hibernate3的注解映射学习-优快云博客

本文链接：https://blog.youkuaiyun.com/astro_boy/article/details/83485030

本文详细介绍了Hibernate中各类注解的应用，包括实体类、属性、表映射等，并深入探讨了一对一、一对多、多对一及多对多等各种表间关系的映射方式。

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注解映射必须满足两大条件：Hibernate3.2以上版本和JSEE 5。
@Entity 类注释，所有要持久化的类都要有

Java代码

@Entity
public class Org implements java.io.Serializable {
}

@Entity
public class Org  implements java.io.Serializable {
}

@Id 主键

Java代码

@Id
@GeneratedValue
private String orgId;
private String orgName;

@Id
     @GeneratedValue
     private String orgId;
     private String orgName;

@Column(name="...") 该属性对应表中的字段是什么，没有name表示一样
@Table 对象与表映射
@UniqueConstraint 唯一约束
@Version 方法和字段级，乐观锁用法，返回数字和timestamp，数字为首选
@Transient 暂态属性，表示不需要处理
@Basic 最基本的注释。有两个属性：fetch是否延迟加载，optional是否允许null
@Enumerated 枚举类型
@Temporal 日期转换。默认转换Timestamp
@Lob 通常与@Basic同时使用，提高访问速度。
@Embeddable 类级，表可嵌入的
@Embedded 方法字段级，表被嵌入的对象和@Embeddable一起使用
@AttributeOverrides 属性重写
@AttributeOverride 属性重写的内容和@AttributeOverrides一起嵌套使用
@SecondaryTables 多个表格映射
@SecondaryTable 定义辅助表格映射和@SecondaryTables一起嵌套使用
@GeneratedValue 标识符生成策略，默认Auto

表与表关系映射
@OneToOne：一对一映射。它包含五个属性：
targetEntity:关联的目标类
Cascade:持久化时的级联操作，默认没有
fetch:获取对象的方式，默认EAGER
Optional:目标对象是否允许为null，默认允许
mappedBy:定义双向关联中的从属类。
单向：
    @JoinColumn:定义外键(主表会多一字段，做外键)

@OneToMany：一对多映射；@ManyToOne：多对一映射
单向一对多：
    @OneToMany(cascade=CascadeType.ALL)
    @JoinColumn(name="book_oid")/**book：表；oid：book表的主键；无name会按此规则自动生成*/
单向多对一：
    @ManyToOne(cascade=CascadeType.ALL)
    @JoinColumn(name="author_oid")
关联表格一对多：
    @OneToMany(cascade=CascadeType.ALL)
    @JoinTable(joinColumn={@JoinColumn(name="BOOK_OBJECT_OID")},inverseJoinColumns={@JoinColumn(name="AUTHER_OBJECT_OID")})
双向一对多或多对一：
    不需要多一张表，只是使用mappedBy:使用在One一方，值为One方类名表示Many的从属类。

Java代码

@Entity
public class Org implements java.io.Serializable {
// Fields
@Id
@GeneratedValue
private String orgId;
private String orgName;
@OneToMany(mappedBy = "org")
private List<Department> departments;
// Constructors
...
// Property accessors
...
}

@Entity
public class Org  implements java.io.Serializable {


    // Fields    
	@Id
	@GeneratedValue
     private String orgId;
     private String orgName;
     @OneToMany(mappedBy = "org")
     private List<Department> departments;

    // Constructors
...
    // Property accessors
...
}

Java代码

@Entity
public class Department implements java.io.Serializable {
// Fields
@Id
@GeneratedValue
private String id;
private String name;
@ManyToOne(fetch=FetchType.EAGER)
@JoinColumn(name="org_orgId")
private Org org;
@OneToMany(mappedBy = "department")
private List<Employee> employees;
// Constructors
public List<Employee> getEmployees() {
return employees;
}
public void setEmployees(List<Employee> employees) {
this.employees = employees;
}
public Org getOrg() {
return org;
}
public void setOrg(Org org) {
this.org = org;
}
/** default constructor */
.
.
.
}

@Entity
public class Department  implements java.io.Serializable {


    // Fields    
	@Id
	@GeneratedValue
     private String id;
     private String name;
     @ManyToOne(fetch=FetchType.EAGER)
     @JoinColumn(name="org_orgId")
     private Org org;
     @OneToMany(mappedBy = "department")
     private List<Employee> employees;

    // Constructors

    public List<Employee> getEmployees() {
		return employees;
	}

	public void setEmployees(List<Employee> employees) {
		this.employees = employees;
	}

	public Org getOrg() {
		return org;
	}

	public void setOrg(Org org) {
		this.org = org;
	}

	/** default constructor */
             .
             .
             .
	
}

Java代码

@Entity
public class Employee implements java.io.Serializable {
// Fields
@Id
@GeneratedValue
private String employeeId;
private String employeeName;
private String passWord;
private Integer age;
private Integer sex;
@ManyToOne(fetch=FetchType.EAGER)
@JoinColumn(name="department_id")
private Department department;
public Department getDepartment() {
return department;
}
public void setDepartment(Department department) {
this.department = department;
}
/** default constructor */
...
// Property accessors
...
}

@Entity
public class Employee  implements java.io.Serializable {


    // Fields    
	@Id
	@GeneratedValue
     private String employeeId;
     private String employeeName;
     private String passWord;
     private Integer age;
     private Integer sex;
     @ManyToOne(fetch=FetchType.EAGER)
     @JoinColumn(name="department_id")
     private Department department;

     
    public Department getDepartment() {
		return department;
	}

	public void setDepartment(Department department) {
		this.department = department;
	}

	/** default constructor */
    ...
    // Property accessors
    ...
}

双向多对多：@ManyToMany.单向多对多这里不在赘述（没有太多实际意义）
这个比较简单，看下代码就明白了：

Java代码

@Entity
public class Book implements java.io.Serializable {
@Id
private int id;
private String name;
private float money;
@ManyToMany(cascade = CascadeType.ALL)
private List<Author> authors;
public List<Author> getAuthors() {
return authors;
}
public void setAuthors(List<Author> authors) {
this.authors = authors;
}
...
}

@Entity
public class Book  implements java.io.Serializable {
	@Id
	private int id;
	private String name;
	private float money;
	@ManyToMany(cascade = CascadeType.ALL)
	private List<Author> authors;
	

	public List<Author> getAuthors() {
		return authors;
	}
	public void setAuthors(List<Author> authors) {
		this.authors = authors;
	}
	
         ...
}

Java代码

@Entity
public class Author implements java.io.Serializable {
@Id
private int id;
private String name;
private int age;
@ManyToMany(mappedBy="authors")
private List<Book> books;
public List<Book> getBooks() {
return books;
}
public void setBooks(List<Book> books) {
this.books = books;
}
...
}

@Entity
public class Author  implements java.io.Serializable {
	@Id
	private int id;
	private String name;
	private int age;
	@ManyToMany(mappedBy="authors")
	private List<Book> books;
	

	public List<Book> getBooks() {
		return books;
	}

	public void setBooks(List<Book> books) {
		this.books = books;
	}

         ...
}

总算弄完了，不过还是一个皮毛！
需要注意的是：注释最好加在属性上，不要加在get方法上，那样做有时候就会出错。比如:@ManyToMany的时候就会报错！