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Hibernate通过外键获取没有属性的实体列表

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我想通过连接它们的特定corporate_id从任务表中检索任务实体的列表。我似乎遇到的问题是，由于Hibernate查看没有corporate_id属性的类，因此找不到corporate_id列。有什么办法可以解决这个问题？

我已经尝试创建一个corporate_id属性，但这给了我一个NullPointerException。

我有一个CorporateEvent班：

@Entity
@Table(name="corporate_event")
public class CorporateEvent extends Event {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "id_generator")
    @SequenceGenerator(name = "id_generator",sequenceName = "corporate_event_id_seq",allocationSize = 1)
    @Column(name = "corporate_id",updatable = false,nullable = false)
    private int id;

    @OneToMany(cascade=CascadeType.ALL,mappedBy="corporateEvent")
    private List<Task> tasks;

和一个Task类：

@Entity
@Table(name="task")
public class Task {

  @Id
  @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "id_generator")
  @SequenceGenerator(name="id_generator",sequenceName = "task_task_id_seq",allocationSize=1)
  @Column(name="task_id",nullable = false)
  private int id;

  @ManyToOne
  @JoinColumn(name="corporate_id")
  private CorporateEvent corporateEvent;

  @Column(name="name")
  private String taskName;

  @Column(name="description")
  private String description;

这是到目前为止我尝试过的Hibernate方法：

public List<Task> getTasksByCorporateEvent(CorporateEvent corporateEvent){
       session = ConnectRepository.factory.getcurrentSession();
       session.beginTransaction();

       CriteriaBuilder criteriaBuilder = session.getcriteriaBuilder();
       CriteriaQuery<Task> criteriaQuery = criteriaBuilder.createQuery(Task.class);
       Root<Task> root = criteriaQuery.from(Task.class);

      criteriaQuery.select(root).where(criteriaBuilder.equal(root.get("corporateEvent.corporateID"),corporateEvent.getId()));
      Query<Task> query = session.createQuery(criteriaQuery);
      List result = query.getResultList();

这：

List<Task> result = session.createQuery("SELECT t FROM Task t WHERE t.corporate_id = :id").setParameter("id",corporateEvent.getId()).getResultList();

这些是两个类上的数据库表：

CorporateEvent表：

create table corporate_event
(
    title            varchar,date             varchar(1000),location         varchar,description      varchar,max_participants integer,expenses         varchar(2000),corporate_id     serial not null
        constraint corporate_event_pk
            primary key,tasks            varchar(4000)
);

alter table corporate_event
    owner to si3_2019_group_5;

create unique index corporate_event_id_uindex
    on corporate_event (corporate_id);

Task表：

create table task
(
    task_id      serial not null constraint task_pk primary key,name         varchar,description  varchar(1000),corporate_id integer
        constraint corporate_id
            references corporate_event
            on update cascade on delete cascade
);

alter table task owner to si3_2019_group_5;

create unique index task_task_id_index on task (task_id);

更新 添加了Obi-Wan所做的更正后，我无法再保存对象。这是堆栈跟踪：

------------------------------------------------------------------------
Building Eventer 1.0-snAPSHOT
------------------------------------------------------------------------

--- maven-resources-plugin:2.5:resources (default-resources) @ Eventer ---
[debug] execute contextualize
Using 'UTF-8' encoding to copy filtered resources.
Copying 11 resources

--- maven-compiler-plugin:3.6.1:compile (default-compile) @ Eventer ---
Nothing to compile - all classes are up to date

--- exec-maven-plugin:1.2.1:exec (default-cli) @ Eventer ---
Nov 18,2019 1:10:45 PM org.hibernate.Version logVersion
INFO: HHH000412: Hibernate Core {5.4.8.Final}
Nov 18,2019 1:10:45 PM org.hibernate.annotations.common.reflection.java.JavaReflectionmanager <clinit>
INFO: HCANN000001: Hibernate Commons Annotations {5.1.0.Final}
Nov 18,2019 1:10:46 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl configure
WARN: HHH10001002: Using Hibernate built-in connection pool (not for production use!)
Nov 18,2019 1:10:46 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001005: using driver [org.postgresql.Driver] at URL [jdbc:postgresql://tek-mmmi-db0a.tek.c.sdu.dk:5432/si3_2019_group_5_db]
Nov 18,2019 1:10:46 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001001: Connection properties: {user=si3_2019_group_5,password=****}
Nov 18,2019 1:10:46 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl buildCreator
INFO: HHH10001003: Autocommit mode: false
Nov 18,2019 1:10:46 PM org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections <init>
INFO: HHH000115: Hibernate connection pool size: 1 (min=1)
Nov 18,2019 1:10:46 PM org.hibernate.dialect.Dialect <init>
INFO: HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
Nov 18,2019 1:10:50 PM org.hibernate.cfg.AnnotationBinder bindClass
WARN: HHH000503: A class should not be annotated with both @Inheritance and @MappedSuperclass. @Inheritance will be ignored for: com.mycompany.domain.event.Event.
Nov 18,2019 1:10:50 PM org.hibernate.boot.internal.InFlightMetadataCollectorImpl addIdentifierGenerator
WARN: HHH000069: Duplicate generator name id_generator
Nov 18,2019 1:10:50 PM org.hibernate.boot.internal.InFlightMetadataCollectorImpl addIdentifierGenerator
WARN: HHH000069: Duplicate generator name id_generator
Exception in thread "main" java.lang.NullPointerException
    at com.mycompany.repositories.EventRepository.saveCorporateEvent(EventRepository.java:57)
    at com.mycompany.domain.event.EventManager.createCorporateEvent(EventManager.java:30)
    at com.mycompany.eventer.Eventer.main(Eventer.java:64)
------------------------------------------------------------------------
BUILD FAILURE
------------------------------------------------------------------------
Total time: 7.987s
Finished at: Mon Nov 18 13:10:50 CET 2019
Final Memory: 9M/100M
------------------------------------------------------------------------
Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:exec (default-cli) on project Eventer: Command execution failed. Process exited with an error: 1 (Exit value: 1) -> [Help 1]

To see the full stack trace of the errors,re-run Maven with the -e switch.
Re-run Maven using the -X switch to enable full debug logging.

For more information about the errors and possible solutions,please read the following articles:
[Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

这是将corporateEvent保存到数据库方法：

public int saveCorporateEvent(CorporateEvent corporateEvent) {

        try {
            session = ConnectRepository.factory.getcurrentSession();
            session.beginTransaction();
            session.persist(corporateEvent);
            session.getTransaction().commit();
            return corporateEvent.getId();
        } catch (Exception e) {
            e.printStackTrace();

        } finally {
            session.close();
        }
        return 0;
    }

我还向@OneToMany(cascade=CascadeType.ALL,mappedBy="corporateEvent")类的OneToMany注释中添加了CorporateEvent，因为它给了我很多其他异常（重复的ID和“未保存的瞬态实例”）。

cycannon 回答：Hibernate通过外键获取没有属性的实体列表

您应将One to Many内部的CorporateEvent关系更新为

@OneToMany
@JoinColumn(name = "task_id")
private List<Task> tasks;

如果查询更改为

，createQuery应该可以使用

SELECT t FROM Task t WHERE t.corporateEvent.id = :id

但是此HQL将在Tasks和CorporateEvent之间建立联接。 为了删除联接，您可以在Task实体内创建一个新字段，以仅加载corporate_id而不是获取整个CorporateEvent对象。

@Basic
@Column(name = "corporate_id")
private Integer corporateEventId

然后，您可以使用此HQL

SELECT t FROM Task t WHERE t.corporateEventId = :id

hibernatejavamavenpostgresql
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