id String id;
-
-		@Field(type = FieldType.Nested, ignoreFields = { "groups" }) private Set<User> users = new HashSet<>();
-	}
-
 	@Document(indexName = "test-index-field-mapping-parameters")
 	static class FieldMappingParameters {
 		@Nullable @Field private String indexTrue;
@@ -1008,4 +1039,25 @@ static class DisabledMappingProperty {
 		@Field(type = Text) private String text;
 		@Mapping(enabled = false) @Field(type = Object) private Object object;
 	}
+
+	@Data
+	@AllArgsConstructor
+	@NoArgsConstructor
+	static class TypeHintEntity {
+		@Id @Field(type = Keyword) private String id;
+
+		@Field(type = Nested) private NestedEntity nestedEntity;
+
+		@Field(type = Object) private ObjectEntity objectEntity;
+
+		@Data
+		static class NestedEntity {
+			@Field(type = Text) private String nestedField;
+		}
+
+		@Data
+		static class ObjectEntity {
+			@Field(type = Text) private String objectField;
+		}
+	}
 }

src/test/java/org/springframework/data/elasticsearch/core/index/SimpleDynamicTemplatesMappingTests.java

@@ -15,11 +15,12 @@
  */
 package org.springframework.data.elasticsearch.core.index;
 
-import static org.assertj.core.api.Assertions.*;
+import static org.skyscreamer.jsonassert.JSONAssert.*;
 
 import java.util.HashMap;
 import java.util.Map;
 
+import org.json.JSONException;
 import org.junit.jupiter.api.Test;
 import org.springframework.data.annotation.Id;
 import org.springframework.data.elasticsearch.annotations.Document;
@@ -38,19 +39,19 @@
 public class SimpleDynamicTemplatesMappingTests extends MappingContextBaseTests {
 
 	@Test // DATAES-568
-	public void testCorrectDynamicTemplatesMappings() {
+	public void testCorrectDynamicTemplatesMappings() throws JSONException {
 
 		String mapping = getMappingBuilder().buildPropertyMapping(SampleDynamicTemplatesEntity.class);
 
 		String EXPECTED_MAPPING_ONE = "{\"dynamic_templates\":" + "[{\"with_custom_analyzer\":{"
 				+ "\"mapping\":{\"type\":\"string\",\"analyzer\":\"standard_lowercase_asciifolding\"},"
 				+ "\"path_match\":\"names.*\"}}]," + "\"properties\":{\"names\":{\"type\":\"object\"}}}";
 
-		assertThat(mapping).isEqualTo(EXPECTED_MAPPING_ONE);
+		assertEquals(EXPECTED_MAPPING_ONE, mapping, false);
 	}
 
 	@Test // DATAES-568
-	public void testCorrectDynamicTemplatesMappingsTwo() {
+	public void testCorrectDynamicTemplatesMappingsTwo() throws JSONException {
 
 		String mapping = getMappingBuilder().buildPropertyMapping(SampleDynamicTemplatesEntityTwo.class);
 		String EXPECTED_MAPPING_TWO = "{\"dynamic_templates\":" + "[{\"with_custom_analyzer\":{"
@@ -59,7 +60,7 @@ public void testCorrectDynamicTemplatesMappingsTwo() {
 				+ "\"mapping\":{\"type\":\"string\",\"analyzer\":\"standard_lowercase_asciifolding\"},"
 				+ "\"path_match\":\"participantA1.*\"}}]," + "\"properties\":{\"names\":{\"type\":\"object\"}}}";
 
-		assertThat(mapping).isEqualTo(EXPECTED_MAPPING_TWO);
+		assertEquals(EXPECTED_MAPPING_TWO, mapping, false);
 	}
 
 	/**

src/test/java/org/springframework/data/elasticsearch/core/index/SimpleElasticsearchDateMappingTests.java

@@ -15,13 +15,14 @@
  */
 package org.springframework.data.elasticsearch.core.index;
 
-import static org.assertj.core.api.Assertions.*;
+import static org.skyscreamer.jsonassert.JSONAssert.*;
 import static org.springframework.data.elasticsearch.annotations.FieldType.*;
 
 import lombok.Data;
 
 import java.time.LocalDateTime;
 
+import org.json.JSONException;
 import org.junit.jupiter.api.Test;
 import org.springframework.data.annotation.Id;
 import org.springframework.data.elasticsearch.annotations.DateFormat;
@@ -43,11 +44,11 @@ public class SimpleElasticsearchDateMappingTests extends MappingContextBaseTests
 			+ "\"basicFormatDate\":{\"" + "type\":\"date\",\"format\":\"basic_date\"}}}";
 
 	@Test // DATAES-568, DATAES-828
-	public void testCorrectDateMappings() {
+	public void testCorrectDateMappings() throws JSONException {
 
 		String mapping = getMappingBuilder().buildPropertyMapping(SampleDateMappingEntity.class);
 
-		assertThat(mapping).isEqualTo(EXPECTED_MAPPING);
+		assertEquals(EXPECTED_MAPPING, mapping, false);
 	}
 
 	/**