问题：
Spring JPA实体在向其他实体添加相同项目时丢失数据
卢恩
使用Java1.8，Spring Boot，JPA，我创建了一个Spring Boot微服务，其中数据模型（实体关系）遵循这个特定的一对多关系：
Owner can have many Cars.
Cars only have one Owner.
此Spring Boot Microservice具有以下功能：
HTTP获取endpoint：
- 从数据库中获取特定所有者的数据（姓名、地址等）
- 从数据库中检索特定车主的汽车信息（品牌、型号等）
HTTP POSTendpoint：
- 将Owner的数据保存到数据库中。
- 将车主汽车的数据存入数据库。
当我运行springbootmicroservice并手动创建所有者时，这些都可以工作
我现在要做的是在SpringBootMicroService加载时填充这些测试（这样，我可以在Maven构建完成之前开始编写单元测试和集成测试）。
为此，我创建了以下文件：
@Component
public class DataInserter implements ApplicationListener<ContextRefreshedEvent> {
@Value("classpath:data/owners.json")
Resource ownersResource;
@Value("classpath:data/cars.json")
Resource carsResource;
@Autowired
private OwnerService ownerService;
@Autowired
private CarsService carService;
@Override
public void onApplicationEvent(ContextRefreshedEvent contextRefreshedEvent) {
List<Owner> populatedOwners = new ArrayList<>();
try {
Owner aOwner;
File ownersFile = ownersResource.getFile();
File carsFile = carsResource.getFile();
String ownersString = new String(Files.readAllBytes(ownersFile.toPath()));
String carsString = new String(Files.readAllBytes(carsFile.toPath()));
ObjectMapper mapper = new ObjectMapper();
List<Owner> owners = Arrays.asList(mapper.readValue(ownersString, Owner[].class));
List<ElectricCars> cars = Arrays.asList(mapper.readValue(carsString, ElectricCars[].class));
// Populate owners one by one
for (Owner owner : owners) {
aOwner = new Owner(owner.getName(), owner.getAddress(), owner.getCity(), owner.getState(), owner.getZipCode());
ownerService.createOwner(aOwner);
populatedOwners.add(aOwner);
}
// Populate owner cars one by one
for (int i = 0; i < populatedOwners.size(); i++) {
carService.createCars(populatedOwners.get(i).getId(), cars.get(i));
}
// Provide some owners with multiple cars
// carService.createCars(populatedOwners.get(0).getId(), cars.get(3));
// carService.createCars(populatedOwners.get(0).getId(), cars.get(4));
// carService.createCars(populatedOwners.get(1).getId(), cars.get(3));
}
catch(IOException ioe) {
ioe.printStackTrace();;
}
}
}
src/main/resources/data/cars。json:
[
{
"make": "Honda",
"model": "Accord",
"year": "2020"
},
{
"make": "Nissan",
"model": "Maxima",
"year": "2019"
},
{
"make": "Toyota",
"model": "Prius",
"year": "2015"
},
{
"make": "Porsche",
"model": "911",
"year": "2017"
},
{
"make": "Hyundai",
"model": "Elantra",
"year": "2018"
},
{
"make": "Volkswagen",
"model": "Beatle",
"year": "1973"
},
{
"make": "Ford",
"model": "F-150",
"year": "2010"
},
{
"make": "Chevrolet",
"model": "Silverado",
"year": "2020"
},
{
"make": "Toyota",
"model": "Camary",
"year": "2018"
},
{
"make": "Alfa",
"model": "Romeo",
"year": "2017"
}
]
src/main/resources/data/owner。json:
[
{
"name": "Tom Brady"
},
{
"name": "Kobe Bryant"
},
{
"name": "Mike Tyson"
},
{
"name": "Scottie Pippen"
},
{
"name": "John Madden"
},
{
"name": "Arnold Palmer"
},
{
"name": "Tiger Woods"
},
{
"name": "Magic Johnson"
},
{
"name": "George Foreman"
},
{
"name": "Charles Barkley"
}
]
因此，当我运行此程序时，以下几行被注释掉：
// Populate owner cars one by one
for (int i = 0; i < populatedOwners.size(); i++) {
carService.createCars(populatedOwners.get(i).getId(), cars.get(i));
}
// Provide some owners with multiple cars
// carService.createCars(populatedOwners.get(0).getId(), cars.get(3));
// carService.createCars(populatedOwners.get(0).getId(), cars.get(4));
// carService.createCars(populatedOwners.get(1).getId(), cars.get(3));
然后我调用我的Get All Owners RESTendpoint（请参见下文）：
获取http://localhost:8080/car-api/所有者
JSON有效载荷正确输出（每个车主都有一辆车）：
[
{
"id": 1,
"name": "Tom Brady",
"cars": [
{
"id": 1,
"make": "Honda",
"model": "Accord",
"year": "2020"
}
]
},
{
"id": 2,
"name": "Kobe Bryant",
"cars": [
{
"id": 2,
"make": "Nissan",
"model": "Maxima",
"year": "2019"
}
]
},
{
"id": 3,
"name": "Mike Tyson",
"cars": [
{
"id": 3,
"make": "Toyota",
"model": "Prius",
"year": "2015"
}
]
},
{
"id": 4,
"name": "Scottie Pippen",
"cars": [
{
"id": 4,
"make": "Porsche",
"model": "911",
"year": "2017"
}
]
},
{
"id": 5,
"name": "John Madden",
"cars": [
{
"id": 5,
"make": "Hyundai",
"model": "Elantra",
"year": "2018"
}
]
},
{
"id": 6,
"name": "Arnold Palmer",
"cars": [
{
"id": 6,
"make": "Volkswagen",
"model": "Beatle",
"year": "1973"
}
]
},
{
"id": 7,
"name": "Tiger Woods",
"cars": [
{
"id": 7,
"make": "Ford",
"model": "F-150",
"year": "2010"
}
]
},
{
"id": 8,
"name": "Magic Johnson",
"cars": [
{
"id": 8,
"make": "Chevrolet",
"model": "Silverado",
"year": "2020"
}
]
},
{
"id": 9,
"name": "George Foreman",
"cars": [
{
"id": 9,
"make": "Toyota",
"model": "Camary",
"year": "2018"
}
]
},
{
"id": 10,
"name": "Charles Barkley",
"cars": [
{
"id": 10,
"make": "Alfa",
"model": "Romeo",
"year": "2017"
}
]
}
]
但是，当我尝试将更多汽车分配给个人车主时（这似乎会导致其他车主的汽车JSON数组变为空）：
// Populate owner cars one by one
for (int i = 0; i < populatedOwners.size(); i++) {
carService.createCars(populatedOwners.get(i).getId(), cars.get(i));
}
// Provide some owners with multiple cars
carService.createCars(populatedOwners.get(0).getId(), cars.get(3));
carService.createCars(populatedOwners.get(0).getId(), cars.get(4));
carService.createCars(populatedOwners.get(1).getId(), cars.get(3));
JSON有效负载产生以下结果：
[
{
"id": 1,
"name": "Tom Brady",
"cars": [
{
"id": 1,
"make": "Honda",
"model": "Accord",
"year": "2020"
},
{
"id": 5,
"make": "Hyundai",
"model": "Elantra",
"year": "2018"
}
]
},
{
"id": 2,
"name": "Kobe Bryant",
"cars": [
{
"id": 2,
"make": "Nissan",
"model": "Maxima",
"year": "2019"
},
{
{
"id": 4,
"make": "Porsche",
"model": "911",
"year": "2017"
}
]
},
{
"id": 3,
"name": "Mike Tyson",
"cars": [
{
"id": 3,
"make": "Toyota",
"model": "Prius",
"year": "2015"
}
]
},
{
"id": 4,
"name": "Scottie Pippen",
"cars": []
},
{
"id": 5,
"name": "John Madden",
"cars": []
},
{
"id": 6,
"name": "Arnold Palmer",
"cars": [
{
"id": 6,
"make": "Volkswagen",
"model": "Beatle",
"year": "1973"
}
]
},
{
"id": 7,
"name": "Tiger Woods",
"cars": [
{
"id": 7,
"make": "Ford",
"model": "F-150",
"year": "2010"
}
]
},
{
"id": 8,
"name": "Magic Johnson",
"cars": [
{
"id": 8,
"make": "Chevrolet",
"model": "Silverado",
"year": "2020"
}
]
},
{
"id": 9,
"name": "George Foreman",
"cars": [
{
"id": 9,
"make": "Toyota",
"model": "Camary",
"year": "2018"
}
]
},
{
"id": 10,
"name": "Charles Barkley",
"cars": [
{
"id": 10,
"make": "Alfa",
"model": "Romeo",
"year": "2017"
}
]
}
]
正如你所看到的，这些汽车似乎被添加到汤姆·布拉迪和科比·布莱恩特的JSON系列汽车中，但从拥有它们的人那里删除了（斯科蒂·皮蓬
为什么会发生这种情况，这是我的carserviceinpl可能存在的错误吗。createCar（）方法？
波姆。xml:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.2.5.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.myapi</groupId>
<artifactId>car-api</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>car-api</name>
<description>Car REST API</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jdbc</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
<exclusions>
<exclusion>
<groupId>org.junit.vintage</groupId>
<artifactId>junit-vintage-engine</artifactId>
</exclusion>
</exclusions>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
src/main/resources/applications。特性：
server.servlet.context-path=/car-api
server.port=8080
server.error.whitelabel.enabled=false
# Database specific
spring.jpa.hibernate.ddl-auto=create
spring.datasource.url=jdbc:mysql://localhost:3306/car_db?useSSL=false
spring.datasource.ownername=root
spring.datasource.password=
业主单位：
@Entity
@Table(name = "owner")
public class Owner {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@NotNull
private String name;
@OneToMany(cascade = CascadeType.ALL,
fetch = FetchType.EAGER,
mappedBy = "owner")
private List<Car> cars = new ArrayList<>();
public Owner() {
}
// Getter & Setters omitted for brevity.
}
汽车实体：
@Entity
@Table(name="car")
public class Car {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
String make;
String model;
String year;
@JsonIgnore
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "owner_id", nullable = false)
private Owner owner;
// Getter & Setters omitted for brevity.
}
业主地址：
@Repository
public interface OwnerRepository extends JpaRepository<Owner, Long> {
}
随身携带：
@Repository
public interface CarRepository extends JpaRepository<Car, Long> {
}
业主服务：
public interface OwnerService {
boolean createOwner(Owner owner);
Owner getOwnerByOwnerId(Long ownerId);
List<Owner> getAllOwners();
}
OwnerServiceImpl：
@Service
public class OwnerServiceImpl implements OwnerService {
@Autowired
OwnerRepository ownerRepository;
@Autowired
CarRepository carRepository;
@Override
public List<Owner> getAllOwners() {
return ownerRepository.findAll();
}
@Override
public boolean createOwner(Owner owner) {
boolean created = false;
if (owner != null) {
ownerRepository.save(owner);
created = true;
}
return created;
}
@Override
public Owner getOwnerByOwnerId(Long ownerId) {
Optional<Owner> owner = null;
if (ownerRepository.existsById(ownerId)) {
owner = ownerRepository.findById(ownerId);
}
return owner.get();
}
}
汽车服务：
public interface CarService {
boolean createCar(Long ownerId, Car car);
}
CarServiceImpl：
@Service
public class CarServiceImpl implements CarService {
@Autowired
OwnerRepository ownerRepository;
@Autowired
CarRepository carRepository;
@Override
public boolean createCar(Long ownerId, Car car) {
boolean created = false;
if (ownerRepository.existsById(ownerId)) {
Optional<Owner> owner = ownerRepository.findById(ownerId);
if (owner != null) {
List<Car> cars = owner.get().getCars();
cars.add(car);
owner.get().setCars(cars);
car.setOwner(owner.get());
carRepository.save(car);
created = true;
}
}
return created;
}
}
OwnerController：
@RestController
public class OwnerController {
private HttpHeaders headers = null;
@Autowired
OwnerService ownerService;
public OwnerController() {
headers = new HttpHeaders();
headers.add("Content-Type", "application/json");
}
@RequestMapping(value = { "/owners" }, method = RequestMethod.POST, produces = "APPLICATION/JSON")
public ResponseEntity<Object> createOwner(@Valid @RequestBody Owner owner) {
boolean isCreated = ownerService.createOwner(owner);
if (isCreated) {
return new ResponseEntity<Object>(headers, HttpStatus.OK);
}
else {
return new ResponseEntity<Object>(HttpStatus.NOT_FOUND);
}
}
@RequestMapping(value = { "/owners" }, method = RequestMethod.GET, produces = "APPLICATION/JSON")
public ResponseEntity<Object> getAllOwners() {
List<Owner> owners = ownerService.getAllOwners();
if (owners.isEmpty()) {
return new ResponseEntity<Object>(HttpStatus.NOT_FOUND);
}
return new ResponseEntity<Object>(owners, headers, HttpStatus.OK);
}
@RequestMapping(value = { "/owners/{ownerId}" }, method = RequestMethod.GET, produces = "APPLICATION/JSON")
public ResponseEntity<Object> getOwnerByOwnerId(@PathVariable Long ownerId) {
if (null == ownerId || "".equals(ownerId)) {
return new ResponseEntity<Object>(HttpStatus.NOT_FOUND);
}
Owner owner = ownerService.getOwnerByOwnerId(ownerId);
return new ResponseEntity<Object>(owner, headers, HttpStatus.OK);
}
}
车辆控制员：
@RestController
public class CarController {
private HttpHeaders headers = null;
@Autowired
CarService carService;
public CarController() {
headers = new HttpHeaders();
headers.add("Content-Type", "application/json");
}
@RequestMapping(value = { "/cars/{ownerId}" }, method = RequestMethod.POST, produces = "APPLICATION/JSON")
public ResponseEntity<Object> createCarBasedOnOwnerId(@Valid @RequestBody Car car, Long ownerId) {
boolean isCreated = carService.createCar(ownerId, car);
if (isCreated) {
return new ResponseEntity<Object>(headers, HttpStatus.OK);
}
else {
return new ResponseEntity<Object>(HttpStatus.NOT_FOUND);
}
}
问题:
>
注意到里面的主人。java，我必须创建FetchType。急切的：
@OneToMany(cascade = CascadeType.ALL,
fetch = FetchType.EAGER,
mappedBy = "owner")
private List<Car> cars = new ArrayList<>();
当我把它设为fetch=FetchType时。LAZY它引发了以下异常：
2020-03-08 15:18:13,175 ERROR org.springframework.boot.SpringApplication [main] Application run failed
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.myapi.model.User.cars, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:606)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:218)
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:585)
at org.hibernate.collection.internal.AbstractPersistentCollection.write(AbstractPersistentCollection.java:409)
at org.hibernate.collection.internal.PersistentBag.add(PersistentBag.java:407)
at org.hibernate.collection.internal.PersistentBag.add(PersistentBag.java:407)
at com.myapi.service.CarServiceImpl.createCar(CarServiceImpl.java:36)
at com.myapi.bootstrap.DataInserter.onApplicationEvent(DataInserter.java:71)
at com.myapi.bootstrap.DataInserter.onApplicationEvent(DataInserter.java:24)
at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:403)
at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:360)
at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:897)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.finishRefresh(ServletWebServerApplicationContext.java:162)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:553)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
at com.myapi.CarApplication.main(CarApplication.java:12)
这是相关的还是单独的问题？我对JPA有些陌生，所以我想知道是否需要更改cascade=CascadeType的值。两个实体中的所有都指向其他实体。
共有2个答案
陆烨磊
DataInserter的问题是，它使用相同的汽车对象将其重新分配给不同的车主。如果我们想将多辆车分配给车主，我们需要比车主拥有更多的车对象。我们需要克隆汽车对象以创建具有相同属性的不同汽车对象。
我们可以在Car类中编写copy构造函数，它接受现有的Car并返回具有相同属性的Car的副本或克隆。因此，我们可以使用现有的汽车对象创建新的汽车对象。例如，如下所示
Car newCarObject = new Car(existingCarObject);
并修改以下代码以使用现有汽车对象创建新汽车对象。
// Provide some owners with multiple cars
// carService.createCars(populatedOwners.get(0).getId(), new Car(cars.get(3)));
// carService.createCars(populatedOwners.get(0).getId(), new Car(cars.get(4)));
// carService.createCars(populatedOwners.get(1).getId(), new Car(cars.get(3)));
梁宏才
- 为什么通过向Owner的汽车ArrayList添加新车，它会删除其他Owner的汽车（具有相同的car.id）？
因为你已经把它编好了。这就是你如何定义汽车和车主之间的关系：
汽车只有一个主人。
那么如何让汽车拥有多个车主呢？如果你想多次拥有同一辆车，你必须用相同的数据创建一个新实体（除了id）。
2.异常
hibernate中的X-to-many关系（一对多、多对多）总是以惰性方式获取。这意味着，当您获取具有对多关系的实体时，出于性能原因，不会获取集合。如果您尝试对其进行迭代，将抛出LazyInitializationException。使用FetchType进行注释。急切的是一个解决方案，但不是一个好的解决方案，因为无论是否需要，都会获取集合。更好的方法是在存储库中使用例如jpql：
@Query("select o from Owner o where o.id = :id left join fetch o.cars")
findOrderWithCars(@Param("id") Long ownerId)
对例如，使用flyway就是这样一种解决方案。您只需要创建sql脚本，用数据填充html" target="_blank">数据库并配置数据源。您不必编写那么多代码、映射json对象等。
附带说明：此代码是一个杀手：
if (ownerRepository.existsById(ownerId)) {
Optional<Owner> owner = ownerRepository.findById(ownerId);
if (owner != null) {
List<Car> cars = owner.get().getCars();
cars.add(car);
owner.get().setCars(cars);
car.setOwner(owner.get());
carRepository.save(car);
created = true;
}
}
首先，检查数据库中是否存在该实体，如果存在，则向数据库发射另一枪以获取该实体。它可以在一次往返中完成。另一个问题是，您正在检查可选是否为空<代码>可选不应为null。您可能想编写owner。isPresent（）。
类似资料：
-
若要添加一个新的实体，点击工具栏的 按钮，并点击画布的任意位置。你可以从浏览器的模型选项卡添加一个现有的实体，简单地从模型选项卡拖放实体到画布。 在画布中实体对象的弹出式菜单选项包括： 选项 描述 添加关联的对象 添加全部关联的实体到选择的实体。 剪切 从图表移除实体并放它在剪贴板。 复制 从图表复制实体到剪贴板。 粘贴 将剪贴板的内容贴到图表。 选择全部实体 在图表中选择全部实体。 删除 从图表
-
若要添加一个新的实体，点击工具栏的 按钮，并点击画布的任意位置。你可以从浏览器的模型选项卡添加一个现有的实体，简单地从模型选项卡拖放实体到画布。 如果图表符号设置为默认， 图标代表属性为一个主键。而 图标则代表属性为一个索引。 【注意】如果你右击属性，你可以选择添加、插入、删除、重命名属性及设置属性为主键。 在画布中实体对象的弹出式菜单选项包括： 选项 描述 设计实体 在实体设计器中编辑实体结构，
-
若要添加一个新的实体，点击工具栏的 按钮，并点击画布的任意位置。你可以从浏览器的模型选项卡添加一个现有的实体，简单地从模型选项卡拖放实体到画布。 在画布中实体对象的弹出式菜单选项包括： 选项 描述 添加关联的对象 添加全部关联的实体到选择的实体。 剪切 从图表移除实体并放它在剪贴板。 复制 从图表复制实体到剪贴板。 粘贴 将剪贴板的内容贴到图表。 选择全部实体 在图表中选择全部实体。 删除 从图表
-
若要添加一个新的实体，点击工具栏的 按钮，并点击画布的任意位置。你可以从浏览器的模型选项卡添加一个现有的实体，简单地从模型选项卡拖放实体到画布。 如果图表符号设置为默认， 图标代表属性为一个主键。而 图标则代表属性为一个索引。 【注意】如果你按住 Control 键并点按属性，你可以选择添加、插入、删除、重命名属性及设置属性为主键。 在画布中实体对象的弹出式菜单选项包括： 选项 描述 设计实体 在
-
若要添加一个新的实体，点击工具栏的 按钮，并点击画布的任意位置。你可以从浏览器的模型选项卡添加一个现有的实体，简单地从模型选项卡拖放实体到画布。 在画布中实体对象的弹出式菜单选项包括： 选项 描述 添加关联的对象 添加全部关联的实体到选择的实体。 剪切 从图表移除实体并放它在剪贴板。 复制 从图表复制实体到剪贴板。 粘贴 将剪贴板的内容贴到图表。 选择全部实体 在图表中选择全部实体。 删除 从图表
-
若要添加一个新的实体，点击工具栏的 按钮，并点击画布的任意位置。你可以从浏览器的模型选项卡添加一个现有的实体，简单地从模型选项卡拖放实体到画布。 如果图表符号设置为默认， 图标代表属性为一个主键。而 图标则代表属性为一个索引。 【注意】如果你右击属性，你可以选择添加、插入、删除、重命名属性及设置属性为主键。 在画布中实体对象的弹出式菜单选项包括： 选项 描述 设计实体 在实体设计器中编辑实体结构，