如果我有兩個以上的物體，我是否需要在JavaSpring中宣告一個entitymanagerfactory？

將我的 2 個資料庫表拆分為更合乎邏輯的表后，我最終擁有 6 個表，這些表是我在 Java 中作為物體實作的。

由于我實作了它們，因此在部署 Spring 應用程式時會出現 NullPointerException。

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-10-17 16:41:35.924 ERROR 8012 --- [  restartedMain] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init method failed; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1804) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:620) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1154) ~[spring-context-5.3.10.jar:5.3.10]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:908) ~[spring-context-5.3.10.jar:5.3.10]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.10.jar:5.3.10]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:434) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:338) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1343) ~[spring-boot-2.5.5.jar:2.5.5]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1332) ~[spring-boot-2.5.5.jar:2.5.5]
    at com.softwareprojekt.explorer.ExplorerApplication.main(ExplorerApplication.java:10) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.5.5.jar:2.5.5]
Caused by: java.lang.NullPointerException: null
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processFkSecondPassesInOrder(InFlightMetadataCollectorImpl.java:1745) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.processSecondPasses(InFlightMetadataCollectorImpl.java:1655) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:295) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:1224) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:1255) ~[hibernate-core-5.4.32.Final.jar:5.4.32.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:58) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:409) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:396) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) ~[spring-orm-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1863) ~[spring-beans-5.3.10.jar:5.3.10]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1800) ~[spring-beans-5.3.10.jar:5.3.10]
    ... 21 common frames omitted


Process finished with exit code 0

如果我有多個表，是否必須實作資料訪問物件？如果是，我如何在 Spring 中做到這一點？據我所知，Spring 在內部完成了這一切。

這些是我的一些物體 1。

@Entity
@Table(name="account")
public class Account implements Serializable{

@Id
private String address;

private String authentication_key;

private int sequence_number;

private boolean is_frozen;

@Entity
@Table(name="accountbalancexdx")
public class AccountBalanceXDX implements Serializable{

@Id
private String address;

private double amount;

@Entity
@Table(name="accountbalancexus")
public class AccountBalanceXUS implements Serializable{
@Id
@OneToOne
private String address;

private double amount;

目前還沒有 Controller 或 Repository。

編輯：我剛剛發現在使用 @OneToOne 之類的 ORM 注釋時出現錯誤。那么在 Spring 中，您不能使用這些注釋嗎？

我將非常感謝每一條有用的資訊。

uj5u.com熱心網友回復：

在此處使用 @OneToOne 是不正確的：

@Id
@OneToOne
private String address;

@OneToOne 用于物體，字串不是物體。所以你需要洗掉那個注釋

uj5u.com熱心網友回復：

基本上@OneToOne，@ManyToOneetc 通常用于在物體類中定義外鍵關系。話雖如此，這兩個注釋中的任何一個都應該采用物體而不是 String、Long 等。

Baeldung 所描述的類似這樣的事情：您的主表：

@Entity 
@Table(name = "users") 
 public class User {
    
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;
    //... 

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "address_id", referencedColumnName = "id")
    private Address address;

    // ... getters and setters 
 }

你的孩子/次要桌

@Entity
@Table(name = "address")
public class Address {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;
    //...

    @OneToOne(mappedBy = "address")
    private User user;

    //... getters and setters
}

更多資訊可以在這里找到

標籤：爪哇 春天 弹簧靴 休眠 休眠实体管理器

上一篇：即使出現例外，Hibernate如何提交事務

下一篇：NaukriApi更新簡歷