Hibernate的抓取策略

1.1、 區(qū)分延遲和立即檢索:

立即檢索:

* 當(dāng)執(zhí)行某行代碼的時(shí)候,馬上發(fā)出SQL語(yǔ)句進(jìn)行查詢(xún).

* get()

延遲檢索:

* 當(dāng)執(zhí)行某行代碼的時(shí)候,不會(huì)馬上發(fā)出SQL語(yǔ)句進(jìn)行查詢(xún).當(dāng)真正使用這個(gè)對(duì)象的時(shí)候才會(huì)發(fā)送SQL語(yǔ)句.

* load();

1.2、類(lèi)級(jí)別檢索和關(guān)聯(lián)級(jí)別檢索:

類(lèi)級(jí)別的檢索:

* ＜class>標(biāo)簽上配置lazy

關(guān)聯(lián)級(jí)別的檢索:

* <set>/<many-to-one>上面的lazy.

1.2.1、從一的一方關(guān)聯(lián)多的一方:

* <set>

* fetch:控制sql語(yǔ)句的類(lèi)型

* join:發(fā)送迫切左外連接的SQL查詢(xún)關(guān)聯(lián)對(duì)象.fetch=”join”那么lazy被忽略了.

* select:默認(rèn)值,發(fā)送多條SQL查詢(xún)關(guān)聯(lián)對(duì)象.

* subselect:發(fā)送子查詢(xún)查詢(xún)關(guān)聯(lián)對(duì)象.(需要使用Query接口測(cè)試)

* lazy:控制關(guān)聯(lián)對(duì)象的檢索是否采用延遲.

* true:默認(rèn)值, 查詢(xún)關(guān)聯(lián)對(duì)象的時(shí)候使用延遲檢索

* false:查詢(xún)關(guān)聯(lián)對(duì)象的時(shí)候不使用延遲檢索.

* extra:及其懶惰.

如果fetch是join的情況,lazy屬性將會(huì)忽略.

1.2.2、在多的一方關(guān)聯(lián)一的一方:

* <many-to-one>

* fetch:控制SQL語(yǔ)句發(fā)送格式

* join:發(fā)送一個(gè)迫切左外連接查詢(xún)關(guān)聯(lián)對(duì)象.fetch=”join”,lay屬性會(huì)被忽略.

* select:發(fā)送多條SQL檢索關(guān)聯(lián)對(duì)象.

* lazy:關(guān)聯(lián)對(duì)象檢索的時(shí)候,是否采用延遲

* false:不延遲

* proxy:使用代理.檢索訂單額時(shí)候,是否馬上檢索客戶(hù) 由Customer對(duì)象的映射文件中<class>上lazy屬性來(lái)決定.

* no-proxy:不使用代理

測(cè)試：

package com.sihai.hibernate3.test;import java.util.List;import org.hibernate.Hibernate; import org.hibernate.Session; import org.hibernate.Transaction; import org.junit.Test;import com.sihai.hibernate3.demo1.Customer; import com.sihai.hibernate3.demo1.Order; import com.sihai.utils.HibernateUtils;/*** Hibernate的抓取策略* * @author sihai* */ public class HibernateTest4 {@SuppressWarnings("unchecked")@Test// 批量抓取:// 從訂單批量抓取客戶(hù)// 在Customer.hbm.xml中<class>標(biāo)簽上設(shè)置batch-size=""public void demo9(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// 查詢(xún)所有的訂單:List<Order> list = session.createQuery("from Order").list();for (Order order : list) {System.out.println(order.getCustomer().getCname());}tx.commit();session.close();}@Test// 批量抓取:// 從客戶(hù)批量抓取訂單// <set>標(biāo)簽上設(shè)置batch-size=""public void demo8(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// 查詢(xún)所有客戶(hù)List<Customer> list = session.createQuery("from Customer").list();for (Customer customer : list) {for (Order order : customer.getOrders()) {System.out.println(order.getAddr());}}tx.commit();session.close();}@Test// 在Order.hbml.xml中<many-to-one>標(biāo)簽上配置fetch和lazypublic void demo7(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();/*** fetch="select",lazy="false"*/// 查詢(xún)一號(hào)訂單//Order order = (Order) session.get(Order.class, 1);// 發(fā)送多條SQL查詢(xún)關(guān)聯(lián)對(duì)象// 查詢(xún)一號(hào)訂單所屬客戶(hù)的名稱(chēng)://System.out.println("客戶(hù)名稱(chēng):"+order.getCustomer().getCname());// 不發(fā)送SQL/*** fetch="select",lazy="proxy"* proxy:查詢(xún)關(guān)聯(lián)對(duì)象的時(shí)候,是否采用延遲,由另一端的類(lèi)級(jí)別延遲來(lái)決定.* * Customer的<class>上配置的是lazy="true".檢索的時(shí)候采用延遲* * Customer的<class>上配置的是lazy="false".檢索的時(shí)候不采用延遲*/// 查詢(xún)一號(hào)訂單Order order = (Order) session.get(Order.class, 1);// 發(fā)送多條SQL查詢(xún)關(guān)聯(lián)對(duì)象// 查詢(xún)一號(hào)訂單所屬客戶(hù)的名稱(chēng):System.out.println("客戶(hù)名稱(chēng):"+order.getCustomer().getCname());// 不發(fā)送SQLtx.commit();session.close();}@Test// 在Order.hbml.xml中<many-to-one>標(biāo)簽上配置fetch和lazypublic void demo6(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();/*** fetch="join",lazy被忽略.*/// 查詢(xún)一號(hào)訂單Order order = (Order) session.get(Order.class, 1);// 發(fā)送一條迫切左外連接查詢(xún)關(guān)聯(lián)對(duì)象.// 查詢(xún)一號(hào)訂單所屬客戶(hù)的名稱(chēng):System.out.println("客戶(hù)名稱(chēng):"+order.getCustomer().getCname());tx.commit();session.close();}@SuppressWarnings("unchecked")@Test// 在Customer.hbm.xml的<set>標(biāo)簽上配置fetch和lazy// fetch="subselect" 子查詢(xún)public void demo5(){Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();/*** 配置fetch="subselect" lazy="true"*/ // List<Customer> list = session.createQuery("from Customer").list();// 發(fā)送查詢(xún)所有客戶(hù)的SQL // for (Customer customer : list) { // System.out.println("客戶(hù)訂單數(shù)量:"+customer.getOrders().size());// 發(fā)送一個(gè)子查詢(xún)?nèi)ゲ樵?xún)關(guān)聯(lián)對(duì)象. // }// 使用子查詢(xún) 查詢(xún)多個(gè)的情況./*Customer customer = (Customer) session.get(Customer.class, 1);System.out.println("客戶(hù)訂單數(shù)量:"+customer.getOrders().size());*//*** 配置fetch="subselect" lazy="false"*/ // List<Customer> list = session.createQuery("from Customer").list();// 發(fā)送查詢(xún)所有客戶(hù)的SQL,發(fā)送一個(gè)子查詢(xún)查詢(xún)訂單 // for (Customer customer : list) { // System.out.println("客戶(hù)訂單數(shù)量:"+customer.getOrders().size());// 不發(fā)送SQL // }/*** 配置fetch="subselect" lazy="extra"*/List<Customer> list = session.createQuery("from Customer").list();// 發(fā)送查詢(xún)所有客戶(hù)的SQLfor (Customer customer : list) {System.out.println("客戶(hù)訂單數(shù)量:"+customer.getOrders().size());// 只發(fā)送統(tǒng)計(jì)客戶(hù)訂單數(shù)量的sqlfor (Order order : customer.getOrders()) {System.out.println(order.getAddr());}}tx.commit();session.close();}@Test// 在Customer.hbm.xml的<set>標(biāo)簽上配置fetch和lazy// fetch="select"public void demo4() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();/*** 配置fetch="select" lazy="true"* * 發(fā)送多條SQL.默認(rèn)值就是fetch="select" lazy="true"*/// 查詢(xún)一號(hào)客戶(hù)// Customer customer = (Customer) session.get(Customer.class, 1);//發(fā)送一條查詢(xún)客戶(hù)的SQL// 查看一號(hào)客戶(hù)的訂單的數(shù)量:// System.out.println("訂單的數(shù)量:" + customer.getOrders().size());//又發(fā)送一條查詢(xún)訂單的SQL/*** 配置fetch="select" lazy="false"*/// 查詢(xún)一號(hào)客戶(hù)//Customer customer = (Customer) session.get(Customer.class, 1);//發(fā)送多條SQL查詢(xún)// 查看一號(hào)客戶(hù)的訂單的數(shù)量://System.out.println("訂單的數(shù)量:" + customer.getOrders().size());//不發(fā)送SQL/*** 配置fetch="select" lazy="extra"* * extra:及其懶惰的.*/// 查詢(xún)一號(hào)客戶(hù)Customer customer = (Customer) session.get(Customer.class, 1);// 發(fā)送一條查詢(xún)客戶(hù)的SQL// 查看一號(hào)客戶(hù)的訂單的數(shù)量:System.out.println("訂單的數(shù)量:" + customer.getOrders().size());// 查詢(xún)訂單的數(shù)量:select count(oid) from orders o where o.cid = ? for (Order order : customer.getOrders()) {System.out.println(order);}tx.commit();session.close();}@Test// 在Customer.hbm.xml的<set>標(biāo)簽上配置fetch和lazy// fetch="join",lazy的取值就會(huì)被忽略.public void demo3() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// 查詢(xún)一號(hào)客戶(hù)Customer customer = (Customer) session.get(Customer.class, 1);// 發(fā)送了一條迫切左外連接的SQL// 查看一號(hào)客戶(hù)的訂單的數(shù)量:System.out.println("訂單的數(shù)量:" + customer.getOrders().size());// 不發(fā)送SQL.tx.commit();session.close();}@Test// 默認(rèn)的情況下 沒(méi)有配置任何信息// 發(fā)送多條SQL查詢(xún)其關(guān)聯(lián)對(duì)象.public void demo2() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// 查詢(xún)一號(hào)客戶(hù)Customer customer = (Customer) session.get(Customer.class, 1);// 發(fā)送一條查詢(xún)客戶(hù)的SQL.// 查看一號(hào)客戶(hù)的訂單的數(shù)量:System.out.println("訂單的數(shù)量:" + customer.getOrders().size());// 使用訂單的時(shí)候,又會(huì)發(fā)送一條SQL查詢(xún)tx.commit();session.close();}@Test// 區(qū)分立即和延遲檢索public void demo1() {Session session = HibernateUtils.openSession();Transaction tx = session.beginTransaction();// 立即檢索// Customer customer = (Customer) session.get(Customer.class, 1);// System.out.println(customer.getCname());// 延遲檢索:Customer customer = (Customer) session.load(Customer.class, 1);Hibernate.initialize(customer);System.out.println(customer.getCname());tx.commit();session.close();} }

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