1. Abfragetypen
1.oid query-get
2. Objektattribut-Navigationsabfrage
3.HQL
4.Kriterien
5. Native SQL
2. Abfrage-HQL-Syntax
//学习HQL语法public class Demo { //基本语法 @Testpublic void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql = " from cn.itcast.domain.Customer ";//完整写法String hql2 = " from Customer "; //简单写法String hql3 = " from java.lang.Object ";
Query query = session.createQuery(hql3);
List list = query.list();
System.out.println(list);//---------------------------------------------------- tx.commit();
session.close();
}
@Test//排序public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql1 = " from cn.itcast.domain.Customer order by cust_id asc ";//完整写法String hql2 = " from cn.itcast.domain.Customer order by cust_id desc ";//完整写法
Query query = session.createQuery(hql2);
List list = query.list();
System.out.println(list);//---------------------------------------------------- tx.commit();
session.close();
}
@Test//条件查询public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql1 = " from cn.itcast.domain.Customer where cust_id =? ";//完整写法String hql2 = " from cn.itcast.domain.Customer where cust_id = :id ";//完整写法
Query query = session.createQuery(hql2);
// query.setParameter(0, 2l);query.setParameter("id", 2l);
List list = query.list();
System.out.println(list);//---------------------------------------------------- tx.commit();
session.close();
}
@Test//分页查询public void fun4(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql1 = " from cn.itcast.domain.Customer ";//完整写法
Query query = session.createQuery(hql1); //limit ?,?// (当前页数-1)*每页条数query.setFirstResult(2);
query.setMaxResults(2);
List list = query.list();
System.out.println(list);//---------------------------------------------------- tx.commit();
session.close();
}
@Test//统计查询//count 计数//sum 求和//avg 平均数//max//minpublic void fun5(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql1 = " select count(*) from cn.itcast.domain.Customer ";//完整写法String hql2 = " select sum(cust_id) from cn.itcast.domain.Customer ";//完整写法String hql3 = " select avg(cust_id) from cn.itcast.domain.Customer ";//完整写法String hql4 = " select max(cust_id) from cn.itcast.domain.Customer ";//完整写法String hql5 = " select min(cust_id) from cn.itcast.domain.Customer ";//完整写法
Query query = session.createQuery(hql5);
Number number = (Number) query.uniqueResult();
System.out.println(number);//---------------------------------------------------- tx.commit();
session.close();
}
@Test//投影查询public void fun6(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql1 = " select cust_name from cn.itcast.domain.Customer ";
String hql2 = " select cust_name,cust_id from cn.itcast.domain.Customer ";
String hql3 = " select new Customer(cust_id,cust_name) from cn.itcast.domain.Customer ";
Query query = session.createQuery(hql3);
List list = query.list();
System.out.println(list); //---------------------------------------------------- tx.commit();
session.close();
}
}HQL-Syntax lernen
public class Demo2 {//回顾-原生SQL// 交叉连接-笛卡尔积(避免)// select * from A,B // 内连接// |-隐式内连接// select * from A,B where b.aid = a.id// |-显式内连接// select * from A inner join B on b.aid = a.id// 外连接// |- 左外// select * from A left [outer] join B on b.aid = a.id// |- 右外// select * from A right [outer] join B on b.aid = a.id//---------------------------------------------------------------------//HQL的多表查询//内连接(迫切)//外连接// |-左外(迫切)// |-右外(迫切)
@Test//HQL 内连接 => 将连接的两端对象分别返回.放到数组中.public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql = " from Customer c inner join c.linkMens ";
Query query = session.createQuery(hql);
List<Object[]> list = query.list(); for(Object[] arr : list){
System.out.println(Arrays.toString(arr));
}//---------------------------------------------------- tx.commit();
session.close();
}
@Test//HQL 迫切内连接 => 帮我们进行封装.返回值就是一个对象public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql = " from Customer c inner join fetch c.linkMens ";
Query query = session.createQuery(hql);
List<Customer> list = query.list();
System.out.println(list);//---------------------------------------------------- tx.commit();
session.close();
}
@Test//HQL 左外连接 => 将连接的两端对象分别返回.放到数组中.public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql = " from Customer c left join c.linkMens ";
Query query = session.createQuery(hql);
List<Object[]> list = query.list(); for(Object[] arr : list){
System.out.println(Arrays.toString(arr));
}//---------------------------------------------------- tx.commit();
session.close();
}
@Test//HQL 右外连接 => 将连接的两端对象分别返回.放到数组中.public void fun4(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------String hql = " from Customer c right join c.linkMens ";
Query query = session.createQuery(hql);
List<Object[]> list = query.list(); for(Object[] arr : list){
System.out.println(Arrays.toString(arr));
}//---------------------------------------------------- tx.commit();
session.close();
}
}Lernen Sie die HQL-Syntax (nicht häufig verwendet) – Multitabellen-Abfragesyntax
3. Abfrage – Kriteriengrammatik
public class Demo {
@Test//基本语法public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Criteria c = session.createCriteria(Customer.class);
List<Customer> list = c.list();
System.out.println(list); //---------------------------------------------------- tx.commit();
session.close();
}
@Test//条件语法public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Criteria c = session.createCriteria(Customer.class);
// c.add(Restrictions.idEq(2l));c.add(Restrictions.eq("cust_id",2l));
List<Customer> list = c.list();
System.out.println(list); //---------------------------------------------------- tx.commit();
session.close();
}
@Test//分页语法 - 与HQL一样public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Criteria c = session.createCriteria(Customer.class);//limit ?,? c.setFirstResult(0);
c.setMaxResults(2);
List<Customer> list = c.list();
System.out.println(list); //---------------------------------------------------- tx.commit();
session.close();
}
@Test//排序语法 public void fun4(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Criteria c = session.createCriteria(Customer.class);
c.addOrder(Order.asc("cust_id"));//c.addOrder(Order.desc("cust_id"));
List<Customer> list = c.list();
System.out.println(list); //---------------------------------------------------- tx.commit();
session.close();
}
@Test//统计语法 public void fun5(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Criteria c = session.createCriteria(Customer.class); //设置查询目标 c.setProjection(Projections.rowCount());
List list = c.list();
System.out.println(list); //---------------------------------------------------- tx.commit();
session.close();
}
}Kriteriengrammatik lernen
Nicht offline
Offline
public class Demo2 {
@Testpublic void fun1(){//Service/web层DetachedCriteria dc = DetachedCriteria.forClass(Customer.class);
dc.add(Restrictions.idEq(6l));//拼装条件(全部与普通Criteria一致) //----------------------------------------------------Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------Criteria c = dc.getExecutableCriteria(session);
List list = c.list();
System.out.println(list);//---------------------------------------------------- tx.commit();
session.close();
}
}Lernen Offline-Kriterien
4. Abfrageoptimierung
Abfrage auf Klassenebene
Get-Methode: Es gibt keine Strategie. Die Datenbank wird sofort geladen.
Lademethode: Ladestrategie auf Klassenebene anwenden
public class Demo {
@Test// get方法 : 立即加载.执行方法时立即发送sql语句查询结果public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
System.out.println(c);//---------------------------------------------------- tx.commit();
session.close();
}
@Test// load方法(默认):是在执行时,不发送任何sql语句.返回一个对象.使用该对象时,才执行查询.// 延迟加载: 仅仅获得没有使用.不会查询.在使用时才进行查询.// 是否对类进行延迟加载: 可以通过在class元素上配置lazy属性来控制.//lazy:true 加载时,不查询.使用时才查询b//lazy:false 加载时立即查询.public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Customer c = session.load(Customer.class, 2l); //---------------------------------------------------- tx.commit();
session.close();
System.out.println(c);
}
}Lazy Loading| Lazy Loading
public class Demo { //集合级别的关联//fetch:select 单表查询//lazy:true 使用时才加载集合数据. @Testpublic void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
Set<LinkMan> linkMens = c.getLinkMens();//关联级别
System.out.println(linkMens); //---------------------------------------------------- tx.commit();
session.close();
} //集合级别的关联//fetch:select 单表查询//lazy:false 立即记载集合数据 @Testpublic void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
Set<LinkMan> linkMens = c.getLinkMens();//关联级别
System.out.println(linkMens); //---------------------------------------------------- tx.commit();
session.close();
}//集合级别的关联//fetch:select 单表查询//lazy:extra 极其懒惰.与懒加载效果基本一致. 如果只获得集合的size.只查询集合的size(count语句) @Testpublic void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
Set<LinkMan> linkMens = c.getLinkMens();//关联级别
System.out.println(linkMens.size());
System.out.println(linkMens); //---------------------------------------------------- tx.commit();
session.close();
}//集合级别的关联//fetch:join 多表查询//lazy:true|false|extra 失效.立即加载. @Testpublic void fun4(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
Customer c = session.get(Customer.class, 2l);
Set<LinkMan> linkMens = c.getLinkMens();//关联级别
System.out.println(linkMens.size());
System.out.println(linkMens); //---------------------------------------------------- tx.commit();
session.close();
}
@Test//fetch: subselect 子查询//lazy: true 懒加载public void fun5(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
String hql = "from Customer";
Query query = session.createQuery(hql);
List<Customer> list = query.list(); for(Customer c:list){
System.out.println(c);
System.out.println(c.getLinkMens().size());
System.out.println(c.getLinkMens());
} //---------------------------------------------------- tx.commit();
session.close();
}
@Test//fetch: subselect 子查询//lazy: false 立即加载public void fun6(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
String hql = "from Customer";
Query query = session.createQuery(hql);
List<Customer> list = query.list(); for(Customer c:list){
System.out.println(c);
System.out.println(c.getLinkMens().size());
System.out.println(c.getLinkMens());
} //---------------------------------------------------- tx.commit();
session.close();
}
@Test//fetch: subselect 子查询//lazy: extra 极其懒惰public void fun7(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
String hql = "from Customer";
Query query = session.createQuery(hql);
List<Customer> list = query.list(); for(Customer c:list){
System.out.println(c);
System.out.println(c.getLinkMens().size());
System.out.println(c.getLinkMens());
} //---------------------------------------------------- tx.commit();
session.close();
}
}Lazy Loading- und Crawling-Strategie auf Assoziationsebene (Kunde erhält wieder mehrere Kontakte)
public class Demo2 {
@Test//fetch:select 单表查询//lazy:proxy //customer-true 懒加载public void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
LinkMan lm = session.get(LinkMan.class, 3l);
Customer customer = lm.getCustomer();
System.out.println(customer); //---------------------------------------------------- tx.commit();
session.close();
}
@Test//fetch:join 多表//lazy: 失效 public void fun3(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
LinkMan lm = session.get(LinkMan.class, 3l);
Customer customer = lm.getCustomer();
System.out.println(customer); //---------------------------------------------------- tx.commit();
session.close();
}
@Test//fetch:select 单表查询//lazy:proxy //customer-false 立即加载public void fun2(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
LinkMan lm = session.get(LinkMan.class, 3l);
Customer customer = lm.getCustomer();
System.out.println(customer); //---------------------------------------------------- tx.commit();
session.close();
}
}Lazy Loading & Fetching-Strategie auf Assoziationsebene (Kundengewinnung durch Kontakte)
Fazit: Um die Effizienz zu verbessern, sollte „Lazy“ ausgewählt werden Bei der Auswahl von „fetch“ sollte der Wert „true“ sein.
Problemlösung ohne Sitzung:
Anzahl der Crawls
public class Demo {
@Testpublic void fun1(){
Session session = HibernateUtils.openSession();
Transaction tx = session.beginTransaction();//----------------------------------------------------
String hql = "from Customer ";
Query query = session.createQuery(hql);
List<Customer> list = query.list(); for(Customer c:list){
System.out.println(c.getLinkMens());
} //---------------------------------------------------- tx.commit();
session.close();
}
}5. Übung: Abfragebedingungen zur Kundenliste hinzufügen
Fügen Sie basierend auf dem Code der letzten Notiz Filterbedingungen hinzu, bevor Sie die Kundenliste anzeigen:
Servlet-Layer-Code
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//1获得查询条件String cust_name = request.getParameter("cust_name");//2判断查询条件是否不为空DetachedCriteria dc = DetachedCriteria.forClass(Customer.class); if(cust_name!=null && !"".equals(cust_name)){
dc.add(Restrictions.like("cust_name", "%"+cust_name+"%"));
}//不为空=>添加条件//3 调用Service查询所有客户List<Customer> list = cs.getAll(dc);//4 将客户列表放入request域request.setAttribute("list", list);//5 转发到list.jsp显示request.getRequestDispatcher("/jsp/customer/list.jsp").forward(request, response);
}Service-Layer-Code
public List<Customer> getAll(DetachedCriteria dc) {
Session session = HibernateUtils.getCurrentSession();//打开事务Transaction tx = session.beginTransaction();
List<Customer> list = customerDao.getAll(dc); //关闭事务 tx.commit();return list;
}Dao Ebenencode
Das obige ist der detaillierte Inhalt vonJava-Abfragetypen, HQL, Kriterien, Abfrageoptimierung und Übungen zum Hinzufügen von Abfragebedingungen zu Kundenlisten. Für weitere Informationen folgen Sie bitte anderen verwandten Artikeln auf der PHP chinesischen Website!
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