Question

我创建了一个bean：

package beans;

import java.util.List;

import javax.ejb.LocalBean;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import mazeJPA.Forumcategory;

/**
 * Session Bean implementation class ForumBean
 */
@Stateless
@LocalBean
public class ForumBean
{

    @PersistenceContext(unitName = "mazeEJB")
    private EntityManager em;

    /**
     * Default constructor.
     */
    public ForumBean(){}


    public List<Forumcategory> getCategories()
    {
        return em.createNamedQuery
        (
                "Forumcategory.findAll", Forumcategory.class
        ).getResultList();
    }
}

及其实体类

package mazeJPA;

import java.io.Serializable;
import javax.persistence.*;


/**
 * The persistent class for the forumcategory database table.
 * 
 */
@Entity
@Table(name="forumcategory")
@NamedQuery(name="Forumcategory.findAll", query="SELECT f FROM Forumcategory f")
public class Forumcategory implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int cid;

    private String desc;

    private String name;

    public Forumcategory() {
    }

    public int getCid() {
        return this.cid;
    }

    public void setCid(int cid) {
        this.cid = cid;
    }

    public String getDesc() {
        return this.desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

当我从servlet调用getCategories（）时，我得到一个sql异常：

 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 'DESC, NAME FROM
 forumcategory' at line 1 Error Code: 1064 Call: SELECT CID, DESC, NAME
 FROM forumcategory Query: ReadAllQuery(name="Forumcategory.findAll"
 referenceClass=Forumcategory sql="SELECT CID, DESC, NAME FROM
 forumcategory")

我的表是：

  cid INT NOT NULL, name VARCHAR(255) NOT NULL, desc TEXT NOT NULL,
  PRIMARY KEY (cid)

我不知道为什么会这样。我的映射有问题吗？我最近才在我的项目中添加了这个与它有关的事项，即我是否必须立即生成所有表格？

Answer 1

DESC是一个 reserved sql word ，所以你必须使用desc来代替它，例如

SELECT CID, `DESC`, NAME FROM ...

Answer 2

DESC是大多数SQL中的保留关键字。似乎您的JPA提供程序不会为您自动转义这些（引号括起来）。一些JPA实现（例如DataNucleus JPA）为您做到了这一点。

尝试使用生成的命名查询时sqlException出错

2 个答案: