Hibernate總結

2019-11-11 04:45:17

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hibernate設計及ORM（摘錄）

** ORM：Object–Relation–Mapping對象關系映射

對象指的就是java的實體對象; 關系指的是關系型數據庫。（Oracle、DB2、MySQL、SqlServer） ORM的主要思想就是將程序中的對象和數據庫中的數據實現自動映射轉換。利用ORM工具，在查詢時，可以自動將記錄封裝成Java對象返回。在更新、插入操作時，可以將對象自動寫入數據表。對于中間的 SQL+JDBC操作細節，完全封裝在工具底層

hibernate幾個架構 1）POJO類

public class hibernate_test { public String name; public int age; public String sex; public hibernate_test() { } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } @Override public String toString() { return "hibernate_test [name=" + name + ", age=" + age + ", sex=" + sex + "]"; }}

2）hibernate_cfg.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 package="hibernate_001"> <class name="hibernate_test" table="HIBERNATE_TEST"> <id name="name" type="java.lang.String"> <column name="NAME" /> </id> <PRoperty name="age" type="int"> <column name="AGE" /> </property> <property name="sex" type="java.lang.String"> <column name="SEX" /> </property> </class> </hibernate-mapping>

3）*.hbm.xml

<hibernate-configuration><session-factory>  <property name="connection.driver_class"></property> <property name="connection.url"></property>  <property name="connection.username">用戶名</property> <property name="connection.passWord">密碼</property>  <property name="dialect">org.hibernate.dialect.Oracle10gDialect</property>  <property name="show_sql">true</property>  <property name="hbm2ddl.auto">create</property>  <mapping resource="xxx"/></session-factory></hibernate-configuration>

使用hibernate的優勢 :不再需要大量的sql語句，實體類跟數據庫之間實現自動映射轉換

hibernate調用API **1.創建 Configuration對象 2.創建session工廠 3.通過工廠創建會話對象 4.獲取事物對象 5.進行操作，提交，結束及關閉Session**

Configuration cfg=new Configuration();SessionFactory sf=cfg.configure().buildSessionFactory();Session session=sf.openSession();session.beginTransaction();

常用的ID generator 1.identity 遞增 2.sequence 只限oracle 3.native 跨數據庫時使用 4.assigned 用戶自定義id

其他如foreign，sequence，Hilo

hibernate7大關聯映射不多作介紹，詳見：

http://blog.csdn.net/t1012665655/article/details/54574441

hibernate緩存機制

“session緩存”即hibernate的一級緩存，sessionfactory即二級緩存，同時二級緩存適合存放：常量數據，幾乎不再修改的數據，非并發訪問的數據

詳見:

http://www.cnblogs.com/wean/archive/2012/05/16/2502724.html

Hibernate查詢(摘錄)

*a.HQL查詢

Hibernate Query LanguageHQL與SQL語句結構相似，SQL語句是面向數據表和字段進行查詢，而HQL語句是面向Hibernate映射過來的對象進行查詢，因此HQL被稱為是一種面向對象查詢語言HQL和SQL共同點： --都支持select,from,where,order by,having,group by等子句。 --都支持運算符表達式，例如+,-,*,/,>,<等 --都支持in,not in,between and,like等過濾條件關鍵字 --都支持分組函max,min,sum,avg,countHQL和SQL不同點： --HQL是大小寫敏感的，類名和屬性名嚴格區分大小寫 --HQL不支持select * 寫法 --HQL不支持join...on...中的on子句，因為join...on發生在多表操作，而 Hibernate中對于有關系的多張表已將將關聯映射寫在了xxx.hbm.xml 中，在查詢時會自動加上join..on --HQL不支持表名和字段名public class TestHQL { Configuration cfg=new Configuration(); SessionFactory sFactory=cfg.configure().buildSessionFactory(); //@Test public void save(){ Session session=sFactory.openSession(); session.beginTransaction(); //設置10個板塊 for (int i = 0; i < 10; i++) { Categroy categroy=new Categroy(); categroy.setName("c"+i); session.save(categroy); } //設10個主題 for (int i = 0; i <10; i++) { Categroy c=new Categroy(); c.setId(1); Topic topic=new Topic(); topic.setCategroy(c); topic.setName("t"+i); session.save(topic); } //設10個對應回復 /*for (int i = 0; i < 10; i++) { Topic t=new Topic(); t.setId(1); Msg msg=new Msg(); msg.setMess("m"+i); msg.setTopic(t); session.save(msg); }*/ session.getTransaction().commit(); session.close(); } //@Test public void Test01(){ Session session=sFactory.openSession(); session.beginTransaction(); Query query=session.createQuery("from Categroy"); List<Categroy> categroys=query.list(); for(Categroy c:categroys){ System.out.println(c.getName()); } session.getTransaction().commit(); session.close(); } /** *查詢多個屬性，動態構建一個對象,必須要有有參，無參構造器 * */ // @Test public void Test02(){ Session session=sFactory.openSession(); session.beginTransaction(); String sql="select new Topic(id,name,categroy) from Topic"; Query query=session.createQuery(sql); List<Topic> topics=query.list(); for(Topic c:topics){ System.out.println(c); } session.getTransaction().commit(); session.close(); } /** * 對象查詢，條件查詢 * 參數的順序從0開始 */ // @Test public void test03(){ Session session = sFactory.openSession(); String hql = "select * from Dept where name=?"; Query query = session.createQuery(hql); query.setString(0,"hfz"); List<Topic> topics = query.list(); for (Topic d :topics) { System.out.println(d); } session.getTransaction().commit(); session.close(); } /** * 對象查詢，條件查詢 */ //@Test public void test04(){ Session session = sFactory.openSession(); String hql = "select * from Dept where name=? and id=?"; Query query = session.createQuery(hql); query.setString(0,"hfz").setInteger(1,1).list(); List<Topic> topics = query.list(); for (Topic d :topics) { System.out.println(d); } session.getTransaction().commit(); session.close(); } /** * 查詢所有板塊信息 * 分頁查詢 * setFirstResult();確定查詢的起點 * setMaxResult();確定查詢的條數 */ @Test public void test05(){ Session session = sFactory.openSession(); int currentPage = 5; int pageSize = 5; List<Categroy> categroys = session.createQuery("from Categroy"). setFirstResult((currentPage-1)*pageSize). setMaxResults(pageSize).list(); for (Categroy c : categroys) { System.out.println(c.getName()); } session.getTransaction().commit(); session.close(); } }

當然，現在與之類似的mybatis也用的越來越多，倆者的對比也是沒玩沒了，到最后無非還是那句話，能抓老鼠的貓就是一只好貓 引用mybatis作者的話即：

If you are starting a new project and you’re in full control of your object model and database design, Hibernate is a good choice of O/R tool. If you are accessing any 3rd party databases (e.g. vendor supplied), or you’re working with a legacy database, or even just a really poorly designed database, then an O/R mapper might not be capable of handling the situation. That’s were an SQL Mapper comes in handy

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