JPA：当我尝试坚持一个对象时奇怪的错误 [英] JPA: Weird error when I try to persist an object

问题描述

User 和 Group 之间的 OneToMany 关系>

Group.java

  @Entity 
 public class Group {
 
 @Id 
 @GeneratedValue（strategy = GenerationType.AUTO）
 private Long id; 
 
私人字符串groupid; 
 
 @ManyToOne 
 @JoinColumn（name =USER_FK）
私人用户用户; 
 ... 
} 
  

User.java

  @Entity 
 public class User {
 
 @ Id 
 @GeneratedValue（strategy = GenerationType.AUTO）
 private Long id; 
 
 private String userId; 
 
私人字符串密码; 
 
 private String fname; 
 
 private String lname; 
 
 @OneToMany（mappedBy =user，cascade = CascadeType.ALL）
 private List< Group>组; 
 $ b public void addGroup（Group group）{
 if（this.groups == null）{
 this.groups = new ArrayList< Group>（）; 
} 
 this.groups.add（group）; 
 group.setUser（this）; 
 
 
 
 
 
 
 $ b 
所以当我尝试坚持对象
  User user = em.find（User.class，1L）; 
 user.addGroup（group）; 
 persist（user）; 
  
我得到了这个 
 
 
 （Eclipse持久性服务 -  2.0.1.v20100213-r6600）：org.eclipse.persistence.exceptions.DatabaseException 
内部异常：com.mysql.jdbc.exceptions。 jdbc4.MySQLSyntaxErrorException：您的SQL语法有错误;检查与您的MySQL服务器版本相对应的手册，以便在第1行的GROUP（ID，GROUPID，USER_FK）VALUES（2501，'fdsaf'，1）'附近使用正确的语法
错误代码：1064 
调用：INSERT INTO GROUP（ID，GROUPID，USER_FK）VALUES（？，？，？）
 bind => [2501，fdsaf，1] 
查询：InsertObjectQuery（org.xdrawings.entity.Group@a1c）
  
正如你所看到的，它试图插入正确的值，但不知何故它被标记为语法错误。我认为它缺少单引号围绕 GROUP ，但由于它在底层查询，我不知道如何解决它。请注意，我对同一个项目中的其他实体做了完全相同的事情，并且工作正常。所以很沮丧！         GROUP确实是一个保留关键字，你必须转义它。在JPA 2.0中，有一种标准化的方式来指定分隔标识符。从JPA 2.0规范：
 $ b 
 
 
 2.13数据库对象的命名
 
 
 
 ..  
 
 
要指定分隔标识符，必须使用以下方法之一：
 
 
 
 
可以指定将持久化单元中使用的所有数据库标识符视为分隔标识符，方法是在
 
中指定< delimited-identifiers /> code> persistence-unit-defaults 元素的对象/关系xml映射文件。如果指定了< delimited-identifiers /> 元素，则不能被覆盖。
 
 
数据库对象的名称将被解释为分隔标识符，如下所示：
 
 
 
 
使用注释，名称被指定为分隔符标识符通过将名称
包含在双引号中，从而内部引号将被转义，例如 @Table（name =\customer \） 。 使用XML时，通过使用双
引号将名称指定为分隔标识符，例如< table name =& quot; quot ;客户& quot; />  
 
  
  
 
 $ b 
所以像这样的东西应该工作：
 
 $ $ p $ $ $ c $ @Entity 
 @Table =\GROUP \）
 public class Group {
 ... 
} 
  

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);
}
}

So when I try to persist the object

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

I got this

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)

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 !!

解决方案

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:

2.13 Naming of Database Objects

...

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

• 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;"/>

So something like this should work:

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

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