Question

Student.java

package Model;


import java.util.Set;

public class Student {
private int studentID;
private  String name;
private String city;
private Set<Address> AddressList;
private Set<Contact> ContactList;

public Set<Contact> getContactList() {
    return ContactList;
}

public void setContactList(Set<Contact> contactList) {
    ContactList = contactList;
}

public Set<Address> getAddressList() {
    return AddressList;
}

public void setAddressList(Set<Address> addressList) {
    AddressList = addressList;
}

public int getStudentID() {
    return studentID;
}

public void setStudentID(int studentID) {
    this.studentID = studentID;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getCity() {
    return city;
}

public void setCity(String city) {
    this.city = city;
}

}

Address.java

package Model;

public class Address {

private int Aid;
private String fullAddress;
//private Student student;
/*public Student getStudent() {
    return student;
}
public void setStudent(Student student) {
    this.student = student;
}*/
public int getAid() {
    return Aid;
}
public void setAid(int aid) {
    Aid = aid;
}
public String getFullAddress() {
    return fullAddress;
}
public void setFullAddress(String fullAddress) {
    this.fullAddress = fullAddress;
}
}

Contact.java

package Model;

public class Contact {
private int contactId;
private String mobileNo;

public int getContactId() {
    return contactId;
}
public void setContactId(int contactId) {
    this.contactId = contactId;
}
public String getMobileNo() {
    return mobileNo;
}
public void setMobileNo(String mobileNo) {
    this.mobileNo = mobileNo;
}



 }

Student.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Model.Student" table="Student">
    <id name="studentID" type="int">
        <column name="StudentID" />
        <generator class="identity" />
    </id>
    <property name="name" type="java.lang.String"/>
    <property name="city" type="java.lang.String"/>
    <set name="AddressList">
        <key column="studentID"/>
        <one-to-many class="Model.Address"/>        
    </set>
    <set name="ContactList">
        <key column="studentID"/>
        <one-to-many class="Model.Contact"/>        
    </set>
</class>

Address.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Model.Address" table="Address">
    <id name="Aid" type="int">
        <column name="Aid" />
        <generator class="identity" />
    </id>
    <property name="fullAddress" type="java.lang.String"/>
</class>

Contact.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="Model.Contact" table="Contact">
    <id name="contactId" type="int">
        <column name="contactId" />
        <generator class="identity" />
    </id>
    <property name="mobileNo" type="java.lang.String"/>
</class>

主要方法。

public static void main(String[] args)
{
    Configuration cfg=new Configuration();
    cfg.configure("hibernate.cfg.xml");
    SchemaExport se=new SchemaExport(cfg);
    se.setOutputFile("D:\\abc.sql");
    se.create(true,true);//create(boolean script, boolean export) 

    System.out.println("------------------Saving of Student--------------------");
    Student student =new Student();
    student.setName("Yograj");
    student.setCity("Nanded");
    Set<Address> addressList=new HashSet<Address>();
    Address address=new Address();
    address.setFullAddress("Chikhali Nanded");
    addressList.add(address);
    address=null;
    address=new Address();
    address.setFullAddress("karvenagar Pune");
    addressList.add(address);
    student.setAddressList(addressList);

    Set<Contact> contactList=new HashSet<Contact>();
    Contact contact=new Contact();
    contact.setMobileNo("9403330577");
    contactList.add(contact);
    contact=null;
    contact=new Contact();
    contact.setMobileNo("9890864805");
    contactList.add(contact);
    student.setContactList(contactList);

    boolean result=new StudentServices().SaveStudent(student);

    if(result)
    {
        System.out.println("------------------Save Student succ..--------------------");
    }
    else
    {
        System.out.println("------------------Saving failed--------------------");
    }

    System.out.println("------------------Student Details--------------------");
    List<Student> studentList=new StudentServices().GetStudentlist();
    for (Student stud : studentList) {
        System.out.println("Name:"+stud.getName());
        System.out.println("City:"+stud.getCity());
        for (Address add : stud.getAddressList()) {
            System.out.println("Full Address:"+add.getFullAddress());
        }
        for (Contact cont : stud.getContactList()) {
            System.out.println("Full Address:"+cont.getMobileNo());
        }
    }
    System.out.println("Execution over.");


}

StudentService.Java

package Service;

import java.util.List;

import javassist.runtime.Inner;

import org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Restrictions;
import org.hibernate.sql.JoinType;

import Model.Address;
import Model.Contact;
import Model.Student;

public class StudentServices {
public boolean SaveStudent(Student student) {
    try {
        Configuration cfg = new Configuration().configure();
        SessionFactory sf = cfg.buildSessionFactory();
        Session session = sf.openSession();
        Transaction transaction = session.beginTransaction();

        session.save(student);
        for (Address add : student.getAddressList()) {
            session.save(add);

        }
        for (Contact cont : student.getContactList()) {
            session.save(cont);

        }
        transaction.commit();
        session.close();
        return true;
    } catch (HibernateException e) {
        return false;
    }
}

public List<Student> GetStudentlist() {
    try {
        Configuration cfg = new Configuration().configure();
        SessionFactory sf = cfg.buildSessionFactory();
        Session session = sf.openSession();
        Transaction transaction = session.beginTransaction();
        Criteria criteria = session.createCriteria(Student.class, "Student")
                .createAlias("Student.AddressList", "Address",JoinType.INNER_JOIN)
                .createAlias("Student.ContactList", "Contact",JoinType.INNER_JOIN);
        List<Student> studentList = criteria.list();

        transaction.commit();
        session.close();
        return studentList;
    } catch (HibernateException e) {
        return null;
    }
}
}

当我执行main方法时，hibernate将创建数据库和table.in所有表，它将存储记录，但是当我使用条件API获取记录时，它会给出错误“org.hibernate.LazyInitializationException。”

Answer 1

在您的情况下student.addressList和student.contactList使用延迟加载。延迟加载意味着，值不会与studentList一起加载，但只有当您使用getAddressList()和getContactList访问它们时才会加载。

只有会话仍处于打开状态时，延迟加载才有效。如果在关闭会话后仍未访问已加载的组件，则会抛出LazyInitializationException，如示例所示。

你在做的是：

：打开会话
：加载所有学生
：关闭会话
in main：for each students
in main：通过student.getAddressList()

这会在步骤5中引发异常，因为您访问了适用于延迟加载的地址列表，并且无法再加载数据，因为会话已在步骤3中关闭。

您必须在致电getAddressList()和getContactList()后关闭会话，然后才能运作。

顺便说一句，当您只读取GetStudentlist中的数据时，您不需要开始事务，也不需要提交任何内容。

Answer 2

尝试访问学生中的方法以初始化代理。

尝试在服务方法中调用student.getAddress（）。getFullAddress（）以初始化代理。

这样，您将避免延迟初始化异常。

另一种方法是将渴望提取设置为true，但我宁愿先使用第一种方法。

Answer 3

对于Junit测试用例，您需要将打开的Session绑定到当前的Thread。

@media screen and (max-width: 900px) {
  .my_element:hover {
    opacity: none:
  }
}

如果你想不再关心LazyInitialisationException，请阅读this，它会很好地解释会发生什么，以及如何解决问题

org.hibernate.LazyInitializationException

3 个答案: