Allow explicit index mapping writing on repository startup.

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

@@ -58,6 +58,13 @@
 	 */
 	boolean createIndex() default true;
 
+	/**
+	 * If true, the index mapping will be written on repository bootstrapping even when the index already exists. This
+	 * allows for automatically updating the mapping with new properties. Changes on existing properties will lead to an
+	 * error from the Elasticsearch server.
+	 */
+	boolean alwaysWriteMapping() default false;
+
 	/**
 	 * Configuration of version management.
 	 */

src/main/java/org/springframework/data/elasticsearch/core/mapping/ElasticsearchPersistentEntity.java

@@ -187,4 +187,10 @@ default ElasticsearchPersistentProperty getRequiredSeqNoPrimaryTermProperty() {
 	 * @since 5.1
 	 */
 	boolean storeVersionInSource();
+
+	/**
+	 * @return if the mapping should be written to the index on repositry bootstrap even if the index already exists.
+	 * @since 5.2
+	 */
+	boolean isAlwaysWriteMapping();
 }

src/main/java/org/springframework/data/elasticsearch/core/mapping/SimpleElasticsearchPersistentEntity.java

@@ -74,6 +74,7 @@ public class SimpleElasticsearchPersistentEntity<T> extends BasicPersistentEntit
 	private @Nullable ElasticsearchPersistentProperty indexedIndexNameProperty;
 	private @Nullable Document.VersionType versionType;
 	private boolean createIndexAndMapping;
+	private boolean alwaysWriteMapping;
 	private final Dynamic dynamic;
 	private final Map<String, ElasticsearchPersistentProperty> fieldNamePropertyCache = new ConcurrentHashMap<>();
 	private final ConcurrentHashMap<String, Expression> routingExpressions = new ConcurrentHashMap<>();
@@ -107,13 +108,16 @@ public SimpleElasticsearchPersistentEntity(TypeInformation<T> typeInformation,
 			this.indexName = document.indexName();
 			this.versionType = document.versionType();
 			this.createIndexAndMapping = document.createIndex();
+			this.alwaysWriteMapping = document.alwaysWriteMapping();
 			this.dynamic = document.dynamic();
 			this.storeIdInSource = document.storeIdInSource();
 			this.storeVersionInSource = document.storeVersionInSource();
 		} else {
 			this.dynamic = Dynamic.INHERIT;
 			this.storeIdInSource = true;
 			this.storeVersionInSource = true;
+			this.createIndexAndMapping = false;
+			this.alwaysWriteMapping = false;
 		}
 		Routing routingAnnotation = AnnotatedElementUtils.findMergedAnnotation(clazz, Routing.class);
 
@@ -172,6 +176,10 @@ public boolean isCreateIndexAndMapping() {
 		return createIndexAndMapping;
 	}
 
+	public boolean isAlwaysWriteMapping() {
+		return alwaysWriteMapping;
+	}
+
 	@Override
 	public FieldNamingStrategy getFieldNamingStrategy() {
 		return contextConfiguration.getFieldNamingStrategy();

src/main/java/org/springframework/data/elasticsearch/repository/support/SimpleElasticsearchRepository.java

@@ -82,6 +82,8 @@ public SimpleElasticsearchRepository(ElasticsearchEntityInformation<T, ID> metad
 
 		if (shouldCreateIndexAndMapping() && !indexOperations.exists()) {
 			indexOperations.createWithMapping();
+		} else if (shouldAlwaysWriteMapping()) {
+			indexOperations.putMapping();
 		}
 	}
 
@@ -92,6 +94,11 @@ private boolean shouldCreateIndexAndMapping() {
 		return entity.isCreateIndexAndMapping();
 	}
 
+	private boolean shouldAlwaysWriteMapping() {
+		return operations.getElasticsearchConverter().getMappingContext()
+				.getRequiredPersistentEntity(entityClass).isAlwaysWriteMapping();
+	}
+
 	@Override
 	public Optional<T> findById(ID id) {
 		return Optional.ofNullable(

src/main/java/org/springframework/data/elasticsearch/repository/support/SimpleReactiveElasticsearchRepository.java

@@ -66,6 +66,8 @@ private void createIndexAndMappingIfNeeded() {
 			indexOperations.exists() //
 					.flatMap(exists -> exists ? Mono.empty() : indexOperations.createWithMapping()) //
 					.block();
+		} else if(shouldAlwaysWriteMapping()) {
+			indexOperations.putMapping().block();
 		}
 	}
 
@@ -76,6 +78,11 @@ private boolean shouldCreateIndexAndMapping() {
 		return entity.isCreateIndexAndMapping();
 	}
 
+	private boolean shouldAlwaysWriteMapping() {
+		return operations.getElasticsearchConverter().getMappingContext()
+				.getRequiredPersistentEntity(entityInformation.getJavaType()).isAlwaysWriteMapping();
+	}
+
 	@Override
 	public <S extends T> Mono<S> save(S entity) {