从一关联到多的查询和从多关联到一的查询来简单说说关联查询。
实体Team:球队。
实体Player:球员。
球队和球员是一对多的关系。
Team.java:
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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; /** * 球队 * @author Luxh */ @Entity @Table (name= "team" ) public class Team{ @Id @GeneratedValue private Long id; /**球队名称*/ @Column (name= "name" ,length= 32 ) private String name; /**拥有的球员*/ @OneToMany (mappedBy= "team" ,cascade=CascadeType.ALL,fetch=FetchType.LAZY) private Set<Player> players = new HashSet<Player>(); |