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I am trying to implement Optimistic locking in-order to avoid lost update situation. In my application when two user fetch same record and the first user updates it with some changes. This change is not visible to the second user who view the same record and he makes some changes by himself and updates it. Due to which the first persons change is lost. In-order to prevent this I have written the following but still the issue persist. I am new to this concept, not able to identify the issue.

I have tried to achieve this by reading doc 11.3.4. Customizing automatic versioning section.

  • The configuration file

    <?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="
    http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
    http://www.springframework.org/schema/mvc
    http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd">
    
    <tx:annotation-driven transaction-manager="txManager"/>
    
    <bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
      <property name="dataSource" ref="dataSource"/>
    </bean>
    
    <bean id="hibernateTemplate" class="org.springframework.orm.hibernate3.HibernateTemplate">
      <property name="sessionFactory" ref="sessionFactory"/>
    </bean>
    
    <bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
      <property name="dataSource" ref="dataSource"/>
      <property name="annotatedClasses">
        <list>
            <value>server.bo.Dept</value>
            <value>server.bo.Emp</value>
        </list>
      </property>
      <property name="hibernateProperties">
        <props>
            <prop key="hibernate.dialect">org.hibernate.dialect.SQLServer2008Dialect</prop>
            <prop key="hibernate.show_sql">false</prop>
        </props>
      </property>
    </bean>
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
      <property name="driverClassName" value="net.sourceforge.jtds.jdbc.Driver"/>
      <property name="url" value="${db.url}"/>
      <property name="username" value="${db.username}"/>
      <property name="password" value="${db.password}"/>
    </bean>
    <bean id="deptDAO" class="server.dao.DeptDAOImpl">
      <property name="hibernateTemplate" ref="hibernateTemplate"/>
    </bean>
    </beans>
    
  • Entity Class

    @Entity
    @Table(name = "Dept")
    @org.hibernate.annotations.Entity(dynamicUpdate = true,optimisticLock = OptimisticLockType.ALL)
    public class Dept{
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        @Column(name = "ID")
        Long id;
    
        @OneToMany(cascade = CascadeType.REMOVE, fetch = FetchType.EAGER, mappedBy = "deptId")
        @Fetch(FetchMode.SELECT)
        @OrderBy(value = "id DESC")
        List<Emp> Emplist;
    
        public Dept() {}
        // Getters and setters
    }
    
  • DAO Impl

    public class DeptDAOImpl extends HibernateDaoSupport implements DeptDAO {
        @Transactional(readOnly = true, propagation = Propagation.REQUIRED, isolation = Isolation.REPEATABLE_READ)
        public Dept getDeptById(Long id) {
                Object param[] = new Object[]{id};
                String  query = "select d from Dept d where d.id=? and d.deleted='0'";
                List<Dept> deptDetailsList = getHibernateTemplate().find(query,param);
                Dept deptDetails = null;
                if(deptDetailsList !=null && deptDetailsList .size()>0)
                    deptDetails = (Dept)deptDetailsList.get(0);
                return deptDetails ;
        }
    
        @Transactional(readOnly = false, propagation = Propagation.REQUIRED, isolation = Isolation.REPEATABLE_READ)
        public long updateDept(Dept dept) {
                if (dept.getId() == null) { 
                    getSession().save(dept);
                } else {
                    getSession().update(dept);
                }
                if (dept.getEmplist() != null) {
                        final int size = dept.getEmplist().size();
                        for (int i = size - 1; i >= 0; i--) { 
                            Emp emp = dept.getEmplist().get(i);
                            if (emp.getDeptId() == null) {
                                emp.setDeptId(dept.getId());
                        }
                        if (RecordStatus.NEW.equals(emp.getRecordStatus())) {
                            getSession().save(emp);
                        } else if (RecordStatus.DELETED.equals(emp.getRecordStatus())) {
                            getSession().delete(emp);
                        } else if (RecordStatus.MODIFIED.equals(emp.getRecordStatus())) {
                            getSession().update(emp);
                        }
                    }
            }
            return dept.getId();
        }
    }
    

Thanks in advance

4

1 回答 1

13

JPA/Hibernate Optmistic 锁定通过使用某个字段来存储最后修改的版本(例如时间戳、长),然后将会话中实体的版本与数据库中的实体进行比较,以查看是否可以保存更改。

为此,您需要在实体中使用@Version 注释的字段。

请参阅下面的示例。

http://www.javacodegeeks.com/2012/11/jpahibernate-version-based-optimistic-concurrency-control.html

为了在 Web 应用程序中工作需要进一步考虑,但是如果两个人加载相同的实体进行编辑,然后一段时间后提交他们的编辑,他们很可能都会成功,除非您使用某种长时间运行的会话,否则实体正在编辑的将在表单提交时从数据库中重新加载、填充和保存。

例如修订版 1 中的实体

  • 用户 1 加载进行编辑:修订为 1
  • 用户 2 加载进行编辑:修订为 1
  • 用户 2 提交表单:加载实体(在 r1),绑定字段,保存实体:修订版为 2。
  • 用户 1 提交表单:实体(在 r2)已加载,字段已绑定,实体已保存:修订版为 3。

因此,要使其正常工作,您可以查看使用表单提交隐藏字段,该表单在加载时存储实体修订。因此,在上面的最后一步,当用户 1 提交时,修订字段将被设置回 1,并且更新将失败,因为数据库中的记录为 r2。

于 2013-10-18T18:39:15.953 回答