Add support for field aliases in the index mapping.

Original Pull Request #2847
Closes #2845

src/main/antora/modules/ROOT/pages/elasticsearch/elasticsearch-new.adoc

@@ -9,6 +9,7 @@
 * Add shard statistics to the `SearchHit` class.
 * Add support for multi search template API.
 * Add support for SpEL in @Query.
+* Add support for field aliases in the index mapping.
 
 [[new-features.5-2-0]]
 == New in Spring Data Elasticsearch 5.2

src/main/java/org/springframework/data/elasticsearch/annotations/Mapping.java

@@ -74,6 +74,13 @@ public @interface Mapping {
 	 */
 	String runtimeFieldsPath() default "";
 
+	/**
+	 * field alias definitions to be written to the index mapping
+	 *
+	 * @since 5.3
+	 */
+	MappingAlias[] aliases() default {};
+
 	enum Detection {
 		DEFAULT, TRUE, FALSE;
 	}

src/main/java/org/springframework/data/elasticsearch/annotations/MappingAlias.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2024 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.elasticsearch.annotations;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Defines a field alias in the index mapping.
+ *
+ * @author Peter-Josef Meisch
+ * @since 5.3
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.FIELD)
+@Documented
+@Inherited
+public @interface MappingAlias {
+	/**
+	 * the name of the alias.
+	 */
+	String name();
+
+	/**
+	 * the path of the alias.
+	 */
+	String path();
+}

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

@@ -214,8 +214,9 @@ public class MappingBuilder {
 				@Nullable Field parentFieldAnnotation, @Nullable Dynamic dynamicMapping, @Nullable Document runtimeFields)
 				throws IOException {
 
-			if (entity != null && entity.isAnnotationPresent(Mapping.class)) {
-				Mapping mappingAnnotation = entity.getRequiredAnnotation(Mapping.class);
+			var mappingAnnotation = entity != null ? entity.findAnnotation(Mapping.class) : null;
+
+			if (mappingAnnotation != null) {
 
 				if (!mappingAnnotation.enabled()) {
 					objectNode.put(MAPPING_ENABLED, false);
@@ -289,6 +290,16 @@ public class MappingBuilder {
 						LOGGER.warn(String.format("error mapping property with name %s", property.getName()), e);
 					}
 				});
+
+			}
+
+			// write the alias entries after the properties
+			if (mappingAnnotation != null) {
+				for (MappingAlias mappingAlias : mappingAnnotation.aliases()) {
+					var aliasNode = propertiesNode.putObject(mappingAlias.name());
+					aliasNode.put(FIELD_PARAM_TYPE, FIELD_PARAM_TYPE_ALIAS);
+					aliasNode.put(FIELD_PARAM_PATH, mappingAlias.path());
+				}
 			}
 		}
 

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

@@ -84,6 +84,8 @@ public final class MappingParameters {
 	static final String FIELD_PARAM_SIMILARITY = "similarity";
 	static final String FIELD_PARAM_TERM_VECTOR = "term_vector";
 	static final String FIELD_PARAM_TYPE = "type";
+	static final String FIELD_PARAM_PATH = "path";
+	static final String FIELD_PARAM_TYPE_ALIAS = "alias";
 
 	private final String analyzer;
 	private final boolean coerce;

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

@@ -18,10 +18,7 @@ package org.springframework.data.elasticsearch.core.index;
 
 import static org.assertj.core.api.Assertions.*;
 import static org.springframework.data.elasticsearch.annotations.FieldType.*;
-import static org.springframework.data.elasticsearch.annotations.FieldType.Object;
 
-import java.lang.Integer;
-import java.lang.Object;
 import java.time.Instant;
 import java.time.LocalDate;
 import java.util.Collection;
@@ -269,6 +266,12 @@ public abstract class MappingBuilderIntegrationTests extends MappingContextBaseT
 		operations.indexOps(SimilarityEntity.class).createWithMapping();
 	}
 
+	@Test // #2845
+	@DisplayName("should write mapping with field aliases")
+	void shouldWriteMappingWithFieldAliases() {
+		operations.indexOps(FieldAliasEntity.class).createWithMapping();
+	}
+
 	// region Entities
 	@Document(indexName = "#{@indexNameProvider.indexName()}")
 	static class Book {
@@ -908,5 +911,19 @@ public abstract class MappingBuilderIntegrationTests extends MappingContextBaseT
 		@Field(type = FieldType.Dense_Vector, dims = 42, similarity = "cosine") private double[] denseVector;
 	}
 
+	@Mapping(aliases = {
+			@MappingAlias(name = "someAlly", path = "someText"),
+			@MappingAlias(name = "otherAlly", path = "otherText")
+	})
+	@Document(indexName = "#{@indexNameProvider.indexName()}")
+	private static class FieldAliasEntity {
+		@Id
+		@Nullable private String id;
+		@Nullable
+		@Field(type = Text) private String someText;
+		@Nullable
+		@Field(type = Text) private String otherText;
+	}
+
 	// endregion
 }

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

@@ -19,12 +19,7 @@ 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 static org.springframework.data.elasticsearch.annotations.FieldType.Object;
 
-import java.lang.Boolean;
-import java.lang.Double;
-import java.lang.Integer;
-import java.lang.Object;
 import java.math.BigDecimal;
 import java.time.Instant;
 import java.time.LocalDate;
@@ -1179,6 +1174,39 @@ public class MappingBuilderUnitTests extends MappingContextBaseTests {
 		assertEquals(expected, mapping, true);
 	}
 
+	@Test // #2845
+	@DisplayName("should write field aliases to the mapping")
+	void shouldWriteFieldAliasesToTheMapping() throws JSONException {
+
+		var expected = """
+					{
+					  "properties": {
+					    "_class": {
+					      "type": "keyword",
+					      "index": false,
+					      "doc_values": false
+					    },
+					    "someText": {
+					      "type": "text"
+					    },
+					    "otherText": {
+					      "type": "text"
+					    },
+					    "someAlly": {
+					      "type": "alias",
+					      "path": "someText"
+					    },
+					    "otherAlly": {
+					      "type": "alias",
+					      "path": "otherText"
+					    }
+					  }
+					}
+				""";
+		String mapping = getMappingBuilder().buildPropertyMapping(FieldAliasEntity.class);
+
+		assertEquals(expected, mapping, true);
+	}
 	// region entities
 
 	@Document(indexName = "ignore-above-index")
@@ -1298,8 +1326,8 @@ public class MappingBuilderUnitTests extends MappingContextBaseTests {
 
 			@Nullable
 			@MultiField(mainField = @Field(name = "alternate-description", type = FieldType.Text, analyzer = "whitespace"),
-							otherFields = {
-											@InnerField(suffix = "suff-ix", type = FieldType.Text, analyzer = "stop", searchAnalyzer = "standard") }) //
+					otherFields = {
+							@InnerField(suffix = "suff-ix", type = FieldType.Text, analyzer = "stop", searchAnalyzer = "standard") }) //
 			public String getAlternateDescription() {
 				return alternateDescription;
 			}
@@ -1662,7 +1690,7 @@ public class MappingBuilderUnitTests extends MappingContextBaseTests {
 		@GeoPointField private String pointC;
 		@Nullable
 		@GeoPointField private double[] pointD;
-		// geo shape, until e have the classes for this, us a strng
+
 		@Nullable
 		@GeoShapeField private String shape1;
 		@Nullable
@@ -2390,5 +2418,18 @@ public class MappingBuilderUnitTests extends MappingContextBaseTests {
 		@Nullable
 		@Field(name = "dotted.field", type = Text) private String dottedField;
 	}
+
+	@Mapping(aliases = {
+			@MappingAlias(name = "someAlly", path = "someText"),
+			@MappingAlias(name = "otherAlly", path = "otherText")
+	})
+	private static class FieldAliasEntity {
+		@Id
+		@Nullable private String id;
+		@Nullable
+		@Field(type = Text) private String someText;
+		@Nullable
+		@Field(type = Text) private String otherText;
+	}
 	// endregion
 }