Hibernate 注解 的问题求解

Question

有类A与类B多对多映射，
类A代码
[code="java"]
@Entity

@Table(name="a")
public class A {
@Id

@GeneratedValue

private Integer id;
private String name;

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

@ManyToMany(cascade={CascadeType.MERGE,CascadeType.PERSIST}
)  
@JoinTable(name="a_b",  
           joinColumns={@JoinColumn(name="a_id")},  
           inverseJoinColumns={@JoinColumn(name="b_id")}  
)  
private List<B> bs;

public List<B> getBs() {
    return bs;
}

public void setBs(List<B> bs) {
    this.bs = bs;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

}[/code]
类B代码
[code="java"]
@Entity
@Table(name = "b")
public class B {
@Id
@GeneratedValue
private Integer id;
private String name;

@ManyToMany(cascade = { CascadeType.PERSIST, CascadeType.MERGE }, mappedBy = "bs", targetEntity = A.class)
private List<A> as;

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

public List<A> getAs() {
    return as;
}

public void setAs(List<A> as) {
    this.as = as;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

}
[/code]

现在的问题是：
A a1 = (A)session.get(A.class, 1);
System.out.println(a1.getBs().size());
可以正常通过A获得B

B b1 = (B)session.get(B.class, 1);
System.out.println(b1.getAs().size());
但不能通过如上代码 通过B获得A

Answer 1

http://docs.jboss.org/hibernate/stable/annotations/reference/en/html_single/#entity-mapping-association

看 2.2.5.3.2. Many-to-many

应该能解决你的问题了。

这个文档应该比我说的清楚。