使用annotation配置hibernate（2）：一对多关系配置

数据表结构

 

单向一对多

Student.java

@Entity
@Table(name = "student")
public class Student {
    @Id
    @Column(name = "id")
    @GenericGenerator(name = "generator",strategy = "native")
    @GeneratedValue(generator = "generator")
    private int id;
    
    @Column(name = "name")
    private String name;
    
    @ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
    @JoinColumn(name="grade_id")
    private Grade grade;
}

Grade.java

@Entity
@Table(name="grade")
public class Grade {
    @Id
    @Column(name = "id")
    @GenericGenerator(name = "generator", strategy = "native")
    @GeneratedValue(generator = "generator")
    private int id;
    
    @Column(name = "name")
    private String name;
}

单向多对一

Student.java

@Entity
@Table(name = "student")
public class Student {
    @Id
    @Column(name = "id")
    @GenericGenerator(name = "generator",strategy = "native")
    @GeneratedValue(generator = "generator")
    private int id;
    
    @Column(name = "name")
    private String name;
    
    @ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
    @JoinColumn(name="grade_id")
    private Grade grade;
}

  Grade.java

@Entity
@Table(name="grade")
public class Grade {
    @Id
    @Column(name = "id")
    @GenericGenerator(name = "generator", strategy = "native")
    @GeneratedValue(generator = "generator")
    private int id;
    
    @Column(name = "name")
    private String name;
}

双向关联

Student.java

@Entity
@Table(name = "student")
public class Student {
    @Id
    @Column(name = "id")
    @GenericGenerator(name = "generator",strategy = "native")
    @GeneratedValue(generator = "generator")
    private int id;
    
    @Column(name = "name")
    private String name;
    
    @ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
    @JoinColumn(name="grade_id")
    private Grade grade;
}

 Grade.java

@Entity
@Table(name="grade")
public class Grade {
    @Id
    @Column(name = "id")
    @GenericGenerator(name = "generator", strategy = "native")
    @GeneratedValue(generator = "generator")
    private int id;
    
    @Column(name = "name")
    private String name;
    
    @OneToMany(cascade=CascadeType.ALL,fetch=FetchType.EAGER,mappedBy="grade")
    private Set<Student> students = new HashSet<Student>(); 
}

  

自身一对多

Category.java

@Entity
@Table(name = "category")
public class Category {
    @Id
    @Column(name = "id")
    @GenericGenerator(name = "generator",strategy = "native")
    @GeneratedValue(generator = "generator")
    private int id;
    
    @OneToMany(cascade=CascadeType.ALL,fetch=FetchType.LAZY,mappedBy="category")
    private Set<Category> categorys = new HashSet<Category>();
    
    @ManyToOne(cascade=CascadeType.ALL,fetch=FetchType.EAGER)
    @JoinColumn(name="father_category")
    private Category category;

}

关于mappedBy关键字的具体作用可以参考 http://xiaoruanjian.iteye.com/blog/1094253