学好hibernate系列之常用注解开发

￡神魔★判官ぃ 2022-07-17 01:09 198阅读 0赞

1.hibernate到底有哪些常用注解？

（1）类级别注解

@Entity @Embeddable @Table

（2）属性级别

@Id @GeneratedValue @GenericGenerator

@Column @Emebedded @EmbeddedId

（3）映射关系注解

@ManyToOne @OneToMany @OneToOne(mappedBy="xx")

@ ManyToMany(mappedBy="xx")@JoinColumn @JoinTable

基本上开发常用的就是以上几个注解了，在这要注意以下导入jar包的时候，要导入那个JPA的jar包，需要用到hibernate的在导入hibernate框架的jar包，还有每个实体类或者引入的类，都必须要在hibernate.cfg.xml里面注入，即<mapping class="类的路径"/>

2.这些注解意味着什么，到底怎么用？什么时候用？

2.1   @Entity：很明显，这个是代表注册实体类的，就是我们建立的符合javaBean规范的实体类。

@Table：这个也很容易理解，这个是对应实体类在数据库表的声明，@Table(name="要生成的表名",schema="数据库"，catalog="目录(mysql不支持，所以一般去掉)")

！！！！@Entity跟@Table这两个实体类的注解一般是一起使用的

@Embeddable：这个注解也很好理解，这个是用来标明非实体类在实体类中的引用，常常跟@Embedded一起使用。

@Id：标明主键

@GeneratedValue：主键策略生成器,属性：（generator=”主键的名字（只常用这一个）“，strategy=GenerationType.AUTO（自动生成，一般不用到））

@@GenericGenerator ：主键生成策略，属性有（name="上面主键的名字",strategy="主键生成的策略assigned等"）

@Column(length=45)：数据库表字段的长度。

下面看看代码：

package com.hibernate.test01.dao.pojo002;
    
    import javax.persistence.Embedded;
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.Table;
    
    import org.hibernate.annotations.GenericGenerator;
    
    //注明实体类
    @Entity
    @Table(name="t_location",schema="mytest")
    public class Location {
    	@Id
    	@GeneratedValue(generator="provinceId")
    	@GenericGenerator(name="provinceId",strategy="assigned")
    	private String provinceId;
    	private String provinceName;
    	//注明要引用的类
    	@Embedded
    	private City city;
    	public Location() {
    		// TODO Auto-generated constructor stub
    	}
    	public Location(String provinceId, String provinceName, City city) {
    		super();
    		this.provinceId = provinceId;
    		this.provinceName = provinceName;
    		this.city = city;
    	}
    	public String getProvinceId() {
    		return provinceId;
    	}
    	public void setProvinceId(String provinceId) {
    		this.provinceId = provinceId;
    	}
    	public String getProvinceName() {
    		return provinceName;
    	}
    	public void setProvinceName(String provinceName) {
    		this.provinceName = provinceName;
    	}
    	public City getCity() {
    		return city;
    	}
    	public void setCity(City city) {
    		this.city = city;
    	}
    	
    
    }

package com.hibernate.test01.dao.pojo002;
    
    import javax.persistence.Embeddable;
    //注明是非实体类，被引入的类
    @Embeddable
    public class City {
    	private String cityId;
    	private String cityName;
    	public City() {
    		// TODO Auto-generated constructor stub
    	}
    	public City(String cityId, String cityName) {
    		super();
    		this.cityId = cityId;
    		this.cityName = cityName;
    	}
    	public String getCityId() {
    		return cityId;
    	}
    	public void setCityId(String cityId) {
    		this.cityId = cityId;
    	}
    	public String getCityName() {
    		return cityName;
    	}
    	public void setCityName(String cityName) {
    		this.cityName = cityName;
    	}
    	
    }

测试类：

package com.hibernate.test01.dao.pojo002;
    
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import org.junit.Test;
    
    import com.hibernate.test01.HibernateSessionFactory;
    
    public class test002 {
    
    	@Test
    	public void test() {
    		Session session = HibernateSessionFactory.getSessionFactory().getCurrentSession();
    		City c = new City("c001","New York");
    		Location l = new Location("p001","jffsf",c);
    		Transaction tx = session.beginTransaction();
    		session.save(l);
    		tx.commit();
    	}
    
    }

@EmbeddedId：用来标明联合主键的，跟@Embeddable一起使用，用代码来看看：

package com.hibernate.test01.dao.pojo002;
    
    import javax.persistence.Column;
    import javax.persistence.Embeddable;
    
    @Embeddable
    public class Student_PK {
    	@Column(length=50)
    	private String studentId;
    	@Column(length=50)
    	private String CourseId;
    	public Student_PK() {
    		// TODO Auto-generated constructor stub
    	}
    	public Student_PK(String studentId, String courseId) {
    		super();
    		this.studentId = studentId;
    		CourseId = courseId;
    	}
    	public String getStudentId() {
    		return studentId;
    	}
    	public void setStudentId(String studentId) {
    		this.studentId = studentId;
    	}
    	public String getCourseId() {
    		return CourseId;
    	}
    	public void setCourseId(String courseId) {
    		CourseId = courseId;
    	}
    	
    
    }

package com.hibernate.test01.dao.pojo002;
    
    import javax.persistence.EmbeddedId;
    import javax.persistence.Entity;
    import javax.persistence.Table;
    
    @Entity
    @Table(name="student001")
    public class Student01 {
    	@EmbeddedId
    	private Student_PK pk;
    	private String stuName;
    	private String address;
    	public Student01() {
    		// TODO Auto-generated constructor stub
    	}
    	public Student01(Student_PK pk, String stuName, String address) {
    		super();
    		this.pk = pk;
    		this.stuName = stuName;
    		this.address = address;
    	}
    	public Student_PK getPk() {
    		return pk;
    	}
    	public void setPk(Student_PK pk) {
    		this.pk = pk;
    	}
    	public String getStuName() {
    		return stuName;
    	}
    	public void setStuName(String stuName) {
    		this.stuName = stuName;
    	}
    	public String getAddress() {
    		return address;
    	}
    	public void setAddress(String address) {
    		this.address = address;
    	}
    	 
    }

3.映射关系注解

@ManyToOne：表示实体跟实体之间存在多对一的关系，使用的时候在主类，实例化要引入的实体类，或者在getter方法前面引入（多对一单向外键）

@OneToMany：表示实体跟实体之间存在一对多的关系，使用的使用在一的一方用Set<多的一方的实体类对象>标签（一对多单向外键）

@OneToOne(mappedBy="xx")表示实体跟实体之间存在一对多的关系

@ ManyToMany(mappedBy="xx哪个类来维护相互的关系")@JoinTable\{JoinColumn=\{@JoinColumn="主键的名",inserveJoinColumn=\{@JoinColumn="外键的名"\}\}\}

在双方的实体类中都用上，并且用Set<多的一方的实体类对象>标签。

@JoinColumn (name="外键名")：用来声明外键，就是谁作为外键之间的关系。

下面是代码：

package com.hibernate.test01.dao.pojo01;
    
    import javax.persistence.CascadeType;
    import javax.persistence.Embedded;
    import javax.persistence.Entity;
    import javax.persistence.FetchType;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.ManyToOne;
    
    import org.hibernate.annotations.GenericGenerator;
    
    @Entity
    public class student {
    	@Id
    	@GeneratedValue(generator="sid")
    	@GenericGenerator(name="sid",strategy="assigned")
    	private String sid;
    	private String sname;
    	@Embedded
    	private Address addr;
    	@ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
    	@JoinColumn(name="ClassId")
    	private ClassRoom classRoom;
    	@ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
    	@JoinColumn(name="Uid")
    	private IDCard idcard;
    	public student() {
    		// TODO Auto-generated constructor stub
    	}
    	public student(String sid, String sname, Address addr, IDCard idcard) {
    		super();
    		this.sid = sid;
    		this.sname = sname;
    		this.addr = addr;
    		this.idcard = idcard;
    	}
    	public String getSid() {
    		return sid;
    	}
    	public void setSid(String sid) {
    		this.sid = sid;
    	}
    	public String getSname() {
    		return sname;
    	}
    	public void setSname(String sname) {
    		this.sname = sname;
    	}
    	public Address getAddr() {
    		return addr;
    	}
    	public void setAddr(Address addr) {
    		this.addr = addr;
    	}
    	public IDCard getIdcard() {
    		return idcard;
    	}
    	public void setIdcard(IDCard idcard) {
    		this.idcard = idcard;
    	}
    	
    }

package com.hibernate.test01.dao.pojo01;
    
    import java.util.Set;
    
    import javax.persistence.CascadeType;
    import javax.persistence.Entity;
    import javax.persistence.FetchType;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    import javax.persistence.JoinColumn;
    import javax.persistence.OneToMany;
    
    import org.hibernate.annotations.GenericGenerator;
    @Entity
    public class ClassRoom {
    	@Id
    	@GeneratedValue(generator="ClassId")
    	@GenericGenerator(name="ClassId",strategy="assigned")
    	private String ClassId;
    	private String className;
    	@OneToMany(cascade={CascadeType.ALL},fetch=FetchType.LAZY)
    	@JoinColumn(name="ClassId")
    	private Set<student> students;
    	public ClassRoom() {
    		// TODO Auto-generated constructor stub
    	}
    	public ClassRoom(String classId, String className, Set<student> students) {
    		super();
    		ClassId = classId;
    		this.className = className;
    		this.students = students;
    	}
    	public String getClassId() {
    		return ClassId;
    	}
    	public void setClassId(String classId) {
    		ClassId = classId;
    	}
    	public String getClassName() {
    		return className;
    	}
    	public void setClassName(String className) {
    		this.className = className;
    	}
    	public Set<student> getStudents() {
    		return students;
    	}
    	public void setStudents(Set<student> students) {
    		this.students = students;
    	}
    
    
    }

package com.hibernate.test01.dao.pojo01;
    
    import javax.persistence.Embeddable;
    
    
    @Embeddable
    public class Address {
    	
    	private String aid;
    	private String provice;
    	private String city;
    	public Address() {
    		// TODO Auto-generated constructor stub
    	}
    	public String getAid() {
    		return aid;
    	}
    	public void setAid(String aid) {
    		this.aid = aid;
    	}
    	public String getProvice() {
    		return provice;
    	}
    	public void setProvice(String provice) {
    		this.provice = provice;
    	}
    	public String getCity() {
    		return city;
    	}
    	public void setCity(String city) {
    		this.city = city;
    	}
    	public Address(String aid, String provice, String city) {
    		super();
    		this.aid = aid;
    		this.provice = provice;
    		this.city = city;
    	}
    
    }

package com.hibernate.test01.dao.pojo01;
    
    import javax.persistence.Entity;
    import javax.persistence.GeneratedValue;
    import javax.persistence.Id;
    
    import org.hibernate.annotations.GenericGenerator;
    
    @Entity
    public class IDCard {
    	@Id
    	@GeneratedValue(generator="Uid")
    	@GenericGenerator(name="Uid",strategy="assigned")
    	private String Uid;
    	private String name;
    	public IDCard() {
    		// TODO Auto-generated constructor stub
    	}
    	
    	public IDCard(String uid, String name) {
    		super();
    		Uid = uid;
    		this.name = name;
    	}
    
    	public String getUid() {
    		return Uid;
    	}
    	public void setUid(String uid) {
    		Uid = uid;
    	}
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	
    }

package com.hibernate.test01.dao.pojo01;
    
    import java.util.HashSet;
    import java.util.Set;
    
    import org.hibernate.Session;
    import org.hibernate.Transaction;
    import org.junit.Test;
    
    import com.hibernate.test01.HibernateSessionFactory;
    
    public class test {
    
    	@Test
    	public void test() {
    		Session session = HibernateSessionFactory.getSessionFactory().getCurrentSession();
    		Transaction tx = session.beginTransaction();
    		IDCard id = new IDCard("464564","hfkdfhk");
    		Address a = new Address("add134","dfd","zq");
    		student s2 = new student("s0004","h555o",a,id);
    		student s1 = new student("s0003","545f",a,id);
    		Set<student> stu = new HashSet<student>();
    		stu.add(s1);
    		stu.add(s2);
    		ClassRoom c = new ClassRoom("c004","5f",stu);
    		session.save(id);
    		session.save(s1);
    		session.save(s2);
    		session.save(c);
    		tx.commit();
    	}
    
    }