使用HSQL检索数据-多对一关系

Question

I define the following entities : BaseEntity , magasin and article :

 @Entity(name = "magasin")
@Table(name = "magasin")
public class Magasin extends BaseEntity {

    private static final long serialVersionUID = 1L;


    @Basic
    @Size(min=5, max=100, message="The name must be between {min} and {max} characters")
    private String name;

    @OneToMany(cascade=CascadeType.ALL, mappedBy="magasin")
    @Valid
    private Set<Article> article;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Set<Article> getArticle() {
        return article;
    }

    public void setArticle(Set<Article> article) {
        this.article = article;
    }
}

@Entity(name="article")
@Table(name="article")
public class Article extends BaseEntity {

    private static final long serialVersionUID = 1L;

    @ManyToOne
    private Magasin magasin;

    @Basic
    @Size(min=5, max=100, message="The name must be between {min} and {max} characters")
    private String name;
    @Basic
    private float price;

    public Magasin getMagasin() {
        return magasin;
    }

    public void setMagasin(Magasin magasin) {
        this.magasin = magasin;
    }

    public String getName() {
        return name;
    }

    public void setName(String nom) {
        this.name = nom;
    }
    public float getPrice() {
        return price;
    }

    public void setPrice(float price) {
        this.price = price;
    }

}

 @MappedSuperclass
 public class BaseEntity {

@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Integer id;

public void setId(Integer id) {
    this.id = id;
}

public Integer getId() {
    return id;
}

public boolean isNew() {
    return (this.id == null);
}

}

How can create a hql query in order to retrieve all Article for a magasin selected ?

I try this

 @Override
public List<Article> findArticle(Magasin magasin) {
    String query = "From Article m where m.magasin.id = "+magasin.getId();
    System.out.print(query);
    Session session = getSessionFactory().getCurrentSession();
    if((session.createQuery(query).list()!=null) && (session.createQuery(query).list().size()!=0))
        return (List<Article>) session.createQuery(query).list();
    else
        return null;
  }

But it returns nothing , always null .How can I resolve it ?

Answer 1

尝试以下操作：“选择* From Article，Mgasin，其中Article.mgasin.id =“ + magasin.getId（）;

Answer 2

I don't know the type of your magasin id so adapt the code below.

First get the Magasin instance for the id:

Magasin mag = (Magasin)session.get(Magasin.class, id);

Next you can access the articles for the magasin mag via accessor

Set<Article> articles = mag.getArticle();