hibernate 3 映射学习

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关键字: hibernate,annotation

基于注解的hibernate主键设置：@Id.
那么它的生成规则是什么呢？是由@GeneratedValue来规定的。

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！