JPA:尝试持久化对象时出现奇怪的错误

JPA: Weird error when I try to persist an object(JPA:尝试持久化对象时出现奇怪的错误)

问题描述

我得到了 User 和 Group 之间的 OneToMany 关系
Group.java

I got a OneToMany relation between User and Group
Group.java

@Entity
public class Group {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)        
private Long id;

private String groupid;

@ManyToOne
@JoinColumn(name="USER_FK")
private User user;
...
}

User.java

@Entity
public class User {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)    
private Long id;

private String userId;

private String password;

private String fname;

private String lname;

@OneToMany(mappedBy="user", cascade=CascadeType.ALL)
private List<Group> groups;

public void addGroup(Group group){
    if(this.groups == null){
        this.groups = new ArrayList<Group>();
    }
    this.groups.add(group);
    group.setUser(this);
}
}

所以当我尝试持久化对象时

So when I try to persist the object

    User user = em.find(User.class, 1L);
    user.addGroup(group);
    persist(user);

我知道了

Exception [EclipseLink-4002] (Eclipse Persistence Services - 2.0.1.v20100213-r6600): org.eclipse.persistence.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'GROUP (ID, GROUPID, USER_FK) VALUES (2501, 'fdsaf', 1)' at line 1
Error Code: 1064
Call: INSERT INTO GROUP (ID, GROUPID, USER_FK) VALUES (?, ?, ?)
bind => [2501, fdsaf, 1]
Query: InsertObjectQuery(org.xdrawings.entity.Group@a1c)

如您所见，它尝试插入正确的值，但不知何故将其标记为语法错误.我认为它缺少 GROUP 周围的单引号，但由于它在后台进行查询，我不知道如何修复它.请注意，我对同一项目中的其他实体做了完全相同的事情，并且效果很好.好郁闷！！

As you can see, it try to insert the correct values, but somehow it marked as syntax error. I think it missing single quote around GROUP, but since it does the query under the hood, I have no idea how to fix it. Note that I did the exact same thing to with other entity in the same project and it works fine. So frustrated !!

推荐答案

GROUP 确实是保留关键字，您必须将其转义.在 JPA 2.0 中，有一种指定分隔标识符的标准化方法.来自 JPA 2.0 规范:

GROUP is indeed a reserved keyword, you'll have to escape it. In JPA 2.0, there is a standardized way to specify delimited identifiers. From the JPA 2.0 specification:

...

要指定分隔标识符，必须使用以下方法之一:

To specify delimited identifiers, one of the following approaches must be used:

• 可以通过在 persistence-unit 中指定 元素来指定将用于持久性单元的所有数据库标识符视为分隔标识符-defaults 对象/关系 xml 映射文件的元素.如果指定了 <delimited-identifiers/> 元素，则不能被覆盖.
• 可以基于每个名称指定将数据库对象的名称解释为分隔标识符，如下所示:
  • 使用注解，通过将名称括起来，将名称指定为分隔标识符在双引号内，其中内引号被转义，例如 @Table(name=""customer"").
  • 使用 XML 时，名称通过使用 double 指定为分隔标识符引号，例如 <table name="&quot;customer&quot;"/>
  • It is possible to specify that all database identifiers in use for a persistence unit be treated as delimited identifiers by specifying the <delimited-identifiers/> element within the persistence-unit-defaults element of the object/relational xml mapping file. If the <delimited-identifiers/> element is specified, it cannot be overridden.
  • It is possible to specify on a per-name basis that a name for a database object is to be interpreted as a delimited identifier as follows:
    • Using annotations, a name is specified as a delimited identifier by enclosing the name within double quotes, whereby the inner quotes are escaped, e.g., @Table(name=""customer"").
    • When using XML, a name is specified as a delimited identifier by use of double quotes, e.g., <table name="&quot;customer&quot;"/>

    所以这样的事情应该可以工作:

    So something like this should work:

    @Entity
    @Table(name=""GROUP"")
    public class Group {
        ...
    }
    

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