#468 - Correctly map result of exists queries.

We now map results of exists queries to a boolean flag to ensure proper decoding. Previously, results were attempted to be mapped onto a primitive type which failed as there's no converter registered for Row to Boolean.

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

@@ -89,17 +89,21 @@ public abstract class AbstractR2dbcQuery implements RepositoryQuery {
 		return createQuery(parameterAccessor).flatMapMany(it -> executeQuery(parameterAccessor, it));
 	}
 
+	@SuppressWarnings({ "unchecked", "rawtypes" })
 	private Publisher<?> executeQuery(RelationalParameterAccessor parameterAccessor, BindableQuery it) {
 
 		ResultProcessor processor = method.getResultProcessor().withDynamicProjection(parameterAccessor);
 		DatabaseClient.GenericExecuteSpec boundQuery = it.bind(databaseClient.sql(it));
 
-		FetchSpec<?> fetchSpec;
-		if (requiresMapping()) {
-			EntityRowMapper<?> rowMapper = new EntityRowMapper<>(resolveResultType(processor), converter);
+		FetchSpec<Object> fetchSpec;
+
+		if (isExistsQuery()) {
+			fetchSpec = (FetchSpec) boundQuery.map(row -> true);
+		} else if (requiresMapping()) {
+			EntityRowMapper rowMapper = new EntityRowMapper<>(resolveResultType(processor), converter);
 			fetchSpec = new FetchSpecAdapter<>(boundQuery.map(rowMapper));
 		} else {
-			fetchSpec = boundQuery.fetch();
+			fetchSpec = (FetchSpec) boundQuery.fetch();
 		}
 
 		SqlIdentifier tableName = method.getEntityInformation().getTableName();
@@ -143,6 +147,14 @@ public abstract class AbstractR2dbcQuery implements RepositoryQuery {
 			return (q, t, c) -> q.rowsUpdated();
 		}
 
+		if (isCountQuery()) {
+			return (q, t, c) -> q.first().defaultIfEmpty(0L);
+		}
+
+		if (isExistsQuery()) {
+			return (q, t, c) -> q.first().defaultIfEmpty(false);
+		}
+
 		if (method.isCollectionQuery()) {
 			return (q, t, c) -> q.all();
 		}
@@ -158,6 +170,22 @@ public abstract class AbstractR2dbcQuery implements RepositoryQuery {
 	 */
 	protected abstract boolean isModifyingQuery();
 
+	/**
+	 * Returns whether the query should get a count projection applied.
+	 *
+	 * @return
+	 * @since 1.2
+	 */
+	protected abstract boolean isCountQuery();
+
+	/**
+	 * Returns whether the query should get an exists projection applied.
+	 *
+	 * @return
+	 * @since 1.2
+	 */
+	protected abstract boolean isExistsQuery();
+
 	/**
 	 * Creates a {@link BindableQuery} instance using the given {@link ParameterAccessor}
 	 *

src/main/java/org/springframework/data/r2dbc/repository/query/PartTreeR2dbcQuery.java

@@ -82,6 +82,24 @@ public class PartTreeR2dbcQuery extends AbstractR2dbcQuery {
 		return this.tree.isDelete();
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.r2dbc.repository.query.AbstractR2dbcQuery#isCountQuery()
+	 */
+	@Override
+	protected boolean isCountQuery() {
+		return this.tree.isCountProjection();
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.r2dbc.repository.query.AbstractR2dbcQuery#isExistsQuery()
+	 */
+	@Override
+	protected boolean isExistsQuery() {
+		return this.tree.isExistsProjection();
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.r2dbc.repository.query.AbstractR2dbcQuery#createQuery(org.springframework.data.relational.repository.query.RelationalParameterAccessor)

src/main/java/org/springframework/data/r2dbc/repository/query/R2dbcQueryExecution.java

@@ -41,7 +41,7 @@ import org.springframework.util.ClassUtils;
  */
 interface R2dbcQueryExecution {
 
-	Publisher<?> execute(FetchSpec<?> query, Class<?> type, SqlIdentifier tableName);
+	Publisher<?> execute(FetchSpec<Object> query, Class<?> type, SqlIdentifier tableName);
 
 	/**
 	 * An {@link R2dbcQueryExecution} that wraps the results of the given delegate with the given result processing.
@@ -60,8 +60,8 @@ interface R2dbcQueryExecution {
 		 * @see org.springframework.data.r2dbc.repository.query.R2dbcQueryExecution#execute(org.springframework.data.r2dbc.function.FetchSpec, java.lang.Class, java.lang.String)
 		 */
 		@Override
-		public Publisher<?> execute(FetchSpec<?> query, Class<?> type, SqlIdentifier tableName) {
-			return (Publisher<?>) this.converter.convert(this.delegate.execute(query, type, tableName));
+		public Publisher<Object> execute(FetchSpec<Object> query, Class<?> type, SqlIdentifier tableName) {
+			return (Publisher<Object>) this.converter.convert(this.delegate.execute(query, type, tableName));
 		}
 	}
 

src/main/java/org/springframework/data/r2dbc/repository/query/StringBasedR2dbcQuery.java

@@ -112,6 +112,24 @@ public class StringBasedR2dbcQuery extends AbstractR2dbcQuery {
 		return getQueryMethod().isModifyingQuery();
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.r2dbc.repository.query.AbstractR2dbcQuery#isCountQuery()
+	 */
+	@Override
+	protected boolean isCountQuery() {
+		return false;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.r2dbc.repository.query.AbstractR2dbcQuery#isExistsQuery()
+	 */
+	@Override
+	protected boolean isExistsQuery() {
+		return false;
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.r2dbc.repository.query.AbstractR2dbcQuery#createQuery(org.springframework.data.relational.repository.query.RelationalParameterAccessor)
@@ -133,6 +151,7 @@ public class StringBasedR2dbcQuery extends AbstractR2dbcQuery {
 		});
 	}
 
+
 	private Mono<R2dbcSpELExpressionEvaluator> getSpelEvaluator(RelationalParameterAccessor accessor) {
 
 		return evaluationContextProvider

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

@@ -296,6 +296,33 @@ public abstract class AbstractR2dbcRepositoryIntegrationTests extends R2dbcInteg
 				.verifyComplete();
 	}
 
+	@Test // gh-363
+	void derivedQueryWithCount() {
+
+		shouldInsertNewItems();
+
+		repository.countByNameContains("SCH") //
+				.as(StepVerifier::create) //
+				.assertNext(i -> assertThat(i).isEqualTo(2)) //
+				.verifyComplete();
+	}
+
+	@Test // gh-468
+	void derivedQueryWithExists() {
+
+		shouldInsertNewItems();
+
+		repository.existsByName("ABS") //
+				.as(StepVerifier::create) //
+				.expectNext(Boolean.FALSE) //
+				.verifyComplete();
+
+		repository.existsByName("SCHAUFELRADBAGGER") //
+				.as(StepVerifier::create) //
+				.expectNext(true) //
+				.verifyComplete();
+	}
+
 	@Test // gh-421
 	void shouldDeleteAllAndReturnCount() {
 
@@ -345,6 +372,8 @@ public abstract class AbstractR2dbcRepositoryIntegrationTests extends R2dbcInteg
 		Mono<Integer> deleteAllAndReturnCount();
 
 		Mono<Integer> countByNameContains(String namePart);
+
+		Mono<Boolean> existsByName(String name);
 	}
 
 	@Getter