Provide more expressive exception for projections without properties.

Closes #1813

Author: schauder

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/repository/query/JdbcQueryCreator.java

@@ -33,6 +33,7 @@
 import org.springframework.data.relational.core.mapping.RelationalPersistentProperty;
 import org.springframework.data.relational.core.query.Criteria;
 import org.springframework.data.relational.core.sql.Column;
+import org.springframework.data.relational.core.sql.EmptySelectListException;
 import org.springframework.data.relational.core.sql.Expression;
 import org.springframework.data.relational.core.sql.Expressions;
 import org.springframework.data.relational.core.sql.Functions;
@@ -177,13 +178,23 @@ protected ParametrizedQuery complete(@Nullable Criteria criteria, Sort sort) {
 			completedBuildSelect = selectOrderBuilder.lock(this.lockMode.get().value());
 		}
 
-		Select select = completedBuildSelect.build();
+		Select select = getSelect(completedBuildSelect);
 
 		String sql = SqlRenderer.create(renderContextFactory.createRenderContext()).render(select);
 
 		return new ParametrizedQuery(sql, parameterSource);
 	}
 
+	private Select getSelect(SelectBuilder.BuildSelect completedBuildSelect) {
+
+		try {
+			return completedBuildSelect.build();
+		} catch (EmptySelectListException cause) {
+			throw new IllegalStateException(
+					returnedType.getReturnedType().getName() + " does not define any properties to select", cause);
+		}
+	}
+
 	SelectBuilder.SelectOrdered applyOrderBy(Sort sort, RelationalPersistentEntity<?> entity, Table table,
 			SelectBuilder.SelectOrdered selectOrdered) {
 

spring-data-jdbc/src/test/java/org/springframework/data/jdbc/repository/JdbcRepositoryIntegrationTests.java

@@ -41,7 +41,6 @@
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.Arguments;
 import org.junit.jupiter.params.provider.MethodSource;
-
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.config.PropertiesFactoryBean;
 import org.springframework.context.ApplicationListener;
@@ -51,16 +50,7 @@
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.dao.IncorrectResultSizeDataAccessException;
 import org.springframework.data.annotation.Id;
-import org.springframework.data.domain.Example;
-import org.springframework.data.domain.ExampleMatcher;
-import org.springframework.data.domain.Limit;
-import org.springframework.data.domain.Page;
-import org.springframework.data.domain.PageRequest;
-import org.springframework.data.domain.Pageable;
-import org.springframework.data.domain.ScrollPosition;
-import org.springframework.data.domain.Slice;
-import org.springframework.data.domain.Sort;
-import org.springframework.data.domain.Window;
+import org.springframework.data.domain.*;
 import org.springframework.data.jdbc.core.mapping.AggregateReference;
 import org.springframework.data.jdbc.repository.query.Modifying;
 import org.springframework.data.jdbc.repository.query.Query;
@@ -572,6 +562,24 @@ public void partTreeQueryProjectionShouldReturnProjectedEntities() {
 		assertThat(result.get(0).getName()).isEqualTo("Entity Name");
 	}
 
+	@Test // GH-1813
+	public void partTreeQueryDynamicProjectionShouldReturnProjectedEntities() {
+
+		repository.save(createDummyEntity());
+
+		List<DummyProjection> result = repository.findDynamicProjectedByName("Entity Name", DummyProjection.class);
+
+		assertThat(result).hasSize(1);
+		assertThat(result.get(0).getName()).isEqualTo("Entity Name");
+	}
+
+	@Test // GH-1813
+	public void partTreeQueryDynamicProjectionWithBrokenProjectionShouldError() {
+
+		assertThatThrownBy(() -> repository.findDynamicProjectedByName("Entity Name", BrokenProjection.class))
+				.hasMessageContaining("BrokenProjection does not define any properties to select");
+	}
+
 	@Test // GH-971
 	public void pageQueryProjectionShouldReturnProjectedEntities() {
 
@@ -1428,6 +1436,8 @@ interface DummyEntityRepository extends CrudRepository<DummyEntity, Long>, Query
 
 		List<DummyProjection> findProjectedByName(String name);
 
+		<T> List<T> findDynamicProjectedByName(String name, Class<T> projection);
+
 		@Query(value = "SELECT * FROM DUMMY_ENTITY", rowMapperClass = CustomRowMapper.class)
 		List<DummyEntity> findAllWithCustomMapper();
 
@@ -1941,6 +1951,10 @@ interface DummyProjection {
 		String getName();
 	}
 
+	interface BrokenProjection {
+		String name();
+	}
+
 	static final class DtoProjection {
 		private final String name;
 

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/EmptySelectListException.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2024 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.relational.core.sql;
+
+/**
+ * Exception denoting the absence of a select list from a query.
+ *
+ * @author Jens Schauder
+ * @since 3.4
+ */
+public class EmptySelectListException extends IllegalStateException {
+	public EmptySelectListException() {
+		super("SELECT does not declare a select list");
+	}
+}

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/SelectValidator.java

@@ -54,7 +54,7 @@ private void doValidate(Select select) {
 		select.visit(this);
 
 		if (selectFieldCount == 0) {
-			throw new IllegalStateException("SELECT does not declare a select list");
+			throw new EmptySelectListException();
 		}
 
 		for (TableLike table : requiredBySelect) {