Hibernate关系映射总结

最新推荐文章于 2024-08-05 14:34:00 发布

最新推荐文章于 2024-08-05 14:34:00 发布 · 105 阅读

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本文详细介绍了Java中常见的对象关系映射(ORM)技术，包括一对一、一对多、多对多等不同类型的关联映射方式，并提供了具体的注解使用示例。

其实这些东东完全可以参考帮助文档；这里只是总结下。
》》》一对一映射
妻子类

	@OneToOne
	@JoinColumn(name="husbandID")
	public Husband getHusband() {
		return husband;
	}

丈夫类

	@OneToOne(cascade=CascadeType.ALL,mappedBy="husband")
	public Wife getWife() {
		return wife;
	}

》》》一对多映射
班级类

	@OneToMany(mappedBy="class1",fetch=FetchType.LAZY)
	public Set<Student> getStudents() {
		return students;
	}

学生类

	@ManyToOne(fetch=FetchType.EAGER)
	@JoinColumn(name="classID")
	public Class1 getClass1() {
		return class1;
	}

》》》多对多映射

用户类

	@ManyToMany(targetEntity=com.xj.model.Role.class,
			cascade=CascadeType.PERSIST)
	@JoinTable(name="t_user_role",
			joinColumns=@JoinColumn(name="userID"),
			inverseJoinColumns=@JoinColumn(name="roleID"))
	public Set<Role> getRoles() {
		return roles;
	}

角色类

	@ManyToMany(targetEntity=com.xj.model.User.class,
			mappedBy="roles")
	public Set<User> getUsers() {
		return users;
	}

》》》联合主键映射
有三种方式这里只是其中一种。

主键类（实现Serializable接口，重写hashCode、equals方法）

public class NamePK implements Serializable{
	private String firstName;
	private String lastName;
	public String getFirstName() {
		return firstName;
	}
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
	public String getLastName() {
		return lastName;
	}
	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result
				+ ((firstName == null) ? 0 : firstName.hashCode());
		result = prime * result
				+ ((lastName == null) ? 0 : lastName.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		final NamePK other = (NamePK) obj;
		if (firstName == null) {
			if (other.firstName != null)
				return false;
		} else if (!firstName.equals(other.firstName))
			return false;
		if (lastName == null) {
			if (other.lastName != null)
				return false;
		} else if (!lastName.equals(other.lastName))
			return false;
		return true;
	}
}

用到主键类的学生类

@IdClass(NamePK.class)
@Entity
@Table(name="t_student")
public class Student {
......
	@Id
	public String getFirstName() {
		return firstName;
	}
	@Id
	public String getLastName() {
		return lastName;
	}
}

》》》组件映射
组件类

@Embeddable
public class NamePK implements Serializable{

用到组件类的类

private NamePK namePK;

》》》外键映射
学生类

	@ManyToOne(fetch=FetchType.EAGER)
	@JoinColumn(name="classID")
	public Class1 getClass1() {
		return class1;
	}

》》》继承映射

若把父类@MappedSuperclass换成@Entity则只生成一张表且包含所有子类信息！！

父类Cat类

@MappedSuperclass
public class Cat {}

子类1

@Entity
@Table(name="t_beijingcat")
public class BeijingCat extends Cat {

子类2

@Entity
@Table(name="t_shanghaiCat")
public class BeijingCat extends Cat {