GH-2276 - Support default, primitive Kotlin attributes.

This bugfix allows primitive attributes with defaults in Kotlin based domain classes. It comes at a price however: We cannot throw a mapping exception hinting at the fact a primitive had been tried to be assigned with null in standard java. The ` MappingException`’s cause will than be a `NullpointerException`.

The value of supporting Kotlin defaults is in this case higher than the error message, which was "received" with a trick anyway (relying on the conversion service that it throws an exception.

This fixes #2276.

Author: michael-simons

src/main/java/org/springframework/data/neo4j/core/mapping/DefaultNeo4jConversionService.java

@@ -90,10 +90,9 @@ private Object readValueImpl(@Nullable Value value, TypeInformation<?> type,
 						.forEach(element -> target.add(conversion.apply(element, type.getComponentType().getType())));
 				return target;
 			}
-
-			return conversion.apply(valueIsLiteralNullOrNullValue ? null : value, rawType);
+			return valueIsLiteralNullOrNullValue ? null : conversion.apply(value, rawType);
 		} catch (Exception e) {
-			String msg = String.format("Could not convert %s into %s", value, type.toString());
+			String msg = String.format("Could not convert %s into %s", value, type);
 			throw new TypeMismatchDataAccessException(msg, e);
 		}
 	}

src/test/java/org/springframework/data/neo4j/integration/conversion_imperative/TypeConversionIT.java

@@ -110,9 +110,8 @@ void thereShallBeNoDefaultValuesForNonExistingAttributes(@Autowired NonExistingP
 				.isThrownBy(() -> repository.findById(ID_OF_NON_EXISTING_PRIMITIVES_NODE))
 				.withMessageMatching(
 						"Error mapping Record<\\{n: \\{__internalNeo4jId__: \\d+, id: NULL, someBoolean: NULL, __nodeLabels__: \\[\"NonExistingPrimitives\"\\]\\}\\}>")
-				.withStackTraceContaining(
-						"org.springframework.dao.TypeMismatchDataAccessException: Could not convert NULL into boolean; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [null] to type [boolean] for value 'null'; nested exception is java.lang.IllegalArgumentException: A null value cannot be assigned to a primitive type")
-				.withRootCauseInstanceOf(IllegalArgumentException.class);
+				.withStackTraceContaining("unboxBoolean")
+				.withRootCauseInstanceOf(NullPointerException.class);
 	}
 
 	@TestFactory

src/test/java/org/springframework/data/neo4j/integration/kotlin/KotlinIT.java

@@ -31,6 +31,8 @@
 import org.springframework.data.neo4j.integration.shared.common.KotlinClubRelationship;
 import org.springframework.data.neo4j.integration.shared.common.KotlinPerson;
 import org.springframework.data.neo4j.integration.shared.common.KotlinRepository;
+import org.springframework.data.neo4j.integration.shared.common.TestPersonEntity;
+import org.springframework.data.neo4j.integration.shared.common.TestPersonRepository;
 import org.springframework.data.neo4j.repository.config.EnableNeo4jRepositories;
 import org.springframework.data.neo4j.test.Neo4jExtension.Neo4jConnectionSupport;
 import org.springframework.data.neo4j.test.Neo4jIntegrationTest;
@@ -60,6 +62,11 @@ void setup() {
 					+ " (n)-[:WORKS_IN{since: 2019}]->(:KotlinClub{name: 'Golf club'}) SET n.name = $personName",
 					Values.parameters("personName", PERSON_NAME))
 					.consume();
+			transaction.run("CREATE (p1:TestPerson {id: \"first\", name: \"First name\"})\n"
+							+ "CREATE (p2:TestPerson {id: \"second\"})\n"
+							+ "CREATE (d:TestDepartment {id: \"department\", name: \"Test\"})\n"
+							+ "CREATE (p1)-[:MEMBER_OF]->(d)\n"
+							+ "CREATE (p2)-[:MEMBER_OF]->(d)\n").consume();
 			transaction.commit();
 		}
 	}
@@ -75,6 +82,22 @@ void findAllKotlinPersons(@Autowired KotlinRepository repository) {
 				.extracting(KotlinClub::getName).containsExactly("Golf club");
 	}
 
+	@Test // GH-2272
+	void primitiveDefaultValuesShouldWork(@Autowired TestPersonRepository repository) {
+
+		Iterable<TestPersonEntity> people = repository.findAll();
+		assertThat(people)
+				.allSatisfy(p -> {
+					assertThat(p.getOtherPrimitive()).isEqualTo(32);
+					assertThat(p.getSomeTruth()).isTrue();
+					if (p.getId().equalsIgnoreCase("first")) {
+						assertThat(p.getName()).isEqualTo("First name");
+					} else {
+						assertThat(p.getName()).isEqualTo("Unknown");
+					}
+				});
+	}
+
 	@Configuration
 	@EnableNeo4jRepositories(basePackageClasses = KotlinPerson.class)
 	@EnableTransactionManagement

src/test/kotlin/org/springframework/data/neo4j/integration/shared/common/TestPersonEntity.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2011-2021 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.neo4j.integration.shared.common
+
+import org.springframework.data.neo4j.core.schema.Id
+import org.springframework.data.neo4j.core.schema.Node
+import org.springframework.data.neo4j.core.schema.Property
+import org.springframework.data.neo4j.repository.Neo4jRepository
+
+@Node("TestPerson")
+data class TestPersonEntity(
+		@Id
+		val id: String,
+		@Property("name")
+		val name: String = "Unknown",
+		val otherPrimitive: Int = 32,
+		val someTruth: Boolean = true
+)
+
+interface TestPersonRepository : Neo4jRepository<TestPersonEntity, String> {
+}