我正在使用 JPA (Hibernate)，当我尝试从数据库中获取对象时遇到问题。我正在使用 Glassfish 3.1.2、Hibernate 和 Oracle 数据库 10.2.0.4。
这是我的应用程序的概念：
答案是对表格的答案。一个表单属于一个类别。用户可以创建表单。用户可以回答。
所以：
- 1 个表格有一个类别，所以 1 个类别可能有多个表格
- 1 个答案有 1 个表格，1 个表格可能有多个答案
- 1 个回答有 1 个用户（回答作者）
- 1 个表单有 1 个用户（表单创建者）
如果我试图得到答案，我会得到一个错误（见帖子底部），但奇怪的是：
如果数据库中没有答案；它有效（至少没有抛出错误）
如果答案存在于数据库中且 answer.form_id 列中没有任何值；它有效（至少没有抛出错误）
如果我从答案类中删除表单属性并让用户属性；有用！答案是从数据库中获取的，并且还获取了用户。
如果我从答案类中删除用户属性并让表单属性；它失败！答案不是从数据库中得到的。（在本文末尾抛出错误）
如果我从表单类中删除类别和用户属性；有用！答案是从数据库中获取的，并且还获取了一个用户和一个表单！但是我不能这样，我需要在表单实体中有一个类别和一个用户。
如果我删除任一类别属性或任一用户属性，并让另一个在表单类中；它失败。
似乎 hibernate 无法获取比其他实体更远的信息：
- 回答 > 用户：好的
- 答案 > 没有类别或用户的表单：OK
- 表格 > 类别：OK
- 表单 > 用户：好的
- 答案 > 表格 > 类别：失败
- 答案 > 表格 > 用户：失败
但是我<property name="hibernate.max_fetch_depth" value="3"/>在我的persistence.xml 中设置。
有什么问题的任何想法或建议？它似乎是表单实体或其属性类别或用户。
谢谢
这是我的实际代码，为了清楚起见，大大减少了。
表格类：
@Entity
@Table(name="FORM")
public class Form implements Serializable {
private static final long serialVersionUID = -2101681231828548611L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO, generator = "G_FORM")
@SequenceGenerator(name = "G_FORM", sequenceName = "FORM_ID_SEQ")
@Column(name = "ID", unique = true, nullable = false)
private int id;
private String name;
@ManyToOne(cascade=CascadeType.ALL, fetch=FetchType.EAGER) @JoinColumn
private Category category;
@ManyToOne(cascade=CascadeType.ALL, fetch=FetchType.EAGER) @JoinColumn
private User user;
//more fields and usual getters and setters
}
用户等级：
@Entity
@Table(name = "USERS")
public class User implements Serializable {
private static final long serialVersionUID = -821421797110076396L;
@Id
@Column(name = "ID")
private String id;
@NotNull
@Column
private String email;
@NotNull
private String password;
@Column(name="PARENT_ID")
private User parent;
//more fields and usual getters and setters
}
答题类：
@Entity
public class Answer implements Serializable {
private static final long serialVersionUID = -8514559401482729639L;
@Id
@GeneratedValue(strategy = GenerationType.AUTO, generator = "G_ANSWER")
@SequenceGenerator(name = "G_ANSWER", sequenceName = "ANSWER_ID_SEQ")
@Column(name = "ID", unique = true, nullable = false)
private int id;
@ManyToOne(cascade=CascadeType.ALL, fetch=FetchType.EAGER) @JoinColumn
private Form form;
@ManyToOne(cascade=CascadeType.ALL, fetch=FetchType.EAGER) @JoinColumn
private User user;
//more fields and usual getters and setters
}
AnswerDAO 方法失败：
public List<Answer> getAllAnswers() throws Exception{
TypedQuery<Answer> query = em.createQuery( "SELECT a FROM Answer a ORDER BY a.id", Answer.class );
return query.getResultList();
//return em.createQuery("SELECT a FROM Answer a", Answer.class).getResultList();
}
在我的 persistence.xml 中：
<property name="hibernate.hbm2ddl.auto" value="update"/>
<property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/>
<property name="hibernate.show_sql" value="true"/>
<property name="hibernate.format_sql" value="true"/>
<property name="hibernate.max_fetch_depth" value="3"/>
hibernate生成的sql（似乎正确？）：
Infos: Hibernate: select answer0_.ID as ID1_0_, answer0_.ANSWER_XML as ANSWER2_0_, answer0_.DATE_UPLOAD as DATE3_0_, answer0_.form_ID as form4_0_, answer0_.user_ID as user5_0_ from Answer answer0_ order by answer0_.ID
Infos: Hibernate: select form0_.ID as ID1_2_2_, form0_.category_NAME as category6_2_2_, form0_.DATE_UPLOAD as DATE2_2_2_, form0_.extention as extentio3_2_2_, form0_.name as name4_2_2_, form0_.QUESTION_XML as QUESTION5_2_2_, form0_.user_ID as user7_2_2_, category1_.NAME as NAME1_1_0_, category1_.DATE_CREATION as DATE2_1_0_, user2_.ID as ID1_5_1_, user2_.ANSWER_COUNT as ANSWER2_5_1_, user2_.DATE_INSCRIPTION as DATE3_5_1_, user2_.DATE_LAST_ANSWER as DATE4_5_1_, user2_.DATE_LAST_LOGIN as DATE5_5_1_, user2_.email as email6_5_1_, user2_.firstname as firstnam7_5_1_, user2_.FORM_COUNT as FORM8_5_1_, user2_.lastname as lastname9_5_1_, user2_.PARENT_ID as PARENT10_5_1_, user2_.password as passwor11_5_1_ from FORM form0_ left outer join Category category1_ on form0_.category_NAME=category1_.NAME left outer join USERS user2_ on form0_.user_ID=user2_.ID where form0_.ID=?
Eclipse 控制台中的错误也大大减少了：
WARN: SQL Error: 17027, SQLState: null
ERROR: Le flux de données est déjà fermé
Infos: HHH000327: Error performing load command : org.hibernate.exception.GenericJDBCException: could not load an entity: [be.adehis.bean.Form#96]
Avertissement: EJB5184:A system exception occurred during an invocation on EJB AnswerDAO, method: public java.util.List be.adehis.database.dao.AnswerDAO.getAllAnswers() throws java.lang.Exception
Avertissement: javax.ejb.TransactionRolledbackLocalException: Exception thrown from bean
at ...
Caused by: javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: could not load an entity: [be.adehis.bean.Form#96]
at ...
Caused by: org.hibernate.exception.GenericJDBCException: could not load an entity: [be.adehis.bean.Form#96]
at ...
Caused by: java.sql.SQLException: Le flux de données est déjà fermé
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:113)
Avertissement: EJB5184:A system exception occurred during an invocation on EJB AnswerService, method: public java.util.List be.adehis.service.answer.AnswerService.getAllAnswers() throws java.lang.Exception
Avertissement: javax.ejb.EJBTransactionRolledbackException
at ...
Caused by: javax.ejb.TransactionRolledbackLocalException: Exception thrown from bean
at ...
Caused by: javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: could not load an entity: [be.adehis.bean.Form#96]
at ...
Caused by: org.hibernate.exception.GenericJDBCException: could not load an entity: [be.adehis.bean.Form#96]
at ...
Caused by: java.sql.SQLException: Le flux de données est déjà fermé