使用 JPA 连接两个表

Question

我正在尝试使用 @NamedQuery 连接两个表，Address 和 Division。同一地址有多个部门。目前我有
Division.java:

@Entity
@Table(name="division")
@NamedQuery(name="Division.mailingAddress", query="SELECT d, a from Division d LEFT JOIN d.addresses a")
public class Division implements Serializable{
    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @Column(name="division_id")
    private Short divisionId;

    @Basic(optional = false)
    @Column(name="division_name")
    private String divisionName;

    @Basic(optional = false)
    @Column(name="address_id")
    private Short addressId;

    @OneToMany(mappedBy="divisionMailingAddress")
    private List<Address> addresses;

    //getters and setters
}

Addresses.java:

@Entity
@Table(name="address")
public class Address implements Serializable{
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GeneratedType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "address_id")
    private Short addressID;

    @Basic(optional = false)
    @Column(name = "mailing_address")
    private String mailingAddress;

    @ManyToOne
    private Division divisionMailingAddress;
}

我在运行时得到的错误是： Unknown column 't0.DIVISIONMAILINGADDRESS_division_id' in 'on clause'

我想要得到的是在 MySQL 中有效的这一行： SELECT * FROM (division d join address a on d.address_id = a.address_id);
目前 JPA 正在将命名查询解析为：
SELECT t1."all columns", t0."all columns" from division t1 LEFT OUTER JOIN address t0 ON (t0.DIVISIONMAILINGADDRESS_division_id = t1.division_id) 我在做什么有什么问题？ JPA 是否希望连接来自地址而不是部门？我如何获得 address_id 与 division_id 之间的通话？

更新：

在大力帮助下，这两个类已被更改以实现我想要的结果。

Division.java:

@Entity
@Table(name="division")
@NamedQuery(name="Division.mailingAddress", query="SELECT d from Division d LEFT JOIN d.addressesM2O a")
public class Division implements Serializable{
    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @Column(name="division_id")
    private Short divisionId;

    @Basic(optional = false)
    @Column(name="division_name")
    private String divisionName;

    @Basic(optional = false)
    @Column(name="address_id")
    private Short addressId;

    @ManyToOne(targetEntity = Address.java)
    @JoinColumn(name = "address_id", updatable=false, insertable=false)
    private Address addressesM2O;

    //getters and setters
}

Address.java:

@Entity
@Table(name="address")
public class Address implements Serializable{
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GeneratedType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "address_id")
    private Short addressID;

    @Basic(optional = false)
    @Column(name = "mailing_address")
    private String mailingAddress;

    @OneToMany(mappedBy="addressesM2O")
    private List<Division> divisionO2M;
}

@NamedQuery 已更改，因为 d 和 a 的存在使结果列表 return 成为 Object[] 的列表。 Division 和 Address 是对象。这就是为什么 d 被保留而 a 从 @NamedQuery.

中删除的原因

Answer 1

我认为问题是您在地址 class 中提到 @ManyToOne 时没有提到 @JoinColumn ，因此在进行连接时 JPA 本身正在创建外部键 DIVISIONMAILINGADDRESS_division_id.

尝试在地址 class 中提及 ManyToOne 关系，如有任何问题请告诉我：

@ManyToOne(targetEntity = Division.class)
@JoinColumn(name= "division_id")//basically the name of the column here should be same as the one mentioned in your database

Answer 2

对我有用的是将 @OneToMany 和 @ManyToOne 更改为 @OneToOne，在 address table 中使用 @PrimaryKeyJoinColumn。代码更新如下： Division.java 更改为：

@OneToOne(mappedBy="divisionMailingAddress")
private Address address;

Address.java改为：

@OneToOne
@PrimaryKeyJoinColumn
private Division divisionMailingAddress;

使用 JPA 连接两个表

Joining two tables with JPA

netbeans

jpa

named-query

eclipselink

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