0

我有一对多拥有的关系。这是我的父类：

@XmlRootElement
@Entity
public class Strip {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;

private long id;
private String filename = "";

@OneToMany(mappedBy = "strip", cascade = CascadeType.ALL)
private List<Quote> quotes = new ArrayList<Quote>();

public long getId() {
    return key.getId(); 
}

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

public String getFilename() {
    return filename;
}
public void setFilename(String filename) {
    this.filename = filename;
}

public List<Quote> getQuotes() {
    return quotes;
}

public void setQuotes(List<Quote> quotes) {
    this.quotes = quotes;
}

public Key getKey() {
    return key;
}
}

和子班：

@XmlRootElement
@Entity
public class Quote {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Key key;

private long id;

private String quote = "";

@ManyToOne
private Strip strip;

public long getId() {
    return key.getId();
}

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


public String getQuote() {
    return quote;
}

public void setQuote(String quote) {
    this.quote = quote;
}

@XmlTransient
public Strip getStrip() {
    return strip;
}

public void setStrip(Strip strip) {
    this.strip = strip;
}

}

还有一种在 Strip 中添加 Quote 的方法：

public JResponse<StripResult> putStripWithQuote(@PathParam("strip_id") long id,                                                     Quote quote) {
    StripResult result = new StripResult();
    EntityManager em = EMFService.get().createEntityManager();
    Strip strip = null;

    try {
        em.getTransaction().begin();

        strip = em.find(Strip.class, id);
        if (strip == null) {
            result.setCode("0");
            result.setMessage("Strip is not found.");
        } else {
            strip.getQuotes().add(quote);
        }

        em.getTransaction().commit();
    } catch (Exception e) {
        result.setCode("0");
        result.setMessage("Exception: " + e.getMessage());
    } finally {
        if (em.getTransaction().isActive()) {
            em.getTransaction().rollback();
        }
        em.close();
    }

    result.setStrip(strip);
    return JResponse.ok(result).build();
}

执行此方法后，我可以在 Datastore Viewer 中看到我已经更新了现有的 Strip 实体和新的 Quote 实体。

即使我查询所有报价一切正常，我也能看到所有报价。

Query q = em.createQuery("select from " + Quote.class.getName());
list = new ArrayList<Quote>(q.getResultList());

m我的问题：entityManager.find(Quote.class, "id of existing quote")不返回任何东西。

我在这里做错了什么或错过了什么？持久性上下文有问题吗？

4

2 回答 2

0

尝试这个

  • 按键查询

TypedQuery<Strip> query = em.createQuery("SELECT s FROM Strips WHERE s.key = ?1",Strip.class); strip = query.setParameter(1, key).getSingleResult();

  • 按ID查询

TypedQuery<Strip> query = em.createQuery("SELECT s FROM Strips WHERE s.id=?1",Strip.class); strip = query.setParameter(1, id).getSingleResult();

  • 查询父条拥有的所有报价

TypedQuery<Strip>query=em.createQuery("SELECT s FROM Strips WHERE s.Strip=1",Strip.class); List<Strip> strip = query.getResultList();

  • 查询数据库中的所有 QOUTES

Query query = em.createQuery("SELECT s FROM Quote s, Quote.class"); List<Quote> ALLQuotes= query.getResultList();

于 2014-02-24T08:13:02.833 回答
0

在您的Quote实体中，定义的主键@Id是key变量，而不是id变量。是您在您的

em.find(Quote.class,"key of existing quote");

?

于 2012-08-23T16:32:52.080 回答