【发布时间】：2014-11-07 09:06:16
【问题描述】：
在下面的代码中，我预计会发生n+1 查询问题，但它没有发生。
User.java：
import java.util.*;
public class User {
private long userId;
private String firstName;
private Set phones;
public User() {
System.out.println("0-arg constructor :User");
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public long getUserId() {
return userId;
}
public void setUserId(long userId) {
this.userId = userId;
}
public Set getPhones() {
return phones;
}
public void setPhones(Set phones) {
this.phones = phones;
}
}
PhoneNumber.java：
public class PhoneNumber {
private String numberType;
private long phone;
private long id;
User parent;
public PhoneNumber() {
System.out.println("0-arg constructor :PhoneNumber");
}
// write getXxx(),setXxx() methods (4 sets)
public void setId(long id) {
this.id = id;
}
public long getId() {
return id;
}
public String getNumberType() {
return numberType;
}
public void setNumberType(String numberType) {
this.numberType = numberType;
}
public long getPhone() {
return phone;
}
public void setPhone(long phone) {
this.phone = phone;
}
public void setParent(User parent) {
this.parent = parent;
}
public User getParent() {
return parent;
}
}
User.hbm.xml：
<hibernate-mapping>
<class name="User"
table="USER_TABLE" >
<id name="userId"
column="USER_ID"/>
<property name="firstName"
column="FIRST_NAME"/>
<set name="phones"
table="PHONE_NUMBERS" cascade="all"
lazy="true">
<key column="UNID"/>
<one-to-many
class="PhoneNumber"/>
</set>
</class>
</hibernate-mapping>
phoneNumber.hbm：
<hibernate-mapping>
<class name="PhoneNumber" table="PHONE_NUMBERS" >
<id name="phone" column="PHONE"/>
<property name="numberType" column="NUMBER_TYPE"/>
<property name="id" column="UNID" insert="false" update="false"/>
<many-to-one name="parent" class="User" column="UNID2" cascade="all"/>
</class>
</hibernate-mapping>
hibernate.cfg：
<session-factory>
<property
name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</
property>
<property
name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:xe</prope
rty>
<property
name="hibernate.connection.username">system</property>
<property
name="hibernate.connection.password">oracle123</property>
<property
name="hibernate.dialect">org.hibernate.dialect.OracleDialect</property>
<property name="hibernate.hbm2ddl.auto">update</property>
<property name="show_sql">true</property>
<mapping resource="user.hbm.xml"/>
<mapping resource="phoneNumber.hbm.xml"/>
</session-factory>
HQLClient.java：
import org.hibernate.*;
import org.hibernate.cfg.*;
import java.util.*;
public class HQLJoinsClient {
public static void main(String[] args) {
try {
Configuration conf = new Configuration().configure();
SessionFactory factory = conf.buildSessionFactory();
Session ses = factory.openSession();
String hql = "from User ";
Query q = ses.createQuery(hql);
List l = q.list();
System.out.println("++++++++++++++++++" + l.size()
+ "+++++++++++++");
for (int i = 0; i < l.size(); ++i) {
User u1 = (User) l.get(i);
System.out
.println("\n\n\nParent----------------------------------------------------------------->");
System.out.print("user id: " + u1.getUserId());
System.out.println("FirstName " + u1.getFirstName());
Set s = u1.getPhones();
if (s != null) {
Iterator it = s.iterator();
while (it.hasNext()) {
PhoneNumber p1 = (PhoneNumber) it.next();
System.out.println("\nchild---->");
System.out.print("Number Type=" + p1.getNumberType());
System.out.print("Phone Number=" + p1.getPhone());
System.out.println("User id=" + p1.getId());
}// inner while
}// if
}
ses.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
输出为：
INFO: schema update complete Hibernate: select user0_.USER_ID as USER1_0_, user0_.FIRST_NAME as FIRST2_0_ from USER_TABLE user0_
0-arg constructor :User 0-arg constructor :User 0-arg constructor :User ++++++++++++++++++3+++++++++++++++++++++++++ Parent-----------------------------------------------------------------> user id: 102FirstName ravi Hibernate: select phones0_.UNID as UNID1_, phones0_.PHONE as PHONE1_, phones0_.PHONE as PHONE1_0_, phones0_.NUMBER_TYPE as NUMBER2_1_0_, phones0_.UNID as UNID1_0_, phones0_.UNID2 as UNID4_1_0_ from PHONE_NUMBERS phones0_ where phones0_.UNID=? 0-arg constructor :PhoneNumber 0-arg constructor :PhoneNumber 0-arg constructor :PhoneNumber child----> Number Type=resPhone Number=81818181User id=102 child----> Number Type=officePhone Number=71717171User id=102 child----> Number Type=homePhone Number=91919191User id=102 Parent-----------------------------------------------------------------> user id: 103FirstName jayendra Hibernate: select phones0_.UNID as UNID1_, phones0_.PHONE as PHONE1_, phones0_.PHONE as PHONE1_0_, phones0_.NUMBER_TYPE as NUMBER2_1_0_, phones0_.UNID as UNID1_0_, phones0_.UNID2 as UNID4_1_0_ from PHONE_NUMBERS phones0_ where phones0_.UNID=? 0-arg constructor :PhoneNumber 0-arg constructor :PhoneNumber child----> Number Type=resPhone Number=3748329382User id=103 child----> Number Type=homePhone Number=538432342User id=103 Parent-----------------------------------------------------------------> user id: 104FirstName mike Hibernate: select phones0_.UNID as UNID1_, phones0_.PHONE as PHONE1_, phones0_.PHONE as PHONE1_0_, phones0_.NUMBER_TYPE as NUMBER2_1_0_, phones0_.UNID as UNID1_0_, phones0_.UNID2 as UNID4_1_0_ from PHONE_NUMBERS phones0_ where phones0_.UNID=? 0-arg constructor :PhoneNumber 0-arg constructor :PhoneNumber child----> Number Type=homePhone Number=238349384User id=104 child----> Number Type=mobilePhone Number=9455682832User id=104
我希望每个电话号码记录到一个用户 ID 会有单独的选择语句，但对于 3 个电话号码 - 1 个用户 ID 有一个选择语句 [而不是 (3+1)]。为什么会这样？
谢谢！
【问题讨论】：
标签： hibernate hibernate-onetomany select-n-plus-1