Polishing.

Use FilterFunction instead of nullable fetchSize to avoid unconditional capturing lambdas and improve defaulting.

Add since tag.

See #1652
Original pull request: #1898

spring-data-r2dbc/src/main/java/org/springframework/data/r2dbc/core/R2dbcEntityTemplate.java

@@ -18,6 +18,7 @@ package org.springframework.data.r2dbc.core;
 import io.r2dbc.spi.ConnectionFactory;
 import io.r2dbc.spi.Row;
 import io.r2dbc.spi.RowMetadata;
+import io.r2dbc.spi.Statement;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -320,7 +321,8 @@ public class R2dbcEntityTemplate implements R2dbcEntityOperations, BeanFactoryAw
 	<T, P extends Publisher<T>> P doSelect(Query query, Class<?> entityClass, SqlIdentifier tableName,
 			Class<T> returnType, Function<RowsFetchSpec<T>, P> resultHandler, @Nullable Integer fetchSize) {
 
-		RowsFetchSpec<T> fetchSpec = doSelect(query, entityClass, tableName, returnType, fetchSize);
+		RowsFetchSpec<T> fetchSpec = doSelect(query, entityClass, tableName, returnType,
+				fetchSize != null ? statement -> statement.fetchSize(fetchSize) : Function.identity());
 
 		P result = resultHandler.apply(fetchSpec);
 
@@ -332,7 +334,7 @@ public class R2dbcEntityTemplate implements R2dbcEntityOperations, BeanFactoryAw
 	}
 
 	private <T> RowsFetchSpec<T> doSelect(Query query, Class<?> entityType, SqlIdentifier tableName,
-			Class<T> returnType, @Nullable Integer fetchSize) {
+			Class<T> returnType, Function<? super Statement, ? extends Statement> filterFunction) {
 
 		StatementMapper statementMapper = dataAccessStrategy.getStatementMapper().forType(entityType);
 
@@ -360,7 +362,7 @@ public class R2dbcEntityTemplate implements R2dbcEntityOperations, BeanFactoryAw
 		PreparedOperation<?> operation = statementMapper.getMappedObject(selectSpec);
 
 		return getRowsFetchSpec(
-			databaseClient.sql(operation).filter((statement) -> statement.fetchSize(Optional.ofNullable(fetchSize).orElse(0))),
+				databaseClient.sql(operation).filter(filterFunction),
 			entityType,
 			returnType
 		);

spring-data-r2dbc/src/main/java/org/springframework/data/r2dbc/core/ReactiveSelectOperation.java

@@ -118,10 +118,12 @@ public interface ReactiveSelectOperation {
 	interface SelectWithQuery<T> extends TerminatingSelect<T> {
 
 		/**
-		 * Specifies the fetch size for this query
+		 * Specifies the fetch size for this query.
 		 *
 		 * @param fetchSize
-		 * @return
+		 * @return new instance of {@link SelectWithQuery}.
+		 * @since 3.4
+		 * @see io.r2dbc.spi.Statement#fetchSize(int)
 		 */
 		SelectWithQuery<T> withFetchSize(int fetchSize);
 

spring-data-r2dbc/src/main/java/org/springframework/data/r2dbc/core/ReactiveSelectOperationSupport.java

@@ -54,7 +54,6 @@ class ReactiveSelectOperationSupport implements ReactiveSelectOperation {
 		private final Class<T> returnType;
 		private final Query query;
 		private final @Nullable SqlIdentifier tableName;
-
 		private final @Nullable Integer fetchSize;
 
 		ReactiveSelectSupport(R2dbcEntityTemplate template, Class<?> domainType, Class<T> returnType, Query query,
@@ -86,9 +85,6 @@ class ReactiveSelectOperationSupport implements ReactiveSelectOperation {
 
 		@Override
 		public SelectWithQuery<T> withFetchSize(int fetchSize) {
-
-			Assert.notNull(returnType, "FetchSize must not be null");
-
 			return new ReactiveSelectSupport<>(template, domainType, returnType, query, tableName, fetchSize);
 		}