從一關(guān)聯(lián)到多的查詢和從多關(guān)聯(lián)到一的查詢來(lái)簡(jiǎn)單說(shuō)說(shuō)關(guān)聯(lián)查詢。
實(shí)體Team：球隊(duì)。
實(shí)體Player：球員。
球隊(duì)和球員是一對(duì)多的關(guān)系。
Team.java:
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
|
package com.cndatacom.jpa.entity;import java.util.HashSet;import java.util.Set;import javax.persistence.CascadeType;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.FetchType;import javax.persistence.GeneratedValue;import javax.persistence.Id;import javax.persistence.OneToMany;import javax.persistence.Table;/** * 球隊(duì) * @author Luxh */@Entity@Table(name="team")public class Team{ @Id @GeneratedValue private Long id; /**球隊(duì)名稱*/ @Column(name="name",length=32) private String name; /**擁有的球員*/ @OneToMany(mappedBy="team",cascade=CascadeType.ALL,fetch=FetchType.LAZY) private Set<Player> players = new HashSet<Player>(); |