jpql從表中選擇對象基於另一個表的某些屬性？

Question

我是jpql的新手。 我有兩個mySql表。 表廣告：與列：

ID，名稱，描述，電話號碼，類別等。

並表advert_property與下列：

id   int 11 
advert_id int 11 
name  varchar 255 
value  varchar 255  
descr  varchar 255 

我的目標是選擇來自表advert的對象，其中有一個屬性category = "flats"寫在表advert屬性名稱number_rooms = "234"寫在表advert_property。

我很困惑與JPQL大成一點點我來到這個解決方案：

Query q = em.createQuery("SELECT ap FROM AdvertProperty as ap, Advert as a " 
+ " where a.category= 'flats' and ap.advertId = a.id and ap.name='number_rooms' "); 

List<Advert> ads = q.getResultList(); 

但因爲我需要它不工作..

請建議， 感謝

廣告實體：

public class Advert implements Serializable { 
private static final long serialVersionUID = 1L; 
@Id 
@GeneratedValue(strategy = GenerationType.IDENTITY) 
@Basic(optional = false) 
private Integer id; 
@Size(max = 255) 
private String title; 
@Lob 
@Size(max = 65535) 
private String content; 
private Integer price; 
@Size(max = 255) 
@Column(name = "contact_person") 
private String contactPerson; 
// @Pattern(regexp="[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?", message="Invalid email")//if the field contains email address consider using this annotation to enforce field validation 
@Size(max = 255) 
private String email; 
// @Pattern(regexp="^\\(?(\\d{3})\\)?[- ]?(\\d{3})[- ]?(\\d{4})$", message="Invalid phone/fax format, should be as xxx-xxx-xxxx")//if the field contains phone or fax number consider using this annotation to enforce field validation 
@Size(max = 255) 
private String phone; 
@Column(name = "address_id") 
private Integer addressId; 
@Column(name = "category_id") 
private Integer categoryId; 
@Basic(optional = false) 
@NotNull 
@Column(name = "company_type") 
private boolean companyType; 
@Basic(optional = false) 
@NotNull 
private boolean approved; 
@Column(name = "user_id") 
private Integer userId; 
@Column(name = "who_can_watch") 
private Integer whoCanWatch; 
@Basic(optional = false) 
@NotNull 
@Column(name = "creation_date") 
@Temporal(TemporalType.TIMESTAMP) 
private Date creationDate; 
@Size(max = 255) 
private String razdel; 

public Advert() { 
} 

public Advert(Integer id) { 
    this.id = id; 
} 

AdvertProperty實體：

@Entity 
@Table(name = "advert_property") 
@XmlRootElement 
@NamedQueries({ 
    @NamedQuery(name = "AdvertProperty.findAll", query = "SELECT a FROM AdvertProperty a"), 
    @NamedQuery(name = "AdvertProperty.findById", query = "SELECT a FROM AdvertProperty a WHERE a.id = :id"), 
    @NamedQuery(name = "AdvertProperty.findByAdvertId", query = "SELECT a FROM AdvertProperty a WHERE a.advertId = :advertId"), 
    @NamedQuery(name = "AdvertProperty.findByName", query = "SELECT a FROM AdvertProperty a WHERE a.name = :name"), 
    @NamedQuery(name = "AdvertProperty.findByValue", query = "SELECT a FROM AdvertProperty a WHERE a.value = :value"), 
    @NamedQuery(name = "AdvertProperty.findByDescr", query = "SELECT a FROM AdvertProperty a WHERE a.descr = :descr")}) 
public class AdvertProperty implements Serializable { 
    private static final long serialVersionUID = 1L; 
    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    @Basic(optional = false) 
    private Integer id; 
    @Column(name = "advert_id") 
    private Integer advertId; 
    @Size(max = 255) 
    private String name; 
    @Size(max = 255) 
    private String value; 
    @Size(max = 255) 
    private String descr; 

Answer 1

編輯

既然你已經從advert_property到advert外鍵，你可以模擬你的實體相應

在廣告實體

... 
@OneToOne(mappedBy = "advert") 
private AdvertProperty property; 
// or this, in case it is one to many 
@OneToMany(mappedBy = "advert") 
private List<AdvertProperty> properties; 
... 

在AdvertPropert Ÿ實體

@ManyToOne // or @OneToOne 
@JoinColumn("advert_id") 
private Advert advert; 

如果它是@OneToMany，查詢應該是這樣的

Query q = em.createQuery("SELECT a FROM Advert a join a.properties p where a.category = 'flats' and p.name='number_rooms' "); 

如果它是@OneToOne，查詢應該是這樣的

Query q = em.createQuery("SELECT a FROM Advert a where a.category = 'flats' and a.property.name='number_rooms' "); 

Answer 2

視你如何實現你的實體：

SELECT a FROM Advert a JOIN a.properties ap where a.category = 'flats' and ap.name='number_rooms' 

或

SELECT a FROM AdvertPropery ap JOIN ap.advert where a.category = 'flats' and ap.name='number_rooms' 

但是發表您的實體有一個確切的答案。

---

那不是如何JPA是應該做的一個映射，你應該使用關係註釋（@OneToMany，@ManyToOne，...）和映射註釋（@JoinColumn，@JoinTable，...）

無關係（和索引！），你唯一可以做的查詢是類似於您剛纔所做的事情：

SELECT DISTINCT ap FROM AdvertProperty ap, Advert a where a.category= 'flats' and ap.advertId = a.id and ap.name='number_rooms' 

不過這查詢不優化的（沒有索引...）和有一個非常糟糕的表現。