Hibernate 中若是直接使用sql
Session.update(Object o);session
會把這個表中的全部字段更新一遍。spa
好比:.net
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public class TeacherTest {
@Test
public void update(){
Session session = HibernateUitl.getSessionFactory().getCurrentSession();
session.beginTransaction();
Teacher t = (Teacher) session.get(Teacher.class, 3);
t.setName("yangtb2");
session.update(t);
session.getTransaction().commit();
}
}
public class TeacherTest {
@Test
public void update(){
Session session = HibernateUitl.getSessionFactory().getCurrentSession();
session.beginTransaction();
Teacher t = (Teacher) session.get(Teacher.class, 3);
t.setName("yangtb2");
session.update(t);
session.getTransaction().commit();
}
}ip
Hibernate 執行的SQL語句:ci
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Hibernate:
update
Teacher
set
age=?,
birthday=?,
name=?,
title=?
where
id=?
Hibernate:
update
Teacher
set
age=?,
birthday=?,
name=?,
title=?
where
id=?get
咱們只更改了Name屬性,而Hibernate 的sql語句 把全部字段都更改了一次。it
這樣要是咱們有字段是文本類型,這個類型存儲的內容是幾千,幾萬字,這樣效率會很低。io
那麼怎麼只更改咱們更新的字段呢?table
有三中方法:
1.XML中設置property 標籤 update = "false" ,以下:咱們設置 age 這個屬性在更改中不作更改
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<property name="age" update="false"></property>
<property name="age" update="false"></property>
在Annotation中 在屬性GET方法上加上@Column(updatable=false)
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@Column(updatable=false)
public int getAge() {
return age;
}
@Column(updatable=false)
public int getAge() {
return age;
}
咱們在執行 Update方法會發現,age 屬性 不會被更改
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Hibernate:
update
Teacher
set
birthday=?,
name=?,
title=?
where
id=?
Hibernate:
update
Teacher
set
birthday=?,
name=?,
title=?
where
id=?
缺點:不靈活····
2.第2種方法··使用XML中的 dynamic-update="true"
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<class name="com.sccin.entity.Student" table="student" dynamic-update="true">
<class name="com.sccin.entity.Student" table="student" dynamic-update="true">
OK,這樣就不須要在字段上設置了。
但這樣的方法在Annotation中沒有
3.第三種方式:使用HQL語句(靈活,方便)
使用HQL語句修改數據
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public void update(){
Session session = HibernateUitl.getSessionFactory().getCurrentSession();
session.beginTransaction();
Query query = session.createQuery("update Teacher t set t.name = 'yangtianb' where id = 3");
query.executeUpdate();
session.getTransaction().commit();
}
public void update(){
Session session = HibernateUitl.getSessionFactory().getCurrentSession();
session.beginTransaction();
Query query = session.createQuery("update Teacher t set t.name = 'yangtianb' where id = 3");
query.executeUpdate();
session.getTransaction().commit();
}
Hibernate 執行的SQL語句:
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Hibernate:
update
Teacher
set
name='yangtianb'
where
id=3
Hibernate:
update
Teacher
set
name='yangtianb'
where
id=3
這樣就只更新了咱們更新的字段······