JPA为我没有访问的相关实体运行数百个选择
JPA为我没有访问的相关实体运行数百个选择
提问于 2013-10-11 14:43:43
我正在学习JPA，并试图编写一个小应用程序来显示带有约会的表。
现在，我只是使用h:dataTable (JSF)显示了对约会的描述，但出于某种原因，这会导致JPA为每个约会生成一个选择，以检索相关的Creator实体。因此，例如，如果我有100个约会，这将生成101个对数据库的查询(一个用于检索约会，另一个用于每个创建者)，即使我没有以任何方式访问这个Creator实体。
这是我的Appointment实体。它通过一个不是主键的代码引用Creator实体，但我不能更改表的结构。
@Entity
public class Appointment implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private BigDecimal id;
private String description;
private Timestamp date;
@ManyToOne
@JoinColumn(name = "APPOINTMENT_CREATOR", referencedColumnName = "USER_CODE")
private Creator creator;
// Getters and setters
}这是Creator实体
@Entity
public class Creator implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private BigDecimal id;
private String name;
private String surname;
@Column(name="USER_CODE")
private int userCode;
@OneToMany(mappedBy = "creator")
private List<Cita> appointments;
public Appointment addAppointment(Appointment appointment) {
getAppointments().add(appointment);
appointment.setCreator(this);
return appointment;
}
public Appointment removeAppointment(Appointment appointment) {
getAppointments().remove(appointment);
appointment.setCreator(null);
return appointment;
}
// Getters and setters
}这是我的刀
@Repository
public class AppointmentDAO {
private EntityManager entityManager;
@PersistenceContext
public void setEntityManager(EntityManager em) {
this.entityManager = em;
}
public List<Appointment> findAll() {
List<Appointment> result = null;
try {
result = this.entityManager.createQuery("SELECT a from Appointment a").getResultList();
} catch (Exception ex) {
}
return result;
}
}这是我的日志摘录
[EL Finest]: connection: 2013-10-11 16:22:35.406--ServerSession(33459456)--Connection(11062282)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Connection released to connection pool [read].
[EL Finest]: query: 2013-10-11 16:22:35.421--ServerSession(33459456)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Execute query ReadObjectQuery(name="creator" referenceClass=Creator sql="SELECT ID, SURNAME, USER_CODE, NAME FROM CREATOR WHERE (USER_CODE = ?)")
[EL Finest]: connection: 2013-10-11 16:22:35.421--ServerSession(33459456)--Connection(20248250)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Connection acquired from connection pool [read].
[EL Finest]: connection: 2013-10-11 16:22:35.421--ServerSession(33459456)--Thread(Thread["http-bio-8080"-exec-3,5,main]) --reconnecting to external connection pool
[EL Fine]: sql: 2013-10-11 16:22:35.453--ServerSession(33459456)--Connection(3304058)--Thread(Thread["http-bio-8080"-exec-3,5,main])--SELECT ID, SURNAME, USER_CODE, NAME FROM CREATOR WHERE (USER_CODE = ?)
bind => [7054382]
[EL Finest]: connection: 2013-10-11 16:22:35.515--ServerSession(33459456)--Connection(20248250)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Connection released to connection pool [read].
[EL Finest]: transaction: 2013-10-11 16:22:35.531--UnitOfWork(12558692)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Register the existing object net.turbo.model.entities.Creator@b2e368
[EL Finest]: query: 2013-10-11 16:22:35.531--ServerSession(33459456)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Execute query ReadObjectQuery(name="creator" referenceClass=Creator sql="SELECT ID, SURNAME, USER_CODE, NAME FROM CREATOR WHERE (USER_CODE = ?)")
[EL Finest]: connection: 2013-10-11 16:22:35.531--ServerSession(33459456)--Connection(32578948)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Connection acquired from connection pool [read].
[EL Finest]: connection: 2013-10-11 16:22:35.531--ServerSession(33459456)--Thread(Thread["http-bio-8080"-exec-3,5,main])--reconnecting to external connection pool
[EL Fine]: sql: 2013-10-11 16:22:35.562--ServerSession(33459456)--Connection(13173146)--Thread(Thread["http-bio-8080"-exec-3,5,main])--SELECT ID, SURNAME, USER_CODE, NAME FROM CREATOR WHERE (USER_CODE = ?)
bind => [7042199]
[EL Finest]: connection: 2013-10-11 16:22:35.64--ServerSession(33459456)--Connection(32578948)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Connection released to connection pool [read].
[EL Finest]: transaction: 2013-10-11 16:22:35.64--UnitOfWork(12558692)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Register the existing object net.turbo.model.entities.Creator@1b0c903
[EL Finest]: query: 2013-10-11 16:22:35.64--ServerSession(33459456)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Execute query ReadObjectQuery(name="creator" referenceClass=Creator sql="SELECT ID, SURNAME, USER_CODE, NAME FROM CREATOR WHERE (USER_CODE = ?)")
[EL Finest]: connection: 2013-10-11 16:22:35.64--ServerSession(33459456)--Connection(7112313)--Thread(Thread["http-bio-8080"-exec-3,5,main])--Connection acquired from connection pool [read].
[EL Finest]: connection: 2013-10-11 16:22:35.64--ServerSession(33459456)--Thread(Thread["http-bio-8080"-exec-3,5,main])--reconnecting to external connection pool
[EL Fine]: sql: 2013-10-11 16:22:35.671--ServerSession(33459456)--Connection(15764427)--Thread(Thread["http-bio-8080"-exec-3,5,main])--SELECT ID, SURNAME, USER_CODE, NAME FROM CREATOR WHERE (USER_CODE = ?)
bind => [7076961]
..........
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..........回答 2
Stack Overflow用户
回答已采纳
发布于 2013-10-15 07:44:03
好吧，我解决了。这是因为我使用的是Tomcat，而EclipseLink无法使用织入来更改类，而没有这种情况，EclipseLink只能使用急切的加载。
我刚从Tomcat转移到一个真正的应用服务器。
Stack Overflow用户
发布于 2013-10-11 14:51:29
fetchType关系的默认ManyToOne是EAGER。将其设置为LAZY，这将导致在访问之前不会查询Creator实体。
@ManyToOne(fetch=FetchType.LAZY)
@JoinColumn(name = "APPOINTMENT_CREATOR", referencedColumnName = "USER_CODE")
private Creator creator;页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/19320994
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