#109 - Fix simple type conversion for projection queries.

 We now correctly consider built-in converters for simple types that are read through DatabaseClient. Simple type projections typically select a single column and expect a result stream of simple values such as selecting a count and retrieving a Mono<Long>.

Author: mp911de

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

@@ -76,7 +76,8 @@ private static R2dbcConverter createConverter(Dialect dialect) {
 		Assert.notNull(dialect, "Dialect must not be null");
 
 		R2dbcCustomConversions customConversions = new R2dbcCustomConversions(
-				StoreConversions.of(dialect.getSimpleTypeHolder()), Collections.emptyList());
+				StoreConversions.of(dialect.getSimpleTypeHolder(), R2dbcCustomConversions.STORE_CONVERTERS),
+				Collections.emptyList());
 
 		RelationalMappingContext context = new RelationalMappingContext();
 		context.setSimpleTypeHolder(customConversions.getSimpleTypeHolder());

src/test/java/org/springframework/data/r2dbc/config/H2IntegrationTests.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright 2019 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.config;
+
+import io.r2dbc.spi.ConnectionFactory;
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.FilterType;
+import org.springframework.dao.DataAccessException;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.r2dbc.core.DatabaseClient;
+import org.springframework.data.r2dbc.repository.config.EnableR2dbcRepositories;
+import org.springframework.data.r2dbc.repository.query.Query;
+import org.springframework.data.r2dbc.testing.H2TestSupport;
+import org.springframework.data.relational.core.mapping.Table;
+import org.springframework.data.repository.reactive.ReactiveCrudRepository;
+import org.springframework.jdbc.core.JdbcTemplate;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringRunner;
+
+/**
+ * Integration test for {@link DatabaseClient} and repositories using H2.
+ *
+ * @author Mark Paluch
+ */
+@RunWith(SpringRunner.class)
+@ContextConfiguration
+public class H2IntegrationTests {
+
+	private JdbcTemplate jdbc = new JdbcTemplate(H2TestSupport.createDataSource());
+
+	@Autowired DatabaseClient databaseClient;
+	@Autowired H2Repository repository;
+
+	@Before
+	public void before() {
+
+		try {
+			jdbc.execute("DROP TABLE legoset");
+		} catch (DataAccessException e) {}
+		jdbc.execute(H2TestSupport.CREATE_TABLE_LEGOSET);
+	}
+
+	@Test // gh-109
+	public void shouldSelectCountWithDatabaseClient() {
+
+		jdbc.execute("INSERT INTO legoset (id, name, manual) VALUES(42055, 'SCHAUFELRADBAGGER', 12)");
+
+		databaseClient.execute().sql("SELECT COUNT(*) FROM legoset") //
+				.as(Long.class) //
+				.fetch() //
+				.all() //
+				.as(StepVerifier::create) //
+				.expectNext(1L) //
+				.verifyComplete();
+	}
+
+	@Test // gh-109
+	public void shouldSelectCountWithRepository() {
+
+		jdbc.execute("INSERT INTO legoset (id, name, manual) VALUES(42055, 'SCHAUFELRADBAGGER', 12)");
+
+		repository.selectCount() //
+				.as(StepVerifier::create) //
+				.expectNext(1L) //
+				.verifyComplete();
+	}
+
+	@Configuration
+	@EnableR2dbcRepositories(considerNestedRepositories = true,
+			includeFilters = @ComponentScan.Filter(type = FilterType.ASSIGNABLE_TYPE, classes = H2Repository.class),
+			basePackageClasses = H2Repository.class)
+	static class H2Configuration extends AbstractR2dbcConfiguration {
+
+		@Override
+		public ConnectionFactory connectionFactory() {
+			return H2TestSupport.createConnectionFactory();
+		}
+	}
+
+	interface H2Repository extends ReactiveCrudRepository<LegoSet, Integer> {
+
+		@Query("SELECT COUNT(*) FROM legoset")
+		Mono<Long> selectCount();
+	}
+
+	@Data
+	@Table("legoset")
+	@AllArgsConstructor
+	@NoArgsConstructor
+	static class LegoSet {
+		@Id Integer id;
+		String name;
+		Integer manual;
+	}
+}

src/test/java/org/springframework/data/r2dbc/core/AbstractDatabaseClientIntegrationTests.java

@@ -33,7 +33,6 @@
 import org.springframework.data.annotation.Id;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Sort;
-import org.springframework.data.r2dbc.core.DatabaseClient;
 import org.springframework.data.r2dbc.query.Criteria;
 import org.springframework.data.r2dbc.query.Update;
 import org.springframework.data.r2dbc.testing.R2dbcIntegrationTestSupport;
@@ -340,6 +339,30 @@ public void selectExtracting() {
 				.verifyComplete();
 	}
 
+	@Test // gh-109
+	public void selectSimpleTypeProjection() {
+
+		jdbc.execute("INSERT INTO legoset (id, name, manual) VALUES(42055, 'SCHAUFELRADBAGGER', 12)");
+
+		DatabaseClient databaseClient = DatabaseClient.create(connectionFactory);
+
+		databaseClient.execute().sql("SELECT COUNT(*) FROM legoset") //
+				.as(Long.class) //
+				.fetch() //
+				.all() //
+				.as(StepVerifier::create) //
+				.expectNext(1L) //
+				.verifyComplete();
+
+		databaseClient.execute().sql("SELECT name FROM legoset") //
+				.as(String.class) //
+				.fetch() //
+				.one() //
+				.as(StepVerifier::create) //
+				.expectNext("SCHAUFELRADBAGGER") //
+				.verifyComplete();
+	}
+
 	@Test // gh-8
 	public void selectWithCriteria() {