#220 - Introduce R2dbcEntityTemplate.

We now provide a Template API that exposes entity-centric methods. It complements DatabaseClient's simple object mapper methods.

Original pull request: #287.

src/main/java/org/springframework/data/r2dbc/core/DefaultDatabaseClient.java

@@ -204,6 +204,15 @@ protected Mono<Connection> getConnection() {
 		return ConnectionFactoryUtils.getConnection(obtainConnectionFactory());
 	}
 
+	/**
+	 * Obtain the {@link ReactiveDataAccessStrategy}.
+	 *
+	 * @return a the ReactiveDataAccessStrategy.
+	 */
+	protected ReactiveDataAccessStrategy getDataAccessStrategy() {
+		return dataAccessStrategy;
+	}
+
 	/**
 	 * Release the {@link Connection}.
 	 *

src/main/java/org/springframework/data/r2dbc/core/R2dbcEntityOperations.java

@@ -0,0 +1,144 @@
+/*
+ * Copyright 2020 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.r2dbc.core;
+
+import reactor.core.publisher.Flux;
+import reactor.core.publisher.Mono;
+
+import org.springframework.dao.DataAccessException;
+import org.springframework.dao.TransientDataAccessResourceException;
+import org.springframework.data.r2dbc.query.Query;
+import org.springframework.data.r2dbc.query.Update;
+
+/**
+ * Interface specifying a basic set of reactive R2DBC operations using entities. Implemented by
+ * {@link R2dbcEntityTemplate}. Not often used directly, but a useful option to enhance testability, as it can easily be
+ * mocked or stubbed.
+ *
+ * @author Mark Paluch
+ * @since 1.1
+ * @see DatabaseClient
+ */
+public interface R2dbcEntityOperations extends FluentR2dbcOperations {
+
+	/**
+	 * Expose the underlying {@link DatabaseClient} to allow SQL operations.
+	 *
+	 * @return the underlying {@link DatabaseClient}.
+	 * @see DatabaseClient
+	 */
+	DatabaseClient getDatabaseClient();
+
+	// -------------------------------------------------------------------------
+	// Methods dealing with org.springframework.data.r2dbc.query.Query
+	// -------------------------------------------------------------------------
+
+	/**
+	 * Returns the number of rows for the given entity class applying {@link Query}. This overridden method allows users
+	 * to further refine the selection Query using a {@link Query} predicate to determine how many entities of the given
+	 * {@link Class type} match the Query.
+	 *
+	 * @param query user-defined count {@link Query} to execute; must not be {@literal null}.
+	 * @param entityClass {@link Class type} of the entity; must not be {@literal null}.
+	 * @return the number of existing entities.
+	 * @throws DataAccessException if any problem occurs while executing the query.
+	 */
+	Mono<Long> count(Query query, Class<?> entityClass) throws DataAccessException;
+
+	/**
+	 * Determine whether the result for {@code entityClass} {@link Query} yields at least one row.
+	 *
+	 * @param query user-defined exists {@link Query} to execute; must not be {@literal null}.
+	 * @param entityClass {@link Class type} of the entity; must not be {@literal null}.
+	 * @return {@literal true} if the object exists.
+	 * @throws DataAccessException if any problem occurs while executing the query.
+	 * @since 2.1
+	 */
+	Mono<Boolean> exists(Query query, Class<?> entityClass) throws DataAccessException;
+
+	/**
+	 * Execute a {@code SELECT} query and convert the resulting items to a stream of entities.
+	 *
+	 * @param query must not be {@literal null}.
+	 * @param entityClass The entity type must not be {@literal null}.
+	 * @return the result objects returned by the action.
+	 * @throws DataAccessException if there is any problem issuing the execution.
+	 */
+	<T> Flux<T> select(Query query, Class<T> entityClass) throws DataAccessException;
+
+	/**
+	 * Execute a {@code SELECT} query and convert the resulting item to an entity.
+	 *
+	 * @param query must not be {@literal null}.
+	 * @param entityClass The entity type must not be {@literal null}.
+	 * @return the result object returned by the action or {@link Mono#empty()}.
+	 * @throws DataAccessException if there is any problem issuing the execution.
+	 */
+	<T> Mono<T> selectOne(Query query, Class<T> entityClass) throws DataAccessException;
+
+	/**
+	 * Update the queried entities and return {@literal true} if the update was applied.
+	 *
+	 * @param query must not be {@literal null}.
+	 * @param update must not be {@literal null}.
+	 * @param entityClass The entity type must not be {@literal null}.
+	 * @return the number of affected rows.
+	 * @throws DataAccessException if there is any problem executing the query.
+	 */
+	Mono<Integer> update(Query query, Update update, Class<?> entityClass) throws DataAccessException;
+
+	/**
+	 * Remove entities (rows)/columns from the table by {@link Query}.
+	 *
+	 * @param query must not be {@literal null}.
+	 * @param entityClass The entity type must not be {@literal null}.
+	 * @return the number of affected rows.
+	 * @throws DataAccessException if there is any problem issuing the execution.
+	 */
+	Mono<Integer> delete(Query query, Class<?> entityClass) throws DataAccessException;
+
+	// -------------------------------------------------------------------------
+	// Methods dealing with entities
+	// -------------------------------------------------------------------------
+
+	/**
+	 * Insert the given entity and emit the entity if the insert was applied.
+	 *
+	 * @param entity The entity to insert, must not be {@literal null}.
+	 * @return the inserted entity.
+	 * @throws DataAccessException if there is any problem issuing the execution.
+	 */
+	<T> Mono<T> insert(T entity) throws DataAccessException;
+
+	/**
+	 * Update the given entity and emit the entity if the update was applied.
+	 *
+	 * @param entity The entity to update, must not be {@literal null}.
+	 * @return the updated entity.
+	 * @throws DataAccessException if there is any problem issuing the execution.
+	 * @throws TransientDataAccessResourceException if the update did not affect any rows.
+	 */
+	<T> Mono<T> update(T entity) throws DataAccessException;
+
+	/**
+	 * Delete the given entity and emit the entity if the delete was applied.
+	 *
+	 * @param entity must not be {@literal null}.
+	 * @return the deleted entity.
+	 * @throws DataAccessException if there is any problem issuing the execution.
+	 */
+	<T> Mono<T> delete(T entity) throws DataAccessException;
+}