Java 如何设置JPA中表之间的关系？

我得到了一个错误：

字段列表中的未知列“employee0\u 2\u.employee\u id”

我的领域有什么问题？少了什么

完整堆栈跟踪：

Exception in thread "main" javax.persistence.PersistenceException: org.hibernate.exception.SQLGrammarException: could not extract ResultSet
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1387)
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1310)
at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1316)
at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:898)
at tests.ApplTest.main(ApplTest.java:38)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
Caused by: org.hibernate.exception.SQLGrammarException: could not extract ResultSet
at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:82)
at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:61)
at org.hibernate.loader.Loader.getResultSet(Loader.java:2040)
at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1837)
at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:1816)
at org.hibernate.loader.Loader.doQuery(Loader.java:900)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:342)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:312)
at org.hibernate.loader.Loader.loadEntity(Loader.java:2121)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:82)
at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:72)
at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3927)
at org.hibernate.event.internal.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:460)
at org.hibernate.event.internal.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:429)
at org.hibernate.event.internal.DefaultLoadEventListener.load(DefaultLoadEventListener.java:206)
at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:262)
at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:150)
at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1092)
at org.hibernate.internal.SessionImpl.access$2000(SessionImpl.java:175)
at org.hibernate.internal.SessionImpl$IdentifierLoadAccessImpl.load(SessionImpl.java:2476)
at org.hibernate.internal.SessionImpl.get(SessionImpl.java:992)
at org.hibernate.event.internal.DefaultMergeEventListener.entityIsDetached(DefaultMergeEventListener.java:271)
at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:151)
at org.hibernate.event.internal.DefaultMergeEventListener.onMerge(DefaultMergeEventListener.java:76)
at org.hibernate.internal.SessionImpl.fireMerge(SessionImpl.java:914)
at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:898)
at org.hibernate.internal.SessionImpl.merge(SessionImpl.java:902)
at org.hibernate.ejb.AbstractEntityManagerImpl.merge(AbstractEntityManagerImpl.java:889)
... 6 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'employee0_2_.employee_id' in 'field list'
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.Util.getInstance(Util.java:381)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1030)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3491)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3423)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1936)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2060)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2542)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1734)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1885)
at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:56)

MySql表：

CREATE TABLE Employee(employee_id INTEGER PRIMARY KEY NULL , name VARCHAR(50) UNIQUE NULL , salary VARCHAR(50) null , specialization VARCHAR(50) NULL);
CREATE TABLE Managers(name  VARCHAR(50) NULL UNIQUE , lastname VARCHAR(50) NULL UNIQUE , manager_id INTEGER NULL PRIMARY KEY AUTO_INCREMENT, FOREIGN KEY (manager_id) REFERENCES Employee(employee_id) );
CREATE TABLE Department (department_id INTEGER PRIMARY KEY AUTO_INCREMENT ,name VARCHAR(50) UNIQUE NULL , FOREIGN KEY (department_id) REFERENCES Managers(manager_id));

雇员：

@Entity
@Table (name = "employee")
@Inheritance(strategy = InheritanceType.JOINED)
public class Employee{

public Employee(int id, String name, double salary, String specialization) {
    this.employee_id = id;
    this.name = name;
    this.salary = salary;
    this.specialization = specialization;
}

@Override
public String toString() {
    return "Employee{" +
            "id=" + employee_id +
            ", name='" + name + '\'' +
            ", salary=" + salary +
            ", deg='" + specialization + '\'' +
            '}';
}

public int getId() {
    return employee_id;
}

public void setId(int id) {
    this.employee_id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public double getSalary() {
    return salary;
}

public void setSalary(double salary) {
    this.salary = salary;
}

public String getSpecialization() {
    return specialization;
}

public void setSpecialization(String specialization) {
    this.specialization = specialization;
}

@Id
@Column(name = "employee_id")
private int employee_id;

@Column(name = "name")
private String name;
@Column(name = "salary")
private double salary;
@Column (name = "specialization")
private String specialization;

public Employee(){}
}

部门：

@Table(name = "department")
@Entity
@Inheritance(strategy = InheritanceType.JOINED)
public class Department extends Managers{

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public Department(String name) {
    this.name = name;
}

public Managers getManager() {
    return manager;
}

public void setManager(Managers manager) {
    this.manager = manager;
}

@OneToOne
@JoinColumn(name = "department_id" , referencedColumnName = "manager_id", insertable = false, updatable = false)
private Managers manager;

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

public int getDepartment_id() {
    return department_id;
}

public void setDepartment_id(int department_id) {
    this.department_id = department_id;
}

@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "department_id")
private int department_id;

public Department(){}

}

经理：

@Table(name = "managers")
@Entity
public class Managers extends Employee{

@OneToOne
@JoinColumn(name = "manager_id", referencedColumnName = "employee_id" , insertable = false, updatable = false)
private Employee employee;

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getLastname() {
    return lastname;
}

public void setLastname(String lastname) {
    this.lastname = lastname;
}

public Managers(String name, String lastname) {
    this.name = name;
    this.lastname = lastname;
}

public Managers(){}

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

public int getManager_id() {
    return manager_id;
}

public void setManager_id(int manager_id) {
    this.manager_id = manager_id;
}

@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "manager_id")
private int manager_id;

}

Persistence.xml：

   <?xml version="1.0" encoding="UTF-8"?>
   <persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
   http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">

<persistence-unit name="EmployeesTesting" transaction-type="RESOURCE_LOCAL">

    <provider>org.hibernate.ejb.HibernatePersistence</provider>

    <class>employee.Employee</class>
    <class>department.Department</class>
    <class>managers.Managers</class>

    <properties>
        <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/employees"/>
        <property name="javax.persistence.jdbc.user" value="root"/>
        <property name="javax.persistence.jdbc.password" value="****"/>
        <property name="javax.persistence.jdbc.Driver" value="com.mysql.jdbc.Driver"/>
    </properties>

</persistence-unit>

---

已更新

我已经根据您的配置做了一些测试，这是您需要做的，以便实现：

第一步

• 从实体定义中删除

  @继承（strategy=InheritanceType.JOINED）

  注释
• 从

  经理

  和

  部门

第二步

@OneToOne

映射应如下所示

雇员：

@Entity
public class Employee {

    @Id
    @Column(name = "employee_id")
    private Integer employeeId;

    @OneToOne(mappedBy = "employee")
    private Manager manager;

经理：

@Entity

public class Manager {

    @Id
    @Column(name = "manager_id")
    private Integer managerId;

    @MapsId
    @OneToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "manager_id", referencedColumnName = "employee_id")
    private Employee employee;

部门：

@Entity
public class Department {

    @Id
    @Column(name = "department_id")
    private Integer departmentId;

    @MapsId
    @OneToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "department_id", referencedColumnName = "manager_id")
    private Manager manager;

别忘了接球手和二传手

第三步

为了正确保存所有实体，使它们都有一个共享id，您只需保存

部门

。。看起来是这样的：

        Employee emp = new Employee();
        emp.setEmployeeId(1);
        emp.setName("employee");

        Manager manager = new Manager();
        manager.setEmployee(emp);
        manager.setName("manager");

        Department department = new Department();
        department.setName("department");
        department.setManager(manager);

        em.persist(department);

---

提交交易后，所有三个实体的主键都将设置为

1

我的问题的答案是：

1.将属性添加到persistence.xml！为了允许提供者创建表

<property name="hibernate.hbm2ddl.auto" value="create"/>

---

我认为这个部门不太可能从一开始就延长经理的任期。经理是雇员。经理/员工有一个部门。我删除了继承扩展策略并添加了@Id！现在我遇到了这个错误：无法添加或更新子行：外键约束失败（

employees

managers

，约束

managers\u ibfk\u 1

外键（

manager\u id

）引用

employeer

（

employeer\u id

）我将从@JoinColumn注释中删除那些“insertable=false”属性。您肯定要插入这些。。可能不更新，但插入YetOK，但我得到相同的异常！也有同样的例外！我删除了@继承策略！我对子行的约束也有同样的问题！！你确定你理解这个例外吗？

<property name="hibernate.hbm2ddl.auto" value="create"/>

@Entity
@Table (name = "employee")
public class Employee {

public Employee(int id, String name, String lastname, double salary, String spec) {
    this.id = id;
    this.name = name;
    this.salary = salary;
    this.specialization = spec;
    this.lastname = lastname;
}

public int getId() {
    return id;
}

public String getName() {
    return name;
}

public double getSalary() {
    return salary;
}

public void setId(int id) {
    this.id = id;
}

public void setName(String name) {
    this.name = name;
}

public void setSalary(double salary) {
    this.salary = salary;
}

@Override
public String toString() {
    return "Employee{" +
            "id=" + id +
            ", name='" + name + '\'' +
            ", salary=" + salary +
            ", deg='" + specialization + '\'' +
            '}';
}

public String getLastname() {
    return lastname;
}

public void setLastname(String lastname) {
    this.lastname = lastname;
}

@Id
@Column(name = "id")
private int id;

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

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

@Column(name = "salary")
private double salary;

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

public Managers getManagers() {
    return manager;
}

public void setManagers(Managers manager) {
    this.manager = manager;
}

@OneToOne(cascade = {CascadeType.ALL})
@JoinColumn(name = "manager_id")
private Managers manager;

public Employee(){}
}