EntityManager.find() 找不到实体

Question

我在使用 JPA 和 Hibernate 时遇到问题，其中 EntityManager.find() 甚至 EntityManager.createQuery() 不会在我的数据库中返回具有相应 ID 的实体。前者返回null，后者抛出No entity found for query 异常。我知道具有该 ID 的实体存在于数据库中，因为我在运行代码时盯着条目。

我采取了几个步骤来到达失败的地方。首先，我将两个项目添加到我的 DayItem 表并将它们返回给客户端。我在客户端更改它们的值并使用 POST 将它们发送回服务器。一旦被服务器接收到，我创建一个新的EntityManager 并尝试通过获取实体的类和 ID 并将这些值传递给EntityManager.find(Class, ID) 来按 ID 删除实体。

这会在数据库中找到具有原始值的实体，而不是从客户端发送过来的已更改的实体。 EntityManager.find(Class, ID) 也正是问题所在。找到数据库中的实体后，我会在实体上调用EntityManager.remove() 将其删除。

我没有在服务器接收到实体时直接在实体上使用EntityManager.merge() 的原因是它们的唯一键已交换，除非我在运行之前将它们从数据库中删除，否则这将导致违反约束EntityManager.merge().

最后，从数据库中删除实体后，我通过在它们上调用 EntityManager.merge() 将它们添加回更新值。

请看我下面的代码，任何关于为什么 EntityManager.find() 返回 null 以及为什么查询抛出 No entity found for query 异常的帮助都会有很大帮助。

这是 DayItem 表上的唯一键：

ALTER TABLE DAY_ITEM
ADD CONSTRAINT DAY_ITEM_UK
UNIQUE (EMAIL, MOD_ID, FM_ORDER, DAYS_DATE);

这里是 DayItem 表实体：

@Entity
@Table(name = "DAY_ITEM")
public class DayItem implements GtEntity, Serializable{
    private Long id;
    private String email;
    private String name;
    private BigDecimal amount;
    private Integer modId;
    private Integer fmOrder;
    private String modName;
    private Date daysDate;
    private String daysDateString;
    private Long foodId;
    private Long mealId;
    private FoodItem foodItem;
    private MealItem mealItem;
    private ArrayList<FoodItem> foodItems;
    private ArrayList<MealItem> mealItems;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Long getId() {
        return id;
    }

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

    @Basic
    @Column(name = "EMAIL", nullable = false, length = 50)
    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Basic
    @Column(name = "NAME", nullable = true, length = 100)
    public String getName() {
        return name;
    }

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

    @Basic
    @Column(name = "AMOUNT", nullable = true)
    public BigDecimal getAmount() {
        return amount;
    }

    public void setAmount(BigDecimal amount) {
        this.amount = amount;
    }

    @Basic
    @Column(name = "MOD_ID", nullable = false)
    public Integer getModId() {
        return modId;
    }

    public void setModId(Integer modId) {
        this.modId = modId;
    }

    @Basic
    @Column(name = "FM_ORDER", nullable = false)
    public Integer getFmOrder() {
        return fmOrder;
    }

    public void setFmOrder(Integer fmOrder) {
        this.fmOrder = fmOrder;
    }

    @Basic
    @Column(name = "MOD_NAME", nullable = true, length = 50)
    public String getModName() {
        return modName;
    }

    public void setModName(String modName) {
        this.modName = modName;
    }

    @Basic
    @Column(name = "DAYS_DATE", nullable = false)
    public Date getDaysDate() {
        return daysDate;
    }

    public void setDaysDate(Date daysDate) {
        this.daysDate = daysDate;
    }

    @Transient
    public String getDaysDateString() {
        return daysDateString;
    }

    public void setDaysDateString(String daysDateString) {
        this.daysDateString = daysDateString;
    }

    @Basic
    @Column(name = "FOOD_ID", nullable = true)
    public Long getFoodId() {
        return foodId;
    }

    public void setFoodId(Long foodId) {
        this.foodId = foodId;
    }

    @Basic
    @Column(name = "MEAL_ID", nullable = true)
    public Long getMealId() {
        return mealId;
    }

    public void setMealId(Long mealId) {
        this.mealId = mealId;
    }

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "FOOD_ID", referencedColumnName = "ID",
            updatable = false, insertable = false)
    public FoodItem getFoodItem() {
        return foodItem;
    }

    public void setFoodItem(FoodItem foodItem) {
        this.foodItem = foodItem;
    }

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "MEAL_ID", referencedColumnName = "ID",
            updatable = false, insertable = false)
    public MealItem getMealItem() {
        return mealItem;
    }

    public void setMealItem(MealItem mealItem) {
        this.mealItem = mealItem;
    }

    @Transient
    public ArrayList<FoodItem> getFoodItems() {
        return foodItems;
    }

    public void setFoodItems(ArrayList<FoodItem> foodItems) {
        this.foodItems = foodItems;
    }

    @Transient
    public ArrayList<MealItem> getMealItems() {
        return mealItems;
    }

    public void setMealItems(ArrayList<MealItem> mealItems) {
        this.mealItems = mealItems;
    }

    public void makeDaysDate() throws ParseException{
        DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
        this.daysDate = new Date(formatter.parse(this.daysDateString).getTime());
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof DayItem)) return false;

        DayItem dayItem = (DayItem) o;

        if (!getEmail().equals(dayItem.getEmail())) return false;
        if (!getModId().equals(dayItem.getModId())) return false;
        if (!getFmOrder().equals(dayItem.getFmOrder())) return false;
        return getDaysDate().equals(dayItem.getDaysDate());

    }

    @Override
    public int hashCode() {
        int result = getEmail().hashCode();
        result = 31 * result + getModId().hashCode();
        result = 31 * result + getFmOrder().hashCode();
        result = 31 * result + getDaysDate().hashCode();
        return result;
    }
}

这是添加 DayItem 的代码：

@Override
public List<DayItem> saveDayItem(DayItem item) throws Exception {
    List<DayItem> results = null;
    EntityManager manager = createEntityManager();
    EntityTransaction tx = manager.getTransaction();
    try {
        tx.begin();
        DayItem managedItem = manager.merge(item);
        manager.flush();
        manager.clear();
        tx.commit();
        results = findUserDay(managedItem.getDaysDate(), managedItem.getEmail(), manager);
    } catch (RuntimeException e) {
        tx.rollback();
        throw e;
    } finally {
        manager.close();
    }
    return results;
}

这是删除 DayItems 的代码：

public <T extends GtEntity> void batchDelete(List<T> entities) throws Exception {
    if (!entities.isEmpty()) {
        EntityManager manager = createEntityManager();
        EntityTransaction tx = manager.getTransaction();
        try {
            tx.begin();
            for (int i = 0; i < entities.size(); i++) {
                if (i % this.jdbcBatchSize == 0) {
                    manager.flush();
                    manager.clear();
                }

                T del = entities.get(i);
                T managed = manager.find((Class<T>)del.getClass(), del.getId());
                //The line above is where the problem happens

                manager.remove(managed);
            }
            manager.flush();
            manager.clear();
            tx.commit();
        } catch (RuntimeException e) {
            tx.rollback();
            throw e;
        }
    }
}

Answer 1

    public Clan saveClan(String ime, String prezime, String adresa, Date datumRodjenja, Date datumUpisa,
                int idKategorije) {
            try {
                EntityManager em = JPAUtil.getEntityManager();
                em.getTransaction().begin();
    
                Kategorija k = em.find(Kategorija.class, idKategorije);
                Clan c = new Clan();
                c.setIme(ime);
                c.setPrezime(prezime);
                c.setAdresa(adresa);
                c.setDatumRodjenja(datumRodjenja);
                c.setDatumUpisa(datumUpisa);
                c.setKategorija(k);
                em.persist(c);
    
                em.getTransaction().commit();
                return c;
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }
        }

public boolean razduzi(int id) {
        try {
            EntityManager em = JPAUtil.getEntityManager();
            em.getTransaction().begin();

            Zaduzenje z = em.find(Zaduzenje.class, id);
            z.setDatumVracanja(new Date());
            em.merge(z);

            em.getTransaction().commit();
            return true;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

Answer 2

    public boolean deleteClan(Integer clBroj) {
            try {
                EntityManager em = JPAUtil.getEntityManager();
                em.getTransaction().begin();
    
                Clan c = em.find(Clan.class, clBroj);
    
                List<Zaduzenje> zaduzenjaClana = em
                        .createQuery("" + "select z from Zaduzenje z where " + "z.clan.clanskibroj=:br", Zaduzenje.class)
                        .setParameter("br", clBroj).getResultList();
    
                for (Zaduzenje z : zaduzenjaClana) {
                    em.remove(z);
                }
                em.remove(c);
                em.getTransaction().commit();
                return true;
            } catch (Exception e) {
                e.printStackTrace();
                return false;
            }
        }

public List<Integer> dodajPrimerke(int idKnjige, int brojPrimeraka) {
        ArrayList<Integer> invBrojevi = new ArrayList<Integer>();
        try {
            EntityManager em = JPAUtil.getEntityManager();
            Knjiga k = em.find(Knjiga.class, idKnjige);
            if (k != null) {
                em.getTransaction().begin();
                for (int i = 0; i < brojPrimeraka; i++) {
                    Primerak p = new Primerak();
                    p.setKnjiga(k);
                    em.persist(p);
                    invBrojevi.add(p.getInvBroj());
                }
                em.getTransaction().commit();
            }
            return invBrojevi;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

Answer 3

公共列表 getUlogeZaPredstavu(int idPredstave){ EntityManager em = JPAUtil.getEntityManager();

    List<Glumi> uloge = em.createQuery("select g from Glumi g where "
            + "g.uloga.predstava.idPredstava = :paramIdPredstava", Glumi.class)
            .setParameter("paramIdPredstava", idPredstave).getResultList();
    return uloge;
}

public Zanr getZanr(int id) {
    EntityManager em = JPAUtil.getEntityManager();
    Zanr z = em.find(Zanr.class, id);
    return z;
}