注解关联映射

最新推荐文章于 2025-08-22 13:45:39 发布

piperzero

最新推荐文章于 2025-08-22 13:45:39 发布

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文章标签： java 数据库

本文详细介绍了在ORM中一对多、多对一及双向关联的实现方式，并展示了如何通过@Column注解进行属性映射，以及如何执行本地化查询和HQL查询。

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一、一对多

@Id @GeneratedValue(generator = "emp", strategy = GenerationType.SEQUENCE) @SequenceGenerator(name="emp",sequenceName="emp_seq",allocationSize=1) private Integer empno; @ManyToOne(targetEntity=Dept.class) @JoinColumn(name = "deptno", updatable = false) @Basic(fetch = FetchType.LAZY) /* @Basic注解可以声明属性的获取策略(fetch strategy) */ private Dept dept; @Column(name = "ename") private String ename; @Column(name = "job") private String job; @Column(name = "mgr") private Short mgr; @Column(name = "hiredate") private Date hiredate; @Column(name = "sal") private Double sal; @Column(name = "comm") private Double comm; @Version @Column(name = "version") private Integer version;
@Id private Integer deptno; @Column(name="dname") private String dname; @Column(name="loc") private String loc;
三、多对一、一对多双向

@Id private Integer deptno; @Column(name="dname") private String dname; @Column(name="loc") private String loc; @OneToMany(cascade={CascadeType.ALL},targetEntity=Emp.class) @JoinColumn(name="deptno",updatable=false) private Set emps = new HashSet();
@Id @GeneratedValue(generator = "emp", strategy = GenerationType.SEQUENCE) @SequenceGenerator(name="emp",sequenceName="emp_seq",allocationSize=1) private Integer empno; @ManyToOne(targetEntity=Dept.class) @JoinColumn(name = "deptno", updatable = false) @Basic(fetch = FetchType.LAZY) /* @Basic注解可以声明属性的获取策略(fetch strategy) */ private Dept dept; @Column(name = "ename") private String ename; @Column(name = "job") private String job; @Column(name = "mgr") private Short mgr; @Column(name = "hiredate") private Date hiredate; @Column(name = "sal") private Double sal; @Column(name = "comm") private Double comm; @Version @Column(name = "version") private Integer version;

注：当属性名和数据库字段名不一致时，要显示指定@Column

使用 @Column 注解可将属性映射到列. 使用该注解来覆盖默认值(关于默认值请参考EJB3规范). 在属性级使用该注解的方式如下：

①不进行注解

②和 @Basic一起使用

③和 @Version一起使用

④和 @Lob一起使用

⑤和 @Temporal一起使用

⑥和 @org.hibernate.annotations.CollectionOfElements一起使用 (只针对Hibernate )

四、本地化查询

@NamedNativeQuery(name="dept&emp",query="select d.*,e.* from dept d,emp e where e.deptno=d.deptno",resultSetMapping="joinMapping") @SqlResultSetMapping(name="joinMapping",entities={ @EntityResult(entityClass=Dept.class), @EntityResult(entityClass=Emp.class) } )

List<Object[]> l=sess.getNamedQuery("dept&emp").list(); for (Object[] objects : l) { Dept d=(Dept)objects[0]; Emp e=(Emp)objects[1]; System.out.println(d.getDname()+" "+e.getEname()); }

五、HQL查询

@NamedQuery(name = "sqlquery", query = "select e from Emp e where e.dept.deptno = :dno")sess.getNamedQuery("sqlquery").setInteger("dno", 10).list().size()

注解 关联映射

注解关联映射