Question

摘要：

我正在尝试最小化基于JPA的Java应用程序对数据库进行的查询次数。我指定了@BatchFetch(BatchFetchType.IN)优化提示，但我仍然看到一些我认为多余且不必要的额外查询。

详细信息：

考虑一个简单的域模型：我们有Invoice mgmt系统。发票与订单具有OneToOne关系。我们也有客户，与订单有OneToMany关系。 （客户1＆gt; M订单1＆lt; -1发票）。查找更多details here。找到完整的source code here。这是当前的实体定义：

Client.java（不包括getter和setter ）：

  @Entity(name = "CUSTOMER") 
  public class Customer {
    @Id //signifies the primary key
    @Column(name = "CUST_ID", nullable = false)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long custId;

    @Column(name = "FIRST_NAME", length = 50)
    private String firstName;

    @OneToMany(mappedBy="customer",targetEntity=Order.class,
            fetch=FetchType.LAZY)
    private Collection<Order> orders;
    }

Order.java（不包括getter和setter ）：

 @Entity(name = "ORDERS")
 public class Order {
    @Id
    @Column(name = "ORDER_ID", nullable = false)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long orderId;

    @Column(name = "TOTAL_PRICE", precision = 2)
    private double totPrice;

    @OneToOne(fetch = FetchType.LAZY, optional = false, cascade = CascadeType.ALL,  mappedBy = "order")
    private Invoice invoice;

    @ManyToOne(optional = false)
    @JoinColumn(name = "CUST_ID", referencedColumnName = "CUST_ID")
    private Customer customer;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "ORDER_DETAIL", joinColumns = @JoinColumn(name = "ORDER_ID",    referencedColumnName = "ORDER_ID"), inverseJoinColumns = @JoinColumn(name = "PROD_ID",    referencedColumnName = "PROD_ID"))
    private List<Product> productList;

 }

Invoice.java（不包括getter和setter ）：

@Entity(name = "ORDER_INVOICE")
public class Invoice {

    @Id
    // signifies the primary key
    @Column(name = "INVOICE_ID", nullable = false)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long invoiceId;

    @Column(name = "AMOUNT_DUE", precision = 2)
    private double amountDue;

    @OneToOne(optional = false, fetch = FetchType.LAZY)
    @JoinColumn(name = "ORDER_ID")
    private Order order;

 }

有了这个模型，我运行了一个简单的测试来获取客户的所有订单。

EntityManagerFactory entityManagerFactory =  Persistence.createEntityManagerFactory("testjpa");     
    EntityManager em = entityManagerFactory.createEntityManager();

    Customer customer = em.find(Customer.class, 100L);

    Collection<Order> orders = customer.getOrders();

    for(Order order: orders){
        System.out.println(order.getInvoice().getInvoiceId());
    }

    em.close();

由于所有内容都是延迟获取的，因此我们得到了四个查询，如下所示：

1398882535950|1|1|statement|SELECT CUST_ID, APPT, CITY, EMAIL, FIRST_NAME, LAST_NAME, STREET, LAST_UPDATED_TIME, ZIP_CODE FROM CUSTOMER WHERE (CUST_ID = ?)|SELECT CUST_ID, APPT, CITY, EMAIL, FIRST_NAME, LAST_NAME, STREET, LAST_UPDATED_TIME, ZIP_CODE FROM CUSTOMER WHERE (CUST_ID = 100)

1398882535981|0|1|statement|SELECT ORDER_ID, OREDER_DESC, ORDER_DATE, TOTAL_PRICE, LAST_UPDATED_TIME, CUST_ID FROM ORDERS WHERE (CUST_ID = ?)|SELECT ORDER_ID, OREDER_DESC, ORDER_DATE, TOTAL_PRICE, LAST_UPDATED_TIME, CUST_ID FROM ORDERS WHERE (CUST_ID = 100)

1398882535995|1|1|statement|SELECT INVOICE_ID, AMOUNT_DUE, DATE_CANCELLED, DATE_RAISED, DATE_SETTLED, LAST_UPDATED_TIME, ORDER_ID FROM ORDER_INVOICE WHERE (ORDER_ID = ?)|SELECT INVOICE_ID, AMOUNT_DUE, DATE_CANCELLED, DATE_RAISED, DATE_SETTLED, LAST_UPDATED_TIME, ORDER_ID FROM ORDER_INVOICE WHERE (ORDER_ID = 111)

1398882536004|0|1|statement|SELECT INVOICE_ID, AMOUNT_DUE, DATE_CANCELLED, DATE_RAISED, DATE_SETTLED, LAST_UPDATED_TIME, ORDER_ID FROM ORDER_INVOICE WHERE (ORDER_ID = ?)|SELECT INVOICE_ID, AMOUNT_DUE, DATE_CANCELLED, DATE_RAISED, DATE_SETTLED, LAST_UPDATED_TIME, ORDER_ID FROM ORDER_INVOICE WHERE (ORDER_ID = 222)

由于我不想要N + 1电话来获取发票，我想到使用批量提取并将总查询减少到4（一个查询来获取所有客户订单的发票）。为了做到这一点，我更新了我的Order实体，如下所示：

更新 - Order.java，为Invoice添加BatchFetch。（不包括getter和setter ）：

 @Entity(name = "ORDERS")
 public class Order {
    @Id
    @Column(name = "ORDER_ID", nullable = false)
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long orderId;

    @Column(name = "TOTAL_PRICE", precision = 2)
    private double totPrice;

    @BatchFetch(BatchFetchType.IN)
    @OneToOne(fetch = FetchType.LAZY, optional = false, cascade = CascadeType.ALL,  mappedBy = "order")
    private Invoice invoice;

    @ManyToOne(optional = false)
    @JoinColumn(name = "CUST_ID", referencedColumnName = "CUST_ID")
    private Customer customer;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "ORDER_DETAIL", joinColumns = @JoinColumn(name = "ORDER_ID",    referencedColumnName = "ORDER_ID"), inverseJoinColumns = @JoinColumn(name = "PROD_ID",    referencedColumnName = "PROD_ID"))
    private List<Product> productList;

 }

我再次运行相同的测试，并假设将有3个查询来获取数据。（一个用于客户，一个用于订单，一个用于批量获取发票）。但是，eclipselink 为同一个生成5个查询。以下是查询：

1398883197009|1|1|statement|SELECT CUST_ID, APPT, CITY, EMAIL, FIRST_NAME, LAST_NAME, STREET, LAST_UPDATED_TIME, ZIP_CODE FROM CUSTOMER WHERE (CUST_ID = ?)|SELECT CUST_ID, APPT, CITY, EMAIL, FIRST_NAME, LAST_NAME, STREET, LAST_UPDATED_TIME, ZIP_CODE FROM CUSTOMER WHERE (CUST_ID = 100)

1398883197030|0|1|statement|SELECT ORDER_ID, OREDER_DESC, ORDER_DATE, TOTAL_PRICE, LAST_UPDATED_TIME, CUST_ID FROM ORDERS WHERE (CUST_ID = ?)|SELECT ORDER_ID, OREDER_DESC, ORDER_DATE, TOTAL_PRICE, LAST_UPDATED_TIME, CUST_ID FROM ORDERS WHERE (CUST_ID = 100)

1398883197037|1|1|statement|SELECT INVOICE_ID, AMOUNT_DUE, DATE_CANCELLED, DATE_RAISED, DATE_SETTLED, LAST_UPDATED_TIME, ORDER_ID FROM ORDER_INVOICE WHERE (ORDER_ID IN (?,?))|SELECT INVOICE_ID, AMOUNT_DUE, DATE_CANCELLED, DATE_RAISED, DATE_SETTLED, LAST_UPDATED_TIME, ORDER_ID FROM ORDER_INVOICE WHERE (ORDER_ID IN (111,222))

1398883197042|1|1|statement|SELECT ORDER_ID, OREDER_DESC, ORDER_DATE, TOTAL_PRICE, LAST_UPDATED_TIME, CUST_ID FROM ORDERS WHERE (ORDER_ID = ?)|SELECT ORDER_ID, OREDER_DESC, ORDER_DATE, TOTAL_PRICE, LAST_UPDATED_TIME, CUST_ID FROM ORDERS WHERE (ORDER_ID = 222)

1398883197045|0|1|statement|SELECT INVOICE_ID, AMOUNT_DUE, DATE_CANCELLED, DATE_RAISED, DATE_SETTLED, LAST_UPDATED_TIME, ORDER_ID FROM ORDER_INVOICE WHERE (ORDER_ID = ?)|SELECT INVOICE_ID, AMOUNT_DUE, DATE_CANCELLED, DATE_RAISED, DATE_SETTLED, LAST_UPDATED_TIME, ORDER_ID FROM ORDER_INVOICE WHERE (ORDER_ID = 222)

我不明白为什么要生成最后两个查询。任何帮助来解释发生的事情都会有所帮助。

谢谢！

Answer 1

看起来像是EclipseLink中的一个错误/问题，因为在对象模型中遍历了急切的关系，允许在＆＃34; in＆＃34;中加载第二个Invoice。在引用它的订单加载之前。这会强制Invoice在数据库中查询Order，而不是在缓存中查找。

您可以通过在Invoice to Order关系上使用延迟抓取来解决此问题。此延迟将允许EclipseLink完全构建对象模型，以便在访问时它将位于缓存中。问题中的代码显示此关系标记为Lazy，但这只是JPA提供程序的一个提示，如果不使用代理或字节代码编织而无法在EclipseLink中工作，如下所述： https://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Advanced_JPA_Development/Performance/Weaving https://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Advanced_JPA_Development/Performance/Weaving/Dynamic_Weaving

延迟集合不需要编织，仅适用于1：1和其他优化。

为什么即使使用BatchFetchType.IN提示，JPA / Eclipselink也会激发冗余数据库查询？

1 个答案: