Hibernate的檢索策略
立即檢索、延遲檢索，預先抓取和批量檢索都是為了優化加載性能而設置的策略。立即加載、延遲加載、預先抓取是同一級別的策略，因為它們是三選一的策略。用了其中一個則另外兩個就不可用了，而且被延遲加載的對象當最終被加載時，一定是使用了立即加載的形式。如果在配置文件中設置了對某個屬性的預先抓取，則對此屬性的其他加載設置全部失效（比如還設置了延遲加載，此時失效）。批量檢索可以優化立即檢索和延遲加載，它們可以同時使用，即批量立即加載和批量延遲加載
立即檢索 類級別的立即加載關聯對象 關聯級別的立即加載指定對象的關聯對象可以設定批量檢索數量
延時檢索 類級別的延時加載關聯對象 關聯級別的延時加載指定對象的關聯對象可以設定批量檢索數量
迫切左外連接檢索 類級別不適用關聯級別通過左外連接加載與檢索方法指定對象關聯的對象
涉及到的元素屬性
<class>和<set>的lazy 默認是true 表示延時檢索
<many-to-one><one-to-one><set> 的 outer-join <many-to-one><one-to-one>默認auto <set> 默認 false
<class>和<set>的batch-size默認1 指定批量檢索的數量
' 延時檢索時會產生代理類
' 但是僅僅初始化了OID 其他都為null
' 只有當訪問除ID外的屬性或者修改時才會加載數據庫的數據
' 有可能在你關閉session后仍沒有初始化對象也就沒有完整的游離對象
' 只有在session范圍內才能被初始化
' get()方法加載的對象時實際相關數據不是代理類
一對多和多對多的檢索策略
<set> 的lazy和out-join
都為false 立即檢索
lazy為false out-join為true是迫切左外連接檢索(當有多個<set>只允許一個用)
相反時用延時檢索策略
Hibernate的檢索方式
HQL檢索方式：
1 通過Session的createQuery()方法創建一個Query對象包含一HQL查詢語句
2 可以動態綁定參數
3 可以調用list()方法返回List類型的結果
exp :
List result = session.createQuery(".......").setString("name",name).setInteger("age", 21).list();
QBC檢索方式：
1 用session的才createCriteria()方法創建一個Criteria對象
2 可以設定查詢的條件用Expression的一些靜態方法如Expression.like("name", "T%")
Expression.eq("age", new Integer(21)
3 可以使用方法鏈也可以調用list()方法返回List類型的結果
exp :
List result = session.createCriteria(Customer.class).add(Restrictions.like("name", "T%")).add(Restrictions.eq("age", new Integer(21)).list();
4 還可以使用QBE模板檢索方式
exp :
Customer exp = new Customer();
exp.setName("tom");
List result =session.createCriteria(Customer.class).add(Example.create(exp)).list();
SQL檢索方式：
Query query=session.createSQLQuery("..............");
由于檢索和HQL比較雜亂分別舉例說明
' 最簡單的查詢
HQL
Session session=sessionFactory.openSession();
Transaction tx=null;
try
{
tx=session.beginTransaction();
List result=session.createQuery("from Customer ").list();
for(Iterator it=result.iterator(); it.hasNext();)
{
Customer c =(Customer)it.next();
System.out.println("Customer's name :" + c.getName());
System.out.println("Customer's age :" + c.getAge());
}
tx.commit();
}
catch(Exception e)
{
if(tx!=null)
{
tx.rollback();
}
throw e;
}
BQC
...
List result=session.createCriteria(Customer.class).list();
...
' 指定查詢和命名別名
HQL
...
List result=session.createQuery("from Customer as c where name=:name").setString("name", "Tom").list();
...
BQC
...
List result=session.createCriteria(Customer.class).add(Restrictions.eq("name", "Tom")).list();
...
' 對查詢結果排序
desc是降序
HQL
...
List result=session.createQuery("from Customer as c order by c.name").list();
List result=session.createQuery("from Customer as c order by c.name asc, c.age desc").list();
...
BQC
...
List result=session.createCriteria(Customer.class).addOrder(Order.asc("name")).addOrder(Order.desc("age")).list();
...
' 在指定時間范圍內查詢結果
...
tx=session.beginTransaction();
Date beginDate=java.sql.Date.valueOf("2006-8-1");
Date endDate=java.sql.Date.valueOf("2006-9-1");
List result=session.createQuery("from Customer c where c.retime <:endTime and c.retime >=:beginTime").setTimestamp("endTime", endDate).setTimestamp("beginTime", beginDate).list();
...
' 分頁查詢
HQL
...
List result=session.createQuery("from Customer c Order by c.name asc").setFirstResult(0).setMaxResults(3).list();
...
BQC
...
List result=session.createCriteria(Customer.class).addOrder(Order.asc("name")).setFirstResult(0).setMaxResults(3).list();
...
' 檢索單個對象
uniqueResult() 方法
如果不確定返回的時單個對象先用Query和Criteria的serMaxResult(1)方法設定只返回一個對象
如果確定只返回一個對象比如from Customer c where c.id＝1
' HQL的兩種綁定查詢
1
session.createQuery("from Customer c where c.name=:name and c.age=:age").setString("name", "tom").setInteger("age", 20)
2
session.createQuery("from Customer c where c.name=? and c.age=?").setString(0, "tom").setInteger(1, 20)
' 特殊綁定方法
1
setEntity() 可以綁定實體對象
session.createQuery("from Order o where o.customer=:customer").setEntity("customer", customer)
2
setParameter 綁定任意類型的參數
Query query=session.createQuery("from Order o where o.customer=:customer and o.orderNumber like: orderNumber ");
query.setParameter("customer", customer, Hibernate.entity(Customer.class));
query.setParameter("orderNumber", orderNumber, Hibernate.STRING)；
3
setProperties() 與一個對象的屬性綁定
Customer customer = new Customer();
customer.setName("Tom");
customer.setAge(21);
List result=session.createQuery("from Customer c where c.name=:name and c.age=:age").setProperties(customer).list();
' 設定查詢條件
' 比較運算大于某個條件
HQL
...
List result=session.createQuery("from Customer c where c.age>23").list();
...
BQC
...
List result=session.createCriteria(Customer.class).add(Restrictions.gt("age", new Integer(23))).list();
...
' 比較運算不等于某個條件
HQL
...
List result=session.createQuery("from Customer c where c.age<>24").list();
...
BQC
...
List result=session.createCriteria(Customer.class).add(Restrictions.not(Restrictions.eq("age", new Integer(23)))).list();
...
' 比較運算條件為null的某個對象
HQL
...
List result=session.createQuery("from Order o where o.customer is null").list();
...
BQC
...
List result=session.createCriteria(Order.class)
.add(Restrictions.isNull("customer")).list();
...
' 范圍運算檢索在某個范圍內String
HQL
...
List result=session.createQuery("from Customer c where c.name in('Tom','Mike','Jack')").list();
...
BQC
...
String[] names={"Tom", "Mike", "Jack"};
List result=session.createCriteria(Customer.class)
.add(Restrictions.in("name", names)).list();
...
' 范圍運算檢索在某個范圍內Integer
HQL
...
List result=session.createQuery("from Customer c where c.age between 24 and 30").list();
...
BQC
...
List result=session.createCriteria(Customer.class)
.add(Restrictions.between("age", new Integer(24), new Integer(30))).list();
...
不在某個范圍內
HQL
...
List result=session.createQuery("from Customer c where c.age not between 24 and 30").list();
...
BQC
...
List result=session.createCriteria(Customer.class)
.add(Restrictions.not(Restrictions.between("age", new Integer(24), new Integer(30)))).list();
...
' 范圍運算字符串通配符
以 T 開頭
HQL like 'T%'
BQC add(Restrictions.like("name","T%"))
以 T 結尾
HQL like '%T'
BQC add(Restrictions.like("name","%T"))
包含 T
HQL like '%T%'
BQC add(Restrictions.like("name","%T%"))
控制長度為3
HQL like 'T_ _'
BQC add(Restrictions.like("name","T_ _"))
另外
Restrictions 還有這樣的方法like(java.lang.String propertyName, java.lang.String value, MatchMode matchMode)
有一些定義好的field 具體查看API
' 邏輯運算檢索復雜條件
條件結合
HQL
...
List result=session.createQuery("from Customer c where c.name like 'T%' and c.name like '%m'").list();
...
BQC
...
List result=session.createCriteria(Customer.class)
.add(Restrictions.like("name", "T%")).add(Restrictions.like("name", "%m")).list();
...
邏輯與
Restriction有如下方法
or(Criterion lhs, Criterion rhs)
and(Criterion lhs, Criterion rhs
HQL
...
List result=session.createQuery("from Customer c where (c.name like 'T%' and c.name like '%m') or (c.age not between 20 and 25)").list();
...
BQC
...
List result=session.createCriteria(Customer.class).add(Restrictions.or(Restrictions.and(Restrictions.like("name", "T%"), Restrictions.like("name", "%m")), Restrictions.not(Restrictions.between("age", new Integer(20), new Integer(25))))).list();
...
' 報表查詢
from 關鍵字是必須 select group by having 用于報表查詢
投影查詢只檢索出需要的字段
HQL
...
List result=session.createQuery("select c.id, c.name, o.orderNumber from Customer c join c.orders o where o.orderNumber like 'T%'").list();
Iterator it=result.iterator();
while(it.hasNext())
{
Object[] row=(Object[])it.next();
Long id=(Long)row[0];
String name=(String)row[1];
String orderNumber=(String)row[2];
System.out.println(id+" "+name+" "+orderNumber);
}
...
這個list返回的結果是集合存放的是關系數據
也可以建立一個javabean來讓結果更清晰
...
select new ergal.CustomerRow(c.id, c.name, o.orderNumber) from Customer c join c.orders o where o.orderNumber like 'T%'
...
while(it.hasNest())
{
CustomerRow cr=(CustomerRow)it.next();
Long id=(Long)cr.getId();
......
}
' 分組查詢
查詢相同姓名的的記錄
...
List result=session.createQuery("select c.name, count(c) from Customer c group by c.name").list();
Iterator it=result.iterator();
while(it.hasNext())
{
Object[] row=(Object[])it.next();
String name=(String)row[0];
Long id=(Long)row[1];
System.out.println(id+" "+name);
}
...
統計訂單數目
...
List result=session.createQuery("select c.id, c.name, count(o) from Customer c join c.orders o group by c.id").list();
Iterator it=result.iterator();
while(it.hasNext())
{
Object[] row=(Object[])it.next();
Long id=(Long)row[0];
String name=(String)row[1];
Long num=(Long)row[2];
System.out.println(num+" "+name+" "+id);
}
...
統計每個客戶的訂單總價-右外連接
...
List result=session.createQuery("select c.id, c.name, sum(o.price) from Customer c right outer join c.orders o group by c.id").list();
Iterator it=result.iterator();
while(it.hasNext())
{
Object[] row=(Object[])it.next();
Long id=(Long)row[0];
String name=(String)row[1];
Double num=(Double)row[2];
System.out.println(num+" "+name+" "+id);
}
...
統計每個客戶的訂單總價-加條件訂單大于一的
...
List result=session.createQuery("select c.id, c.name, sum(o.price) from Customer c join c.orders o group by c.id having(count(o)>1)").list();
Iterator it=result.iterator();
while(it.hasNext())
{
Object[] row=(Object[])it.next();
Long id=(Long)row[0];
String name=(String)row[1];
Double num=(Double)row[2];
System.out.println(num+" "+name+" "+id);
}
...
查詢時間段
tx=session.beginTransaction();
Date beginDate=java.sql.Date.valueOf("2006-8-1");
Date endDate=java.sql.Date.valueOf("2006-9-1");
List result=session.createQuery("from Customer c where c.retime <:endTime and c.retime >=:beginTime").setTimestamp("endTime", endDate).setTimestamp("beginTime", beginDate).list();
for(Iterator it=result.iterator(); it.hasNext();)
{
Customer c =(Customer)it.next();
System.out.println("Customer's name :" + c.getName());
System.out.println("Customer's regiestertime :" + c.getRetime());
}
總的來說就是將顯示時間和數據庫的時間都進行轉化然后進行比較
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posted on 2007-09-16 14:52
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