@ManyToOne + delete操作导致“not-null属性引用null或transient值”错误

Question

我有一个hibernate映射的数据结构，当我尝试删除它时会出错。

@Entity
@Table(name = "TYPE")
public class Type {
    @Id
    private int id;
    private String name;
}


@Entity
@Table(name = "BOOKS")
public class Book {

    @Id
    private int id;

    @ManyToOne(fetch = FetchType.EAGER, optional = false)
    private Type type;
}

当我尝试删除Book对象时，我得到了

Caused by: org.springframework.dao.DataIntegrityViolationException: not-null property references a null or transient value: com....Book.type; nested exception is org.hibernate.PropertyValueException: not-null property references a null or transient value: com...Book.type
    at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:645)
    at org.springframework.orm.hibernate3.HibernateAccessor.convertHibernateAccessException(HibernateAccessor.java:412)
    at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:424)
    at org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)
    at org.springframework.orm.hibernate3.HibernateTemplate.delete(HibernateTemplate.java:846)
    at org.springframework.orm.hibernate3.HibernateTemplate.delete(HibernateTemplate.java:842)

当我删除optional = false参数时，我看到Hibernate从TYPES表中删除了对象。如果有来自oposite端的ManyToOne链接，为什么它会尝试删除类型实体？ 感谢。

UPD： 父对象中提供书籍集合。要删除它，我使用以下代码：

Information info = getInformationById(id);
        if (info != null) {
            getHibernateTemplate().delete(info);
        }

upd2（完整层次结构）：

@Entity
@Table(name = "INFO")
public class Information {

    @Id
    @Column(name = "ID")
    private int id;

    @Version
    private int version;

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinColumn(name = "INFO_ID")
    private Set<Details> details;

...     }

@Entity
@Table(name = "DETAILS")
public class Details {

    @Id
    private int id;

    @Version
    private int version;

    @Column(name = "INFO_ID")
    private int infoId;

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinColumn(name = "DETAILS_ID", nullable = false)
    private Set<Books> books = new HashSet<Book>();

...     }

Chain is：Info-＆gt; Details-＆gt; Books。每本书都有一种类型，很可能是很多书都有相同的类型。我删除信息对象时，我不想删除类型实体。