本文主要說的是Session的saveOrUpdate、clear、flush等方法的使用以及控制建表語句的輸出等。
1.Session的saveOrUpdate方法
先看下hibernate的API文檔的相關描述：
void |
saveOrUpdate(Object object)
Either save() or update() the given instance, depending upon the value of its identifier property. |
看下方法發的詳解
saveOrUpdate
public void saveOrUpdate(Object object) throws HibernateException
- Either save() or update() the given instance, depending upon the value of its identifier property. By default the instance is always saved. This behaviour may be adjusted by specifying an unsaved-value attribute of the identifier property mapping. This operation cascades to associated instances if the association is mapped with cascade="save-update".
-
- Parameters:
object- a transient or detached instance containing new or updated state- Throws:
HibernateException- See Also:
save(java.lang.Object),Session#update(Object object, Serializable id)
仍然使用之前的Techer
package com.baosight.model;
import javax.persistence.Column;
import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.SequenceGenerator;
import javax.persistence.TableGenerator;
/**
* <p>Title: </p>
* <p>Description:Teacher </p>
* <p>Company: </p>
* @author yuan
* @date 2016-4-10 下午12:32:46*/
@Entity
@TableGenerator(name="tableGEN",table="table_gen",pkColumnName="pk_key",valueColumnName="pk_value",pkColumnValue="teacher",allocationSize=1)
@SequenceGenerator(name="teacherSEQ",sequenceName="teacherSEQ_DB")
//@IdClass(value=TeacherPK.class)
public class Teacher {
private String id;
private String name;
private String title;
// private TeacherPK pk;
@Id
@GeneratedValue//auto
// @GeneratedValue(strategy=GenerationType.TABLE,generator="tableGEN")
// @GeneratedValue(strategy=GenerationType.SEQUENCE,generator="teacherSEQ")
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
// @Id
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
// @Column(updatable=false)
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
// @EmbeddedId
// @Id
/*public TeacherPK getPk() {
return pk;
}
public void setPk(TeacherPK pk) {
this.pk = pk;
}*/
}
package com.baosight.model;
import static org.junit.Assert.*;
import javax.persistence.Column;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.cfg.Configuration;
import org.hibernate.tool.hbm2ddl.SchemaExport;
import org.junit.AfterClass;
import org.junit.BeforeClass;
import org.junit.Test;
/**
* <p>Title:TecherTest </p>
* <p>Description:TODO </p>
* <p>Company: </p>
* @author yuan
* @date 2016-4-13 下午10:32:17*/
public class TeacherTest {
private static SessionFactory sf = null;
@BeforeClass
public static void beforeClass(){
// 讀取配置文件
Configuration cfg = new AnnotationConfiguration();
// 得到session工廠
sf = cfg.configure().buildSessionFactory();
}
@Test
public void testSaveOrUpdate() {
// 教師測試類
Teacher t = new Teacher();
t.setName("t1");
t.setTitle("中級");
Session session = sf.getCurrentSession();
// 開啓事務
session.beginTransaction();
// session執行
session.saveOrUpdate(t);
// 事務提交
session.getTransaction().commit();
t.setName("zhangsan");
Session session1 = sf.getCurrentSession();
// 開啓事務
session1.beginTransaction();
// session執行
session1.saveOrUpdate(t);
// 事務提交
session1.getTransaction().commit();
}
@Test
public void testClear() {
//直接從數據庫查詢，會打印sql
Session session = sf.getCurrentSession();
// 開啓事務
session.beginTransaction();
// session執行
Teacher t = (Teacher) session.get(Teacher.class, "1");
System.out.println(t.getId());
session.clear();
Teacher t1 = (Teacher) session.get(Teacher.class, "1");
System.out.println(t1.getId());
System.out.println(t1==t);
// 事務提交
session.getTransaction().commit();
}
@Test
public void testFlush() {
//直接從數據庫查詢，會打印sql
Session session = sf.getCurrentSession();
// 開啓事務
session.beginTransaction();
// session執行
Teacher t = (Teacher) session.load(Teacher.class, "1");
t.setName("tttt");
session.flush();
t.setName("lisi");
session.getTransaction().commit();
// session執行
// 事務提交
}
@Test
public void testSchemaExport() {
new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
}
@AfterClass
public static void afterClass(){
// 關閉session工廠
sf.close();
}
}
調用testSaveOrUpdate，第一次調用saveOrUpdate是將transient併爲persistent，使用save；第二次調用saveOrUpdate是將detached變爲persistent，使用update。運行結果如下：
2.Session的clear方法
先看下hibernate的API的介紹
void |
clear() Completely clear the session. |
clear
public void clear()
- Completely clear the session. Evict all loaded instances and cancel all pending saves, updates and deletions. Do not close open iterators or instances of ScrollableResults.
就是說調用clear方法會清除session已經存在的所有緩存的實例
使用JUnit進行測試
調用上面的testClear方法，不使用clear時發現只做了一次查詢，結果如下：
testClear使用clear之後，發現查詢了2次
3.Session的flush方法
先看下hibernate的API的介紹
void |
flush() Force the Session to flush. |
flush
public void flush()
throws HibernateException
- Force the Session to flush. Must be called at the end of a unit of work, before commiting the transaction and closing the session (Transaction.commit() calls this method). Flushing is the process of synchronising the underlying persistent store with persistable state held in memory.
-
- Throws:
HibernateException
也就是說flush默認是在Transaction.commit()時被調用，可以通過調用Session的flush方法實現在Transaction.commit()之前就調用flush，實現數據的存儲和狀態的同步。
使用JUnit進行測試
調用上面的testFlush方法，當不使用flush時，只會在Transaction.commit()時做一次修改，結果如下：
testFlush使用flush後，後做2次修改
4.關於使用SchemaExport輸出建表語句
hibernate的配置文件hibernate.cfg.xml中可以配置hbm2ddl.auto，以實現控制建表等，具體配置如下：
<!-- Drop and re-create the database schema on startup -->
<property name="hbm2ddl.auto">update</property>當然，hibernate也可以通過代碼來實現這個過程，即使用SchemaExport
首先看下hibernate的API文檔
org.hibernate.tool.hbm2ddl
Class SchemaExport
java.lang.Object org.hibernate.tool.hbm2ddl.SchemaExport
- public class SchemaExport
- extends Object
Commandline tool to export table schema to the database. This class may also be called from inside an application.
命令行工具導出表的數據庫架構。這個類可以在應用程序中調用。構造方法
SchemaExport(Configuration cfg)
Create a schema exporter for the given Configuration
需要加載配置文件，跟使用session時差不多
實現代碼見上面的testSchemaExport方法，具體如下：
@Test
public void testSchemaExport() {
new SchemaExport(new AnnotationConfiguration().configure()).create(false, true);
}主要使用的是create方法
void |
create(boolean script, boolean export)
Run the schema creation script. |
create
public void create(boolean script,
boolean export)
- Run the schema creation script.
-
- Parameters:
script- print the DDL to the consoleexport- export the script to the database
使用JUnit測試，調用上面的testSchemaExport方法，第一個參數爲true時，結果如下：
create的第一個參數爲false時
以上即爲hibernate的除了常規的CRUD之外比較常見的方法，需要在實際的使用過程中仔細體會。
