idea中注解配置一对多,多对一,双向多对一映射(不详细)

一对多

package cn.pojo;

import javax.persistence.*;

import java.io.Serializable;

import java.util.Set;

@Entity //声明这是一个实体类 必写

public class District implements Serializable {

    private static final long serialVersionUID = 8009273978191878070L;

    //编号

    @Id //标识属性 相当于数据库中的主键

    @GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "seq_dis")   //strategy设置标识的生成策略

    @SequenceGenerator(name = "seq_dis",sequenceName = "seq_dis_id", //声明序列 自动增长唯1 从1开始自增

            allocationSize = ,initialValue = )

    private Integer id;

    //区县名称

    @Column(name = "name")  //将属性映射到数据库中 填写列名不区分大小写

    private String name;

    //街道

    @OneToMany(cascade = {CascadeType.ALL}) //一对多,不需要指定类型,cascade是为了指定级联操作。

    @JoinColumn(name = "district_Id")  //另一个表的外键 填写列名 有了@joincolumn注解 就不能有mappedBy属性否则会出兼容问题这个跟hibernate版本有关.我的是5

    private Set<Street> streetSet;

    public Set<Street> getStreetSet() {

        return streetSet;

    }

    public void setStreetSet(Set<Street> streetSet) {

        this.streetSet = streetSet;

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public District(Integer id, String name) {

        this.id = id;

        this.name = name;

    }

    public District(){}

}

多对一　　

package cn.pojo;

import javax.persistence.*;

import java.io.Serializable;

import java.util.Set;

@Entity //声明这是一个实体类 必写

public class Street implements Serializable {

    private static final long serialVersionUID = 2465299058773906791L;

    //编号

    @Id //标识属性

    @GeneratedValue(strategy = GenerationType.IDENTITY) //设置生成策略

    private Integer id;

    //街道名称

    @Column(name = "name")   //将属性映射到数据库中 填写列名 不区分大小写

    private String name;

    //所属区县

    @ManyToOne  //多对一

    @JoinColumn(name = "district_Id")   //指向另一个表的外键 填写列名

    private District district;

    @OneToMany

    @JoinColumn(name = "street_id")

    private Set<House> houses;

    public District getDistrict() {

        return district;

    }

    public void setDistrict(District district) {

        this.district = district;

    }

    public Integer getId() {

        return id;

    }

    public void setId(Integer id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Street(){}

}

多对多

package entity;

import javax.persistence.*;

import java.util.Objects;

import java.util.Set;

@Entity

public class EmployeeEntity {

    private long empid;

    //员工名

    private String empname;

    //开发过的项目

    private Set<ProjectEntity> projects;

    @ManyToMany(cascade=CascadeType.ALL,fetch=FetchType.LAZY)

    @JoinTable(name = "proemp"  //中间表的名字

            ,joinColumns ={@JoinColumn(name = "rempid")}    //与当前id有关的外键

            ,inverseJoinColumns = {@JoinColumn(name = "rproid")})   //另一个表有关的外键,也就是跟Project

    public Set<ProjectEntity> getProjects() {

        return projects;

    }

    public void setProjects(Set<ProjectEntity> projects) {

        this.projects = projects;

    }

    @Id

    public long getEmpid() {

        return empid;

    }

    public void setEmpid(long empid) {

        this.empid = empid;

    }

    @Column(name = "EMPNAME")

    public String getEmpname() {

        return empname;

    }

    public void setEmpname(String empname) {

        this.empname = empname;

    }

}

package entity;

import javax.persistence.*;

import java.util.Objects;

import java.util.Set;

@Entity

public class ProjectEntity {

    private long proid;

    //项目名称

    private String proname;

    //工作人员

    private Set<EmployeeEntity> employees;

    @ManyToMany

    @JoinTable(name = "proemp"  //如上

            ,joinColumns ={@JoinColumn(name = "rproid")} //如上

            ,inverseJoinColumns = {@JoinColumn(name = "rempid")}) //如上

    public Set<EmployeeEntity> getEmployees() {

        return employees;

    }

    public void setEmployees(Set<EmployeeEntity> employees) {

        this.employees = employees;

    }

    @Id

    @Column(name = "PROID")

    public long getProid() {

        return proid;

    }

    public void setProid(long proid) {

        this.proid = proid;

    }

    @Column(name = "PRONAME")

    public String getProname() {

        return proname;

    }

    public void setProname(String proname) {

        this.proname = proname;

    }

}

多对多测试的时候出现了一个问题如下

An AnnotationConfiguration instance is required to use <mapping class="entity.ProjectEntity"/>

　意思是，用了注解了，自然要用注解类生成SessionFactory,刚出现的时候很懵逼,因为说hibernate4以上的版本是不会出现这种问题的,于是找了半天.

最后发现就是这个问题如下

configuration=new AnnotationConfiguration();

//configuration = new Configuration().configure(); 注释这一段加上 上面一段 下面再多点下configure();

//获取session对象

sessionFactory =configuration.configure().buildSessionFactory();

因为自动生成的注解是在get上面的所以就没改了.