#421 - Handle modifying query methods returning kotlin.Unit.

Added check for kotlin.Unit to AbstractR2dbcQuery#getExecutionToWrap. This case is essentially equivalent to a return type of Void, but the singleton Unit instance needs to be returned instead of discarding the result entirely.

It was also necessary to add a check to R2dbcQueryMethod#getEntityInformation, as otherwise a PersistentEntity is created for Unit, which leads to a new instance being created via reflection down the pipeline (which is probably not a thing that should happen).

Original pull request: #422.

Author: ada-waffles

src/main/asciidoc/reference/r2dbc-repositories.adoc

@@ -267,7 +267,7 @@ Mono<Integer> setFixedFirstnameFor(String firstname, String lastname);
 
 The result of a modifying query can be:
 
-* `Void` to discard update count and await completion.
+* `Void` (or Kotlin `Unit`) to discard update count and await completion.
 * `Integer` or another numeric type emitting the affected rows count.
 * `Boolean` to emit whether at least one row was updated.
 

src/main/java/org/springframework/data/r2dbc/repository/query/AbstractR2dbcQuery.java

@@ -15,11 +15,13 @@
  */
 package org.springframework.data.r2dbc.repository.query;
 
+import kotlin.Unit;
+
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.reactivestreams.Publisher;
-
+import org.springframework.core.KotlinDetector;
 import org.springframework.data.mapping.model.EntityInstantiators;
 import org.springframework.data.r2dbc.convert.R2dbcConverter;
 import org.springframework.data.r2dbc.core.DatabaseClient;
@@ -41,6 +43,7 @@
  * Base class for reactive {@link RepositoryQuery} implementations for R2DBC.
  *
  * @author Mark Paluch
+ * @author Stephen Cohen
  */
 public abstract class AbstractR2dbcQuery implements RepositoryQuery {
 
@@ -141,6 +144,10 @@ private R2dbcQueryExecution getExecutionToWrap(ReturnedType returnedType) {
 				return (q, t, c) -> q.rowsUpdated().then();
 			}
 
+			if (KotlinDetector.isKotlinPresent() && Unit.class.isAssignableFrom(returnedType.getReturnedType())) {
+				return (q, t, c) -> q.rowsUpdated().thenReturn(Unit.INSTANCE);
+			}
+
 			return (q, t, c) -> q.rowsUpdated();
 		}
 

src/main/java/org/springframework/data/r2dbc/repository/query/R2dbcQueryMethod.java

@@ -17,9 +17,12 @@
 
 import static org.springframework.data.repository.util.ClassUtils.*;
 
+import kotlin.Unit;
+
 import java.lang.reflect.Method;
 import java.util.Optional;
 
+import org.springframework.core.KotlinDetector;
 import org.springframework.core.annotation.AnnotatedElementUtils;
 import org.springframework.dao.InvalidDataAccessApiUsageException;
 import org.springframework.data.domain.Page;
@@ -51,6 +54,7 @@
  * Reactive specific implementation of {@link QueryMethod}.
  *
  * @author Mark Paluch
+ * @author Stephen Cohen
  */
 public class R2dbcQueryMethod extends QueryMethod {
 
@@ -164,7 +168,8 @@ public RelationalEntityMetadata<?> getEntityInformation() {
 			Class<?> returnedObjectType = getReturnedObjectType();
 			Class<?> domainClass = getDomainClass();
 
-			if (ClassUtils.isPrimitiveOrWrapper(returnedObjectType)) {
+			if (ClassUtils.isPrimitiveOrWrapper(returnedObjectType)
+					|| KotlinDetector.isKotlinPresent() && Unit.class.isAssignableFrom(returnedObjectType)) {
 
 				this.metadata = new SimpleRelationalEntityMetadata<>((Class<Object>) domainClass,
 						mappingContext.getRequiredPersistentEntity(domainClass));

src/test/java/org/springframework/data/r2dbc/repository/AbstractR2dbcRepositoryIntegrationTests.java

@@ -17,6 +17,8 @@
 
 import static org.assertj.core.api.Assertions.*;
 
+import kotlin.Unit;
+
 import io.r2dbc.spi.ConnectionFactory;
 import lombok.AllArgsConstructor;
 import lombok.Getter;
@@ -297,6 +299,55 @@ public void derivedQueryWithCountProjection() {
 				.verifyComplete();
 	}
 
+	@Test // gh-421
+	public void shouldDeleteAllAndReturnCount() {
+
+		shouldInsertNewItems();
+
+		repository.deleteAllAndReturnCount() //
+				.as(StepVerifier::create) //
+				.expectNext(2) //
+				.verifyComplete();
+
+		repository.findAll() //
+				.as(StepVerifier::create) //
+				.verifyComplete();
+	}
+
+	@Test // gh-421
+	public void shouldDeleteAndReturnSuccess() {
+
+		shouldInsertNewItems();
+
+		repository.deleteByManualAndReturnSuccess(12) //
+				.as(StepVerifier::create) //
+				.expectNext(true) //
+				.verifyComplete();
+
+		repository.findAll() //
+				.map(LegoSet::getManual) //
+				.as(StepVerifier::create) //
+				.expectNext(13) //
+				.verifyComplete();
+	}
+
+	@Test // gh-421
+	public void shouldDeleteAndReturnKotlinUnit() {
+
+		shouldInsertNewItems();
+
+		repository.deleteByManualAndReturnKotlinUnit(12) //
+				.as(StepVerifier::create) //
+				.expectNext(Unit.INSTANCE) //
+				.verifyComplete();
+
+		repository.findAll() //
+				.map(LegoSet::getManual) //
+				.as(StepVerifier::create) //
+				.expectNext(13) //
+				.verifyComplete();
+	}
+
 	private Condition<? super Object> numberOf(int expected) {
 		return new Condition<>(it -> {
 			return it instanceof Number && ((Number) it).intValue() == expected;
@@ -322,9 +373,22 @@ interface LegoSetRepository extends ReactiveSortingRepository<LegoSet, Integer>
 
 		Mono<Void> deleteAllBy();
 
+		@Modifying
 		@Query("DELETE from legoset where manual = :manual")
 		Mono<Void> deleteAllByManual(int manual);
 
+		@Modifying
+		@Query("DELETE from legoset")
+		Mono<Integer> deleteAllAndReturnCount();
+
+		@Modifying
+		@Query("DELETE from legoset where manual = :manual")
+		Mono<Boolean> deleteByManualAndReturnSuccess(int manual);
+
+		@Modifying
+		@Query("DELETE from legoset where manual = :manual")
+		Mono<Unit> deleteByManualAndReturnKotlinUnit(int manual);
+
 		Mono<Integer> countByNameContains(String namePart);
 	}
 

src/test/java/org/springframework/data/r2dbc/repository/query/R2dbcQueryMethodUnitTests.java

@@ -17,6 +17,8 @@
 
 import static org.assertj.core.api.Assertions.*;
 
+import kotlin.Unit;
+
 import reactor.core.publisher.Mono;
 
 import java.lang.annotation.Retention;
@@ -45,6 +47,7 @@
  * Unit test for {@link R2dbcQueryMethod}.
  *
  * @author Mark Paluch
+ * @author Stephen Cohen
  */
 public class R2dbcQueryMethodUnitTests {
 
@@ -128,6 +131,14 @@ public void fallsBackToRepositoryDomainTypeIfMethodDoesNotReturnADomainType() th
 		assertThat(method.getEntityInformation().getJavaType()).isAssignableFrom(Contact.class);
 	}
 
+	@Test // gh-421
+	public void fallsBackToRepositoryDomainTypeIfMethodReturnsKotlinUnit() throws Exception {
+
+		R2dbcQueryMethod method = queryMethod(PersonRepository.class, "deleteByFirstname", String.class);
+
+		assertThat(method.getEntityInformation().getJavaType()).isAssignableFrom(Contact.class);
+	}
+
 	private R2dbcQueryMethod queryMethod(Class<?> repository, String name, Class<?>... parameters) throws Exception {
 
 		Method method = repository.getMethod(name, parameters);
@@ -144,6 +155,8 @@ interface PersonRepository extends Repository<Contact, Long> {
 		Mono<Slice<Contact>> findMonoSliceByLastname(String lastname, Pageable pageRequest);
 
 		void deleteByUserName(String userName);
+
+		Unit deleteByFirstname(String firstname);
 	}
 
 	interface SampleRepository extends Repository<Contact, Long> {