Hibernate基础知识（7）_private set<order> orders=new hashset<order>;-优快云博客

本文链接：https://blog.youkuaiyun.com/lsq_java_4/article/details/52300982

一、Hibernate注解应用

1、使用注解配置 PO对象
  @Entity 实体类
  @Table 生成目标表
  @Id 主键
  @GeneratedValue 主键生成策略
  @Column 定义生成列

☆：注解开发优先使用 javax.persistence.* 包

package lsq.hibernate.domain;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

//实体类
@Entity
// 设置生成表明
@Table(name = "book")
public class Book {
	// 主键
	@Id
	// 主键生成策略
	@GeneratedValue(strategy = GenerationType.IDENTITY)
	private Integer id;
	// 普通属性可以使用@Column注解修饰，如果不写，列名就是属性名
	@Column(name = "bookname", length = 20, unique = true, nullable = true)
	private String name;
	private Double price;

	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 Double getPrice() {
		return price;
	}

	public void setPrice(Double price) {
		this.price = price;
	}

}

* @Id、@GeneratedValue、@Column 可以修改属性，也可以放到属性get方法上

* 在hibernate.cfg.xml 配置注解类<mapping class="lsq.hibernate.domain.Book"/>

2、主键生成策略

@GeneratedValue(strategy = GenerationType.IDENTITY) --- 只支持四种策略
编写UUID 主键生成策略 Person

package lsq.hibernate.domain;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name="person")
public class Person {
	@Id
	@GenericGenerator(name="myuuidgenerator",strategy="uuid")
	@GeneratedValue(generator="myuuidgenerator")
	private String id;//UUID
	private String name;
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
}

3、其他属性

@Temporal 生成日期类型
@Transient 控制不生成


  日期类型java.util.Date 对于MySQL 生成 datetime类，日期和时间都包括
  * @Temporal(TemporalType.DATE) 数据表只保存日期
  * @Temporal(TemporalType.TIME) 数据表只保存时间
  * @Temporal(TemporalType.TIMESTAMP) 日期时间都保存

Hibernate 实体类中，所有get方法属性，都会在数据表自动生成列
* 有时属性不想生成列 @Transient 注解

4、一对多

配置Customer类：

package lsq.hibernate.domain;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;

import org.hibernate.annotations.Cascade;
import org.hibernate.annotations.CascadeType;
@Entity
@Table(name="customers")
public class Customer {
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Integer id;
	private String name;
	
	//targetEntity，类似<one-to-many class="">
	//mappedBy,作用类似inverse=true
	@OneToMany(targetEntity = Order.class, mappedBy = "customer")
	//配置级联
	@Cascade(value={CascadeType.SAVE_UPDATE})
	private Set<Order> orders = new HashSet<Order>();
	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 Set<Order> getOrders() {
		return orders;
	}
	public void setOrders(Set<Order> orders) {
		this.orders = orders;
	}
	
}

配置Orders

package lsq.hibernate.domain;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

@Entity
@Table(name = "orders")
public class Order {
	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Integer id;
	private String address;
	
	@ManyToOne(targetEntity=Customer.class)
	//添加外键列
	@JoinColumn(name="customer_id")
	private Customer customer;

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getAddress() {
		return address;
	}

	public void setAddress(String address) {
		this.address = address;
	}

	public Customer getCustomer() {
		return customer;
	}

	public void setCustomer(Customer customer) {
		this.customer = customer;
	}

}

☆：jar冲突错误 java.lang.NoSuchMethodError: javax.persistence.OneToMany.orphanRemoval()
* javaee.jar(myeclipse提供) 和 jpa的jar 冲突
* 解决：删除javaee.jar 中 javax.persistence 包

* 级联操作 @Cascade(value = { CascadeType.级别 })
DELETE_ORPHAN 已经过时，推荐使用 @OneToMany(orphanRemoval=true)
所有级联级别
@OneToMany(targetEntity = Order.class, mappedBy = "customer", orphanRemoval = true)
@Cascade(value = { CascadeType.ALL })
private Set<Order> orders = new HashSet<Order>();

5、多对多配置

@ManyToMany
* 注解配置多对多时，只需要一端配置中间表，另一端 mappedBy 放弃外键维护权

配置Course类：

package lsq.hibernate.domain;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Entity
@Table(name="courses")
public class Course {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private Integer id;
	private String cname;
	
	@ManyToMany(targetEntity = Student.class,mappedBy="courses")//把外键维护权交给对方
	private Set<Student> students = new HashSet<Student>();

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getCname() {
		return cname;
	}

	public void setCname(String cname) {
		this.cname = cname;
	}

	public Set<Student> getStudents() {
		return students;
	}

	public void setStudents(Set<Student> students) {
		this.students = students;
	}

}

配置Student类：

package lsq.hibernate.domain;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
@Entity
@Table(name="students")
public class Student {
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private Integer id;
	private String sname;
	
	@ManyToMany(targetEntity=Course.class)
	//配置中间表
	//joinColumns当前类在中间表中外键列名
	//inverseJoinColumns对方类在中间表中外键列名
	@JoinTable(name="student_course",joinColumns = {@JoinColumn(name="student_id")},inverseJoinColumns={@JoinColumn(name="course_id")})
	private Set<Course> courses = new HashSet<Course>();

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getSname() {
		return sname;
	}

	public void setSname(String sname) {
		this.sname = sname;
	}

	public Set<Course> getCourses() {
		return courses;
	}

	public void setCourses(Set<Course> courses) {
		this.courses = courses;
	}

}

6、抓取策略（了解）
public class Customer {
// 抓取策略
@Fetch(FetchMode.SELECT)
@LazyCollection(LazyCollectionOption.TRUE)
private Set<Order> orders = new HashSet<Order>();
}

public class Order {
// 抓取策略
@Fetch(FetchMode.SELECT)
@LazyToOne(LazyToOneOption.FALSE)
private Customer customer;
}

关联级别抓取，配置@Fetch等价fetch属性，关联集合 @LazyCollection ，关联单一对象 @LazyToOne

7、 NamedQuery 命名查询
@NamedQueries(value = { @NamedQuery(name = "findCustomerByName", query = "from Customer where name= ?") })
public class Customer {
...
}

程序代码：
Query query = session.getNamedQuery("findCustomerByName");
query.setParameter(0, "张三");
Customer customer = (Customer) query.uniqueResult();