java - JPA find() 有效，坚持无异常无结果，删除显示查询并抛出删除分离实例异常

Question

我不知道应该添加什么才能使其正常工作。这是我的实体类:

@Entity
public class Student {

@Id
@GeneratedValue
private int id;
private String name;
private int age;

//setters and getters
}

我的application-context.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd">

<context:annotation-config />
<context:component-scan base-package="orm" />

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="jdbc:mysql://127.0.0.1:3306/test"/>
    <property name="username" value="root"/>
    <property name="password" value="wisla666"/>
</bean>

<bean id="myEmf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
    <property name="dataSource" ref="dataSource" />
    <property name="packagesToScan" value="orm.entity" />
    <property name="jpaVendorAdapter">
        <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
            <property name="showSql" value="true" />
            <property name="generateDdl" value="true" />
            <property name="databasePlatform" value="org.hibernate.dialect.MySQLDialect" />
        </bean>     
    </property> 
</bean>

<bean id="txManager" class="org.springframework.orm.jpa.JpaTransactionManager">
    <property name="entityManagerFactory" ref="myEmf" />
</bean>

<tx:annotation-driven transaction-manager="txManager"/>

这是我的 Dao 类:

import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import org.springframework.stereotype.Repository;
import orm.entity.Student;

@Repository
public class StudentDaoImpl implements StudentDao {

    @PersistenceContext
    private EntityManager entityManager;

    @Override
    public Student loadStudent(int id) {
        return entityManager.find(Student.class, id);
    }

    @Override
    public void saveStudent(Student student) {
        entityManager.persist(student);
    }

    @Override
    public void deleteStudent(Student student) {
        entityManager.remove(entityManager.merge(student));
    }
}

首先，我从数据库加载 Student 对象，它可以工作，然后我尝试从数据库中删除该对象，但它不起作用。在删除期间，sql 语法可见:

Hibernate: select student0_.id as id1_0_0_, student0_.age as age2_0_0_, student0_.name as name3_0_0_ from Student student0_ where student0_.id=?

并且抛出异常:

java.lang.IllegalArgumentException: Removing a detached instance orm.entity.Student#2

在持久化 Student 对象期间，没有任何反应。

问题是我该怎么做才能让它发挥作用？

Answer 1

代码:

@Repository
public class StudentDaoImpl implements StudentDao {

    @PersistenceContext
    private EntityManager entityManager;

    @Transactional
    @Override
    public Student loadStudent(int id) {
        return entityManager.find(Student.class, id);
    }
}

主要方法:

public static void main(String[] args) {
     ApplicationContext context = new ClassPathXmlApplicationContext("application-context.xml");
     StudentServiceImpl ssi = context.getBean("studentServiceImpl", StudentServiceImpl.class);
}

异常:创建名为“studentServiceImpl”的 bean 时出错: Autowiring 依赖项注入(inject)失败

这是我的问题:@Transactional 是否不能与 @PersistenceContext 位于同一位置？为什么我不能分配这个 bean？