java - hibernate:OneToMany RelationShip:实体表不接受多个值

Question

任何人都可以帮助我在我的 hibernate 程序中尝试实现 OneToMany 实体关系。我成功解决了第一步中的许多错误/异常，现在陷入了这个 Mysql 异常，并自 2 天以来一直在尝试解决

我只是想做这样的事情

我一步步提到我所做的事情

* 表创建

  create table area(acode varchar(100) not null, aname varchar(50) default null, primary key(acode));

   create table employee (acode varchar(100) not null,ecode varchar(50) not null, primary key(ecode), name varchar(50) default null,  key employee_foregin(acode),  constraint employee_foregin foreign key(acode) references area(acode));

• 添加 Maven 依赖项*

<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>
    <groupId>com.mishra.practice</groupId>
    <artifactId>HibernateDemo_1</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-core</artifactId>
            <version>5.4.15.Final</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.19</version>
        </dependency>

    </dependencies>
</project> 

<小时/>

• 区域实体*

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Area {
    @Id
    private String aCode;
    private String aName;
    @ManyToOne
    private Employee employee;

    public Employee getEmployee() {
        return employee;
    }
    public void setEmployee(Employee employee) {
        this.employee = employee;
    }
    public String getaCode() {
        return aCode;
    }
    public void setaCode(String aCode) {
        this.aCode = aCode;
    }
    public String getaName() {
        return aName;
    }
    public void setaName(String aName) {
        this.aName = aName;
    }

    public Area() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Area(String aCode, String aName) {
        super();
        this.aCode = aCode;
        this.aName = aName;
    }

    public Area(String aCode) {
        super();
        this.aCode = aCode;
    }


    @Override
    public String toString() {
        return "Area [aCode=" + aCode + ", aName=" + aName  + "]";
    }


}

• 员工实体*

import java.util.Collection;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Employee {
    @Id
    private String eCode;
    private String eName;

    @OneToMany(mappedBy = "employee")
    private Collection<Area> areas;

    public Collection<Area> getAreas() {
        return areas;
    }

    public void setAreas(Collection<Area> areas) {
        this.areas = areas;
    }

    public String geteCode() {
        return eCode;
    }

    public void seteCode(String eCode) {
        this.eCode = eCode;
    }

    public String geteName() {
        return eName;
    }

    public void seteName(String eName) {
        this.eName = eName;
    }

    public Employee() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Employee(String eCode, String eName, Collection<Area> areas) {
        super();
        this.eCode = eCode;
        this.eName = eName;
        this.areas = areas;

    }

    public Employee(String eCode, String eName) {
        super();
        this.eCode = eCode;
        this.eName = eName;
    }

    @Override
    public String toString() {
        return "Employee [eCode=" + eCode + ", eName=" + eName + "]";
    }

}

• 进入区域

package relationMapping.one_2_Many;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class AreaEntry {
    public static void main(String[] args) {
        Configuration configuration=new Configuration().configure();
        SessionFactory sessionFactory=configuration.buildSessionFactory();
        Session session= sessionFactory.openSession();
        Transaction transaction= session.beginTransaction();

        session.save(new Area("A111", "Indore_North"));
        session.save(new Area("A112", "Indore_South"));
        session.save(new Area("A113", "Indore_East"));
        session.save(new Area("A114", "Bhopal_south"));
        session.save(new Area("A115", "Bhopal_central"));

        transaction.commit();
        System.out.println("\n----------------All done-------------------");
        session.close();
    }
}

• 员工条目

package relationMapping.one_2_Many;

import java.util.ArrayList;
import java.util.List;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class EmployeeEntry {
    public static void main(String[] args) {
        Configuration configuration=new Configuration().configure();
        SessionFactory sessionFactory=configuration.buildSessionFactory();
        Session session= sessionFactory.openSession();
        Transaction transaction= session.beginTransaction();

        List<Area> list1=new ArrayList<Area>();
        list1.add(new Area("A101"));
        list1.add(new Area("A102"));
        session.persist(new Employee("E101", "Narendra",list1));



        List<Area> list2=new ArrayList<Area>();
        list2.add(new Area("A103"));
        list2.add(new Area("A104"));
        session.persist(new Employee("E102", "Nik", list2));

        List<Area> list3=new ArrayList<Area>();
        list3.add(new Area("A105"));
        list3.add(new Area("A104"));
        session.persist(new Employee("E103","Pradeep",list3));

        List<Area> list4=new ArrayList<Area>();
        list4.add(new Area("A104"));
        list4.add(new Area("A105"));
        session.persist(new Employee("E104", "Chetan", list4));

        List<Area> list5=new ArrayList<Area>();
        list5.add(new Area("A105"));
        list5.add(new Area("A101"));
        session.persist(new Employee("E105", "Dev", list5));

        transaction.commit();
        System.out.println("\n----------------All done-------------------");
        session.close();
    }
}

Answer 1

问题在于，在 Employee 表的 DDL 中，您定义了一个列 acode

   create table employee (acode varchar(100) not null,ecode varchar(50) not null, primary key(ecode), name varchar(50) default null,  key employee_foregin(acode),  constraint employee_foregin foreign key(acode) references area(acode));

此列未映射到您的 Employee Entity 类中的任何内容(但是您有一个名为 ecode 的列)

@Entity
public class Employee {
    @Id
    private String eCode;

这基本上就是错误消息告诉您的内容(未知列)

所以将Employee实体类中的ecode改为acode。顺便说一句，您应该让 Spring 为您生成数据库表以避免此类问题。