我正在使用JPA开发我的第一个项目,数据库使用MySQL,JPA提供程序为Hibernate 4.3.8,这是一个基于Spring 4的Web项目。
在我的Spring配置文件中,我设置了数据库和方言:
HibernateJpaVendorAdapter hjpaVA = new HibernateJpaVendorAdapter();
hjpaVA.setDatabase(Database.MYSQL);
hjpaVA.setDatabasePlatform("org.hibernate.dialect.MySQL5Dialect");
我尝试获取这个让我困扰的查询:
TypedQuery<KundeDTO> query = entityManager.createQuery("select new zdb.dto.KundeDTO(k.id, k.firma.firmenname, k.regnr, k.kategorie)
from Kunde k where k.id = :id", KundeDTO.class);
这是Hibernate生成的SQL语句:
select kunde0_.`id` as col_0_0_, firma1_.`firmenname` as col_1_0_, kunde0_.`regnr` as col_2_0_, kunde0_.id_kategorie as col_3_0_
from `zdb_e`.`Kunde` kunde0_, `zdb_e`.`Firma` firma1_
inner join `zdb_e`.`Kategorie` kategorie2_ on kunde0_.id_kategorie=kategorie2_.`id`
where kunde0_.id_firma=firma1_.`id` and kunde0_.`id`=1;
请注意,内连接上没有括号!
运行此语句会导致以下错误:
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException:
Unknown column 'kunde0_.id_kategorie' in 'on clause'
异常的原因在这里有详细说明:mysql-unknown-column-in-on-clause。
当我给where和内连接子句添加括号并直接对数据库运行该语句时,它就可以正常工作:
select kunde0_.`id` as col_0_0_, firma1_.`firmenname` as col_1_0_, kunde0_.`regnr` as col_2_0_, kunde0_.id_kategorie as col_3_0_
from (`zdb_e`.`Kunde` kunde0_, `zdb_e`.`Firma` firma1_ )
inner join `zdb_e`.`Kategorie` kategorie2_ on
( kunde0_.id_kategorie=kategorie2_.`id` )
where kunde0_.id_firma=firma1_.`id` and kunde0_.`id`=1;
那么,我该如何说服Hibernate生成这样的查询呢?
更新:以下是实体
客户
@Entity
public class Kunde implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
private Integer id;
private Integer regnr;
@OneToOne(optional=false)
@JoinColumn(name="id_firma", nullable = false)
private Firma firma;
@OneToOne(optional=false)
@JoinColumn(name="id_kategorie", nullable = false)
private Kategorie kategorie;
@OneToOne(optional=false)
@JoinColumn(name="id_lieferregion", nullable = false)
private Lieferregion lieferregion;
// getters and setters....
}
公司
@Entity
@Table(name = "Firma")
public class Firma implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
private Integer id;
@Column(name="firmenname")
private String firmenname;
@Column(name="uid")
private String uid;
@OneToOne(optional=false)
@JoinColumn(name="id_anschrift", nullable = false)
private Anschrift anschrift;
@OneToMany(mappedBy="id_firma", fetch=FetchType.EAGER)
private List<Person> personen;
public Firma() {
personen = new ArrayList<Person>();
}
// getters and setters....
}
Category
@Entity
public class Kategorie implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue
private Integer id;
private Integer nummer;
private String bezeichnung;
public Kategorie() {
}
public Kategorie(int kategorieId, int kategorieNummer, String kategorieBezeichnung) {
this.id = kategorieId;
this.nummer = kategorieNummer;
this.bezeichnung = kategorieBezeichnung;
}
// getters and setters....
}
数据库模式
CREATE TABLE kategorie
(id INTEGER NOT NULL AUTO_INCREMENT,
nummer INTEGER NOT NULL,
bezeichnung VARCHAR(100) NOT NULL,
PRIMARY KEY (id),
UNIQUE (nummer, bezeichnung)
);
CREATE TABLE firma
(ID INTEGER NOT NULL AUTO_INCREMENT,
firmenname VARCHAR(50) NOT NULL,
uid VARCHAR(20) NOT NULL,
url VARCHAR(100) NOT NULL,
id_anschrift INTEGER NOT NULL,
id_logo INTEGER,
PRIMARY KEY (id),
UNIQUE (uid),
UNIQUE (firmenname),
UNIQUE (id_anschrift),
CONSTRAINT firma_fk1 FOREIGN KEY (id_anschrift) REFERENCES ANSCHRIFT (ID),
CONSTRAINT firma_fk2 FOREIGN KEY (id_logo) REFERENCES logo (ID));
CREATE TABLE kunde
(id INTEGER NOT NULL AUTO_INCREMENT,
regnr INTEGER NOT NULL,
id_kategorie INTEGER NOT NULL,
id_firma INTEGER NOT NULL,
id_benutzer INTEGER,
id_lieferregion INTEGER NOT NULL,
PRIMARY KEY (id),
UNIQUE (regnr, id_kategorie),
UNIQUE (id_firma),
UNIQUE (id_benutzer),
CONSTRAINT kunde_fk1 FOREIGN KEY (id_firma) REFERENCES firma (id),
CONSTRAINT kunde_fk2 FOREIGN KEY (id_benutzer) REFERENCES benutzer (id),
CONSTRAINT kunde_fk3 FOREIGN KEY (id_kategorie) REFERENCES kategorie (id),
CONSTRAINT kunde_fk4 FOREIGN KEY (id_lieferregion) REFERENCES lieferregion (id)
);
经进一步测试
问题在于from子句缺少括号。
直接访问数据库:
select k.id, k.regnr, f.firmenname from (Kunde k, Firma f) JOIN kategorie kat on k.id_kategorie = kat.id where k.id = 1 and k.id_firma = f.id;
运作良好!
select k.id, k.regnr, f.firmenname from Kunde k, Firma f JOIN kategorie kat on k.id_kategorie = kat.id where k.id = 1 and k.id_firma = f.id;
无法工作:在“on子句”中未知列“k.id_kategorie”
为什么我甚至需要在from子句中使用括号?
如何让Hibernate自动添加它们?
AND
,而错误明显是关于不存在的列。请检查您的数据库架构。 - JB Nizet