如果没有任何帮助，并且您仍然得到这个异常，请检查equals()方法—并且不要在其中包含子集合。特别是当你有嵌入式集合的深层结构时(例如A包含B, B包含c，等等)。

以Account ->为例:

  public class Account {

    private Long id;
    private String accountName;
    private Set<Transaction> transactions;

    @Override
    public boolean equals(Object obj) {
      if (this == obj)
        return true;
      if (obj == null)
        return false;
      if (!(obj instanceof Account))
        return false;
      Account other = (Account) obj;
      return Objects.equals(this.id, other.id)
          && Objects.equals(this.accountName, other.accountName)
          && Objects.equals(this.transactions, other.transactions); // <--- REMOVE THIS!
    }
  }

在上面的例子中，从equals()检查中删除事务。这是因为hibernate将暗示您不尝试更新旧对象，而是在更改子集合上的元素时传递一个新对象来持久化。 当然，这种解决方案并不适用于所有应用程序，您应该仔细设计想要包含在equals和hashCode方法中的内容。

在我的情况下，我正在提交事务时，持久化方法被使用。 在更改persist to save方法时，该问题得到了解决。

如果上述解决方案不工作，只需一次注释实体类的getter和setter方法，并且不设置id的值。(主键) 这样就可以了。

这里的问题是缺乏控制。

当我们使用CrudRepository/JPARepository保存方法时，我们失去了事务控制。

为了解决这个问题，我们有了事务管理

我更喜欢@Transactional机制

进口

import javax.transaction.Transactional;

完整源代码:

package com.oracle.dto;

import lombok.*;

import javax.persistence.*;
import java.util.Date;
import java.util.List;

@Entity
@Data
@ToString(exclude = {"employee"})
@EqualsAndHashCode(exclude = {"employee"})
public class Project {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO,generator = "ps")
    @SequenceGenerator(name = "ps",sequenceName = "project_seq",initialValue = 1000,allocationSize = 1)
    @Setter(AccessLevel.NONE)
    @Column(name = "project_id",updatable = false,nullable = false)
    private Integer pId;
    @Column(name="project_name",nullable = false,updatable = true)
    private String projectName;
    @Column(name="team_size",nullable = true,updatable = true)
    private Integer teamSize;
    @Column(name="start_date")
    private Date startDate;
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name="projectemp_join_table",
        joinColumns = {@JoinColumn(name = "project_id")},
        inverseJoinColumns = {@JoinColumn(name="emp_id")}
    )
    private List<Employee> employees;
}

package com.oracle.dto;

import lombok.*;

import javax.persistence.*;
import java.util.List;

@Entity
@Data
@EqualsAndHashCode(exclude = {"projects"})
@ToString(exclude = {"projects"})
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO,generator = "es")
    @SequenceGenerator(name = "es",sequenceName = "emp_seq",allocationSize = 1,initialValue = 2000)
    @Setter(AccessLevel.NONE)
    @Column(name = "emp_id",nullable = false,updatable = false)
    private Integer eId;
    @Column(name="fist_name")
    private String firstName;
    @Column(name="last_name")
    private String lastName;
    @ManyToMany(mappedBy = "employees")
    private List<Project> projects;
}

package com.oracle.repo;

import com.oracle.dto.Employee;
import org.springframework.data.jpa.repository.JpaRepository;

public interface EmployeeRepo extends JpaRepository<Employee,Integer> {
}

package com.oracle.repo;

import com.oracle.dto.Project;
import org.springframework.data.jpa.repository.JpaRepository;

public interface ProjectRepo extends JpaRepository<Project,Integer> {
}

package com.oracle.services;

import com.oracle.dto.Employee;
import com.oracle.dto.Project;
import com.oracle.repo.ProjectRepo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.transaction.Transactional;
import java.util.Date;
import java.util.LinkedList;
import java.util.List;

@Component
public class DBServices {
    @Autowired
    private ProjectRepo repo;
    @Transactional
    public void performActivity(){

        Project p1 = new Project();
        p1.setProjectName("Bank 2");
        p1.setTeamSize(20);
        p1.setStartDate(new Date(2020, 12, 22));

        Project p2 = new Project();
        p2.setProjectName("Bank 1");
        p2.setTeamSize(21);
        p2.setStartDate(new Date(2020, 12, 22));

        Project p3 = new Project();
        p3.setProjectName("Customs");
        p3.setTeamSize(11);
        p3.setStartDate(new Date(2010, 11, 20));

        Employee e1 = new Employee();
        e1.setFirstName("Pratik");
        e1.setLastName("Gaurav");

        Employee e2 = new Employee();
        e2.setFirstName("Ankita");
        e2.setLastName("Noopur");

        Employee e3 = new Employee();
        e3.setFirstName("Rudra");
        e3.setLastName("Narayan");

        List<Employee> empList1 = new LinkedList<Employee>();
        empList1.add(e2);
        empList1.add(e3);

        List<Employee> empList2 = new LinkedList<Employee>();
        empList2.add(e1);
        empList2.add(e2);

        List<Project> pl1=new LinkedList<Project>();
        pl1.add(p1);
        pl1.add(p2);

        List<Project> pl2=new LinkedList<Project>();
        pl2.add(p2);pl2.add(p3);

        p1.setEmployees(empList1);
        p2.setEmployees(empList2);

        e1.setProjects(pl1);
        e2.setProjects(pl2);

        repo.save(p1);
        repo.save(p2);
        repo.save(p3);

    }
}

在您的实体定义中，您没有为联接到事务的帐户指定@JoinColumn。你会想要这样的东西:

@Entity
public class Transaction {
    @ManyToOne(cascade = {CascadeType.ALL},fetch= FetchType.EAGER)
    @JoinColumn(name = "accountId", referencedColumnName = "id")
    private Account fromAccount;
}

编辑:嗯，我想如果您在类上使用@Table注释，那么这将是有用的。哈。：）

这是我的药。

Below is my Entity. Mark that the id is annotated with @GeneratedValue(strategy = GenerationType.AUTO), which means that the id would be generated by the Hibernate. Don't set it when entity object is created. As that will be auto generated by the Hibernate. Mind you if the entity id field is not marked with @GeneratedValue then not assigning the id a value manually is also a crime, which will be greeted with IdentifierGenerationException: ids for this class must be manually assigned before calling save()

@Entity
@Data
@NamedQuery(name = "SimpleObject.findAll", query="Select s FROM SimpleObject s")
public class SimpleObject {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @Column
    private String key;

    @Column
    private String value;

}

这是我的主类。

public class SimpleObjectMain {

    public static void main(String[] args) {

        System.out.println("Hello Hello From SimpleObjectMain");

        SimpleObject simpleObject = new SimpleObject();
        simpleObject.setId(420L); // Not right, when id is a generated value then no need to set this.
        simpleObject.setKey("Friend");
        simpleObject.setValue("Bani");

        EntityManager entityManager = EntityManagerUtil.getEntityManager();
        entityManager.getTransaction().begin();
        entityManager.persist(simpleObject);
        entityManager.getTransaction().commit();

        List<SimpleObject> simpleObjectList = entityManager.createNamedQuery("SimpleObject.findAll").getResultList();
        for(SimpleObject simple : simpleObjectList){
            System.out.println(simple);
        }

        entityManager.close();
        
    }
}

我想救它的时候，它把它扔出去了

PersistentObjectException: detached entity passed to persist.

我所需要修复的是删除主方法中simpleObject的id设置行。