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
- 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=""customer""/>
- 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=""customer""/>
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 { ... }
- 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: