在hibernate中設置：
查詢數據庫每次最多返回50條結果：
<property name=”hibernate.jdbc.fetch_size”>50</property>
30條更新數據庫一次:
<property name= ”hibernatejdbc.batch_size”>30</property>
但不是所有的數據庫都支持的，sqlServer 和orcale 都支持的。
一．hibernate 抓取策略(Fetch) 單端代理批量抓取
1.fetch=”select” 關聯(lián)實體
//fetch 默認是select
<many-to-one name="businessId" column="business_id" insert="true" update="true" fetch="select">
Student student = (Student)session.load(Student.class,1);
System.out.println(student.getName());
System.out.println(student.getClasses().getName()); //多對一中的屬性班級，獲取班級名稱
Fetch=”select” ,上面程序會發(fā)2條sql語句，第二條發(fā)送一條select語句抓取當前對象關聯(lián)實體或集合 (這里指是班級名稱)
2.fetch=” join” 關聯(lián)實體
//fetch 設置成 join
<many-to-one name="businessId" column="business_id" insert="true" update="true"
fetch=" join ">
Student student = (Student)session.load(Student.class,1);
System.out.println(student.getName());
System.out.println(student.getClasses().getName()); //多對一中的屬性班級，獲取班級名稱
fetch=” join” , 上面程序會發(fā)1條sql語句， hibernate會通過select使用外鏈接來加載其關聯(lián)實體或集合，此時lazy會失效
二．hibernate 抓取策略(Fetch) 集合代理批量抓取
1. fetch=”select”
//fetch 默認是select
<set name="students" inverse="true" cascade="all" fetch="select">
<key column="classid" />
<one-to-many class="com.Student" />
</set>
Classes cla = (Classes)session.load(Classes.class,1);
System.out.println(cla.getName());
for(Iterator iter = cla.getStudents().iterator();iter.hasNext();){
Student student = (Student)iter.next();
System.out.println(student.getName());
}
fetch=”select” ,上面程序用到了就發(fā)sql語句,第二從循環(huán)中發(fā)了N條,如果：fetch=”subselect”,則只是發(fā)送一條語句，見下面
2 fetch=”join”
//fetch 設置成join
<set name="students" inverse="true" cascade="all" fetch="join">
<key column="classid" />
<one-to-many class="com.Student" />
</set>
Classes cla = (Classes)session.load(Classes.class,1);
System.out.println(cla.getName());
for(Iterator iter = cla.getStudents().iterator();iter.hasNext();){
Student student = (Student)iter.next();
System.out.println(student.getName());
}
Fetch=”select” ,上面程序只發(fā)了一條sql語句
三．hibernate 抓取策略(Fetch) 集合代理批量抓取
2. fetch=”subselect”
//fetch設置成subselect
<set name="students" inverse="true" cascade="all" fetch="subselect">
<key column="classid" />
<one-to-many class="com.Student" />
</set>
List classesList = session.createQuery(“select c from Classes c where c.id in(1,2,3)”);
for(Iterator iter=classesList.iterator();iter.hasNext();){
Classess classess = (Classess)iter.next();
System.out.println(“classes.name=”+ classes.getName());
for(Iterator iter1 = classess.getStudents().iterator();iter1.hasNext();){
Student student = (Student)iter1.next();
System.out.println(student.getName());
}
}
Fetch=”subselct” ,另外發(fā)送一條select語句抓取在前面查詢到的所有實體對象的關聯(lián)集合
四．hibernate 批量策略batch-size屬性，可以批量加載實體類，
參見Classes.hbm.xml，同時集合也可以是使用，如：
<set name="students" inverse="true" cascade="save-update" batch-size=”5”>
在配置文件hbm.xml 設置中：
<class name="com.Classes " table="tb_classes" batch-size=”3”>
List students = session.createQuery(“select s from Student s where s.id in(:ids)”).setParameterList(“:ids”,new Object[]{1,11,21,31,41,51,61,71,81,91}).list();
for(Iterator iter=students.iterator();iter.hasNext();){
Student student = (Sutdent)iter.next();
System.out.println(student.getName());
System.out.println(student.getClassess().getName());
}
當第二個for循環(huán)時，每次加載 之前設置的 數量 實體對象, 如：現(xiàn)在設置3，那么當Iterator iter=students.iterator();iter.hasNext();時候，他會查詢出3個student對象