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我正在學習Hibernate，並且我有一個關於基本HQL連接語法的問題。我正在關注這個tutorial。說我有一個產品和類別的實體，在hibernate HQL中指定連接條件「ON列」？
@Entity
@Table(name = "CATEGORY")
public class Category {
private long id;
private String name;
private Set<Product> products;
public Category() {
}
public Category(String name) {
this.name = name;
}
@Id
@Column(name = "CATEGORY_ID")
@GeneratedValue
public long getId() {
return id;
}
@OneToMany(mappedBy = "category", cascade = CascadeType.ALL)
public Set<Product> getProducts() {
return products;
}
// other getters and setters
}
@Entity
@Table(name = "PRODUCT")
public class Product {
private long id;
private String name;
private String description;
private float price;
private Category category;
public Product() {
}
public Product(String name, String description, float price,
Category category) {
this.name = name;
this.description = description;
this.price = price;
this.category = category;
}
@Id
@Column(name = "PRODUCT_ID")
@GeneratedValue
public long getId() {
return id;
}
@ManyToOne
@JoinColumn(name = "CATEGORY_ID")
public Category getCategory() {
return category;
}
// other getters and setters
}
所以我要加入類別和產品，我會像這樣在SQL
select * from Category A inner join Product B on A.id=B.category_id,
在HQL，似乎我們放棄了「開」的條件，上述查詢的HQL爲
String hql = "from Product p inner join p.category";
Query query = session.createQuery(hql);
爲什麼在HQL中不需要？