JPA：查询以根据实体类中定义的外键值获取结果？

Posted 2023-02-26

【中文标题】JPA：查询以根据实体类中定义的外键值获取结果？

【英文标题】：JPA: query to get results based on value of foreign key defined in the entity class?

【发布时间】：2011-05-09 23:16:34

【问题描述】：

Netbean 6.9 从此 SQL Server 2008 表生成以下 JPA 实体类：

我想获取所有具有特定 SKU 值的 ProductDescriptor。像这样的：

SELECT * FROM ProductDescriptors WHERE SKU='something'

给定实体类，获取结果的 Java 代码是什么？

谢谢。

@Entity
@Table(name = "ProductDescriptors")
@NamedQueries(
    @NamedQuery(name = "ProductDescriptors.findAll",     query = "SELECT p FROM ProductDescriptors p"),
    @NamedQuery(name = "ProductDescriptors.findByDescriptorID", query = "SELECT p FROM ProductDescriptors p WHERE p.descriptorID = :descriptorID"),
    @NamedQuery(name = "ProductDescriptors.findByLanguageCode", query = "SELECT p FROM ProductDescriptors p WHERE p.languageCode = :languageCode"),
    @NamedQuery(name = "ProductDescriptors.findByTitle", query = "SELECT p FROM ProductDescriptors p WHERE p.title = :title"),
    @NamedQuery(name = "ProductDescriptors.findByIsDefault", query = "SELECT p FROM ProductDescriptors p WHERE p.isDefault = :isDefault"),
    @NamedQuery(name = "ProductDescriptors.findByBody", query = "SELECT p FROM ProductDescriptors p WHERE p.body = :body"))
public class ProductDescriptors implements Serializable 
    private static final long serialVersionUID = 1L;
    @Id
    @Basic(optional = false)
    @Column(name = "DescriptorID")
    private Integer descriptorID;
    @Basic(optional = false)
    @Column(name = "LanguageCode")
    private String languageCode;
    @Basic(optional = false)
    @Column(name = "Title")
    private String title;
    @Basic(optional = false)
    @Column(name = "IsDefault")
    private boolean isDefault;
    @Basic(optional = false)
    @Column(name = "Body")
    private String body;
    @JoinColumn(name = "SKU", referencedColumnName = "SKU")
    @ManyToOne(optional = false)
    private Products products;

...

【参考方案1】：

类似这样的：

@PersistenceContext( unitName = "youPersistenceUnitHere" )
private EntityManager _entityManager;

public List<ProductDescriptors> getProductDescriptorsBySku( String sku ) 
   Query query = _entityManager.createQuery( "Select ProductDescriptors from ProductDescriptors pd where pd.products.sku = ?1" );
   query.setParameter( 1, sku );
   return new ArrayList<ProductDescriptors>( query.getResultList() );

【讨论】：

另一个有点类似的问题：***.com/questions/4180905/jpa-join-table-syntax

好的，我在那里添加了一个解决方案。正如我在那里评论的那样，我不知道您需要涉及 products 表\实体集；所以我把它留了下来。如果你这样做，请发表评论，我会再看一遍。