idea中注解配置一对多,多对一,双向多对一映射(不详细)

Posted 2021-01-22 hfx123

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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 = 1,initialValue = 1)
    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.