Exclude DTO types without custom construction from DTO constructor rewriting.

We now verify that we can actually express a valid constructor expression before rewriting queries to use constructor expressions.

See #3929

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/AbstractStringBasedJpaQuery.java

@@ -145,7 +145,7 @@ abstract class AbstractStringBasedJpaQuery extends AbstractJpaQuery {
 	ReturnedType getReturnedType(ResultProcessor processor) {
 
 		ReturnedType returnedType = processor.getReturnedType();
-		Class<?> returnedJavaType = processor.getReturnedType().getReturnedType();
+		Class<?> returnedJavaType = returnedType.getReturnedType();
 
 		if (!returnedType.isProjecting() || returnedJavaType.isInterface() || query.isNativeQuery()) {
 			return returnedType;
@@ -157,7 +157,8 @@ abstract class AbstractStringBasedJpaQuery extends AbstractJpaQuery {
 			return returnedType;
 		}
 
-		if ((known != null && !known) || returnedJavaType.isArray() || getMetamodel().isJpaManaged(returnedJavaType)) {
+		if ((known != null && !known) || returnedJavaType.isArray() || getMetamodel().isJpaManaged(returnedJavaType)
+				|| !returnedType.needsCustomConstruction()) {
 			if (known == null) {
 				knownProjections.put(returnedJavaType, false);
 			}

spring-data-jpa/src/test/java/org/springframework/data/jpa/domain/sample/Country.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2025 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.jpa.domain.sample;
+
+/**
+ * @author Mark Paluch
+ */
+public class Country {
+
+	private final String code;
+
+	// workaround to avoid DTO projections as needsCustomConstruction is false.
+	private Country(Country other) {
+		this.code = other.code;
+	}
+
+	private Country(String code) {
+		this.code = code;
+	}
+
+	public static Country of(String code) {
+		return new Country(code);
+	}
+
+	public String getCode() {
+		return code;
+	}
+}

spring-data-jpa/src/test/java/org/springframework/data/jpa/domain/sample/Customer.java

@@ -25,7 +25,7 @@ import jakarta.persistence.Id;
 @Entity
 public class Customer {
 
-    @Id Long id;
+	@Id Long id;
 
-    String name;
+		String name;
 }

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/RepositoryWithCompositeKeyTests.java

@@ -15,7 +15,7 @@
  */
 package org.springframework.data.jpa.repository;
 
-import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.*;
 
 import jakarta.persistence.EntityManager;
 
@@ -25,6 +25,7 @@ import java.util.List;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
+
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
@@ -115,6 +116,24 @@ class RepositoryWithCompositeKeyTests {
 		assertThat(persistedEmp.getDepartment().getName()).isEqualTo(dep.getName());
 	}
 
+	@Test // GH-3929
+	void shouldReturnIdentifiers() {
+
+		EmbeddedIdExampleDepartment dep = new EmbeddedIdExampleDepartment();
+		dep.setName("TestDepartment");
+		dep.setDepartmentId(-1L);
+
+		EmbeddedIdExampleEmployee emp = new EmbeddedIdExampleEmployee();
+		emp.setDepartment(dep);
+		emp.setEmployeePk(new EmbeddedIdExampleEmployeePK(1L, 2L));
+
+		emp = employeeRepositoryWithEmbeddedId.save(emp);
+
+		List<EmbeddedIdExampleEmployeePK> identifiers = employeeRepositoryWithEmbeddedId.findIdentifiers();
+
+		assertThat(identifiers).hasSize(1).contains(emp.getEmployeePk());
+	}
+
 	@Test // DATAJPA-472, DATAJPA-912
 	void shouldSupportFindAllWithPageableAndEntityWithIdClass() {
 

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/query/SimpleJpaQueryUnitTests.java

@@ -45,6 +45,7 @@ import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.Sort;
+import org.springframework.data.jpa.domain.sample.Country;
 import org.springframework.data.jpa.domain.sample.User;
 import org.springframework.data.jpa.provider.QueryExtractor;
 import org.springframework.data.jpa.repository.NativeQuery;
@@ -325,6 +326,17 @@ class SimpleJpaQueryUnitTests {
 		assertThatIllegalArgumentException().isThrownBy(() -> createJpaQuery(illegalMethod));
 	}
 
+	@Test // GH-3929
+	void doesNotRewriteQueryForDtoWithMultipleConstructors() throws Exception {
+
+		AbstractStringBasedJpaQuery jpaQuery = (AbstractStringBasedJpaQuery) createJpaQuery(
+				SampleRepository.class.getMethod("justCountries"));
+
+		String queryString = createQuery(jpaQuery);
+
+		assertThat(queryString).startsWith("select u.country from User u");
+	}
+
 	@Test // DATAJPA-1163
 	void resolvesExpressionInCountQuery() throws Exception {
 
@@ -408,6 +420,9 @@ class SimpleJpaQueryUnitTests {
 		@Query("select r.name from User u LEFT JOIN FETCH u.roles r")
 		Collection<UnrelatedType> projectWithJoinPaths();
 
+		@Query("select u.country from User u")
+		Collection<Country> justCountries();
+
 		@Query(value = "select u from #{#entityName} u", countQuery = "select count(u.id) from #{#entityName} u")
 		List<User> findAllWithExpressionInCountQuery(Pageable pageable);
 

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/sample/EmployeeRepositoryWithEmbeddedId.java

@@ -21,6 +21,7 @@ import org.springframework.context.annotation.Lazy;
 import org.springframework.data.jpa.domain.sample.EmbeddedIdExampleEmployee;
 import org.springframework.data.jpa.domain.sample.EmbeddedIdExampleEmployeePK;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.querydsl.QuerydslPredicateExecutor;
 
 import com.querydsl.core.types.OrderSpecifier;
@@ -40,6 +41,9 @@ public interface EmployeeRepositoryWithEmbeddedId
 	@Override
 	List<EmbeddedIdExampleEmployee> findAll(Predicate predicate, OrderSpecifier<?>... orders);
 
+	@Query("select e.employeePk from EmbeddedIdExampleEmployee e")
+	List<EmbeddedIdExampleEmployeePK> findIdentifiers();
+
 	// DATAJPA-920
 	boolean existsByName(String name);
 }