使用HQL查詢的特點:
(1)與SQL相似,SQL中的語法基本上都可以直接使用。
(2)SQL查詢的是表和表中的列;HQL查詢的是對象與對象中的屬
(3)HQL的關鍵字不區分大小寫,類名與屬性名是區分大小寫
(4)SELECT可以省略.
Employee類、Department類、SessionFactoryTools類、Employee.hbm.xml文件、 Department.hbm.xml文件、Hibernate.cfg.xml文件都與4中的相同。
1>簡單的數據庫的查詢:
持久化層代碼:
/**
* 員工類和部門類的持久層類
*/
public class EmpAndDepDao {
/**
* save的方法
*/
@Test
public void save() {
Session session = SessionFactoryTools.getSession(); Transaction tx = null;// 聲明一個事務
try {
tx = session.beginTransaction();// 開始一個事務
// ============================================
// 新建部門對象,設置並設置部門名稱
for (int i = 0; i < 10; i++) {
Department department = new Department();
department.setName("開發部" + i);
session.save(department);
}
// 新建員工對象,並設置姓名
for (int i = 0; i < 20; i++) {
Employee employee = new Employee();
employee.setName("趙錢孫" + i);
session.save(employee);
}
// ===============================================
tx.commit();
} catch (RuntimeException e) {
if (tx != null) {
tx.rollback();
}
throw e;
} finally {
session.close();
}
}
/**
* getById
*/
@Test
public void getById() {
Session session = SessionFactoryTools.getSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
String hql = null;
// ================================================================
// -------獲取部門信息-------------------------------------
/** 1,簡單的查詢
hql = "FROM Employee";
hql = "FROM Employee AS e"; // 使用別名
hql = "FROM Employee e"; // 使用別名,as關鍵字可省略
*/
/** 2,帶上過濾條件的(可以使用別名):Where
hql = "FROM Employee WHERE id<10";
hql = "FROM Employee e WHERE e.id<10";
hql = "FROM Employee e WHERE e.id<10 AND e.id>5";
*/
/**3,帶上排序條件的:Order By
hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name";
hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name DESC";
<span style="white-space:pre"> </span> hql = "FROM Employee e WHERE e.id<10 ORDER BY e.name DESC, id ASC";
*/
/**4,指定select子句(不可以使用select *)
hql = "SELECT e FROM Employee e"; // 相當於"FROM Employee e"
// 只查詢一個列,返回的集合的元素類型就是這個屬性的類型
<span style="white-space:pre"> </span> hql = "SELECT e.name FROM Employee e";
<span style="white-space:pre"> </span>// 查詢多個列,返回的集合的元素類型是Object數組 <span style="white-space:pre"> </span>hql = "SELECT e.id,e.name FROM Employee e";
<span style="white-space:pre"> </span>// 可以使用new語法,指定把查詢出的部分屬性封裝到對象中
<span style="white-space:pre"> </span>hql = "SELECT new Employee(e.id,e.name) FROM Employee e"; */
/** 5,執行查詢,獲得結果(list、uniqueResult、分頁 )
Query query = session.createQuery("FROM Employee e WHERE id<3");
query.setFirstResult(0);
query.setMaxResults(10);
// List list = query.list(); // 查詢的結果是一個List集合
<span style="white-space:pre"> </span>// 查詢的結果是唯一的一個結果,當結果有多個,就會拋異常
Employee employee = (Employee) query.uniqueResult(); <span style="white-space:pre"> </span>System.out.println(employee);
*/
/** 6,方法鏈
List list = session.createQuery(//
"FROM Employee")//
.setFirstResult(0)//
.setMaxResults(10)//
.list();
*/
// -----賦值語句--------------------------------
<span style="white-space:pre"> </span>hql = "SELECT new Employee (e.id,e.name) FROM Employee e";
//-------執行查詢-------------------------------
List<?> list= session.createQuery(hql).list();
// ----- 顯示結果-----------------------------------
/**
* 判斷List爲什麼類型,
<span style="white-space:pre"> </span> * 若爲數組類型則採用數組輸出方式,
<span style="white-space:pre"> </span> * 否則採用對象輸出方式
*/
for (Object obj : list) {
if (obj.getClass().isArray()) {
System.out.println(Arrays.toString((Object[]) obj));
} else {
System.out.println(obj);
}
}
// =====================================================
tx.commit();
} catch (RuntimeException e) {
tx.rollback();
throw e;
} finally {
session.close();
}
}
}
2>帶有限定條件和關聯的數據庫查詢:
查詢方法:
/**
* getById
*/
@Test
public void getById() {
Session session = SessionFactoryTools.getSession();
Transaction tx = null;
try {
tx = session.beginTransaction();
String hql = null;
// ==================================================
// -------獲取部門信息-------------------------------
/** 1,聚集函數:count(), max(), min(), avg(), sum() <span style="white-space:pre"> </span> // 返回的結果是Long型的
hql = "SELECT COUNT(*) FROM Employee";
<span style="white-space:pre"> </span> // 返回的結果是id屬性的類型
<span style="white-space:pre"> </span> hql = "SELECT min(id) FROM Employee";
<span style="white-space:pre"> </span> Number result = (Number) session.createQuery(hql).uniqueResult();
System.out.println(result.getClass());
System.out.println(result);
*/
/** 2,分組: Group By ... Having
<span style="white-space:pre"> </span> hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name";
<span style="white-space:pre"> </span> hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name HAVING count(e.id)>1";
<span style="white-space:pre"> </span> hql = "SELECT e.name,COUNT(e.id) FROM Employee e WHERE id<9 GROUP BY e.name HAVING count(e.id)>1";
<span style="white-space:pre"> </span> //------鏈式查詢語言-------------------------
hql = "SELECT e.name,COUNT(e.id) " + //
"FROM Employee e " + //
"WHERE id<9 " + //
"GROUP BY e.name " + //
"HAVING count(e.id)>1 " + //
"ORDER BY count(e.id) ASC";
---
hql = "SELECT e.name,COUNT(e.id) AS c " + //
"FROM Employee e " + //
"WHERE id<9 " + //
"GROUP BY e.name " + //
<span style="white-space:pre"> </span> "HAVING count(e.id)>1 " + // 在having子句中不能使用列別名
"ORDER BY c ASC"; // 在orderby子句中可以使用列別名
*/
/** 3,連接查詢 / HQL是面向對象的查詢
//內連接(inner關鍵字可以省略)
hql = "SELECT e.id,e.name,d.name FROM Employee e INNER JOIN e.department d";
hql = "SELECT e.id,e.name,d.name FROM Employee e JOIN e.department d";
// 左外連接(outer關鍵字可以省略)
hql = "SELECT e.id,e.name,d.name FROM Employee e LEFT OUTER JOIN e.department d";
hql = "SELECT e.id,e.name,d.name FROM Employee e LEFT JOIN e.department d";
// 右外連接(outer關鍵字可以省略)
hql = "SELECT e.id,e.name,d.name FROM Employee e RIGHT OUTER JOIN e.department d";
hql = "SELECT e.id,e.name,d.name FROM Employee e RIGHT JOIN e.department d";
// 可以使用更方便的方法
hql = "SELECT e.id,e.name,e.department.name FROM Employee e";
*/
/** 4,查詢時使用參數
//方式一:使用'?'佔位
hql = "FROM Employee e WHERE id BETWEEN ? AND ?";
List list = session.createQuery(hql)//
.setParameter(0, 5)// 設置參數,0表示爲第一個參數
.setParameter(1, 15)//1表示爲第二個參數
.list();
//方式二:使用變量名
hql = "FROM Employee e WHERE id BETWEEN :idMin AND :idMax";
List list = session.createQuery(hql)//
.setParameter("idMax", 15)//idMax表示:上邊緣
.setParameter("idMin", 5)//idMin表示:下邊緣
.list();
// 當參數是集合時,一定要使用setParameterList()設置參數值
hql = "FROM Employee e WHERE id IN (:ids)";
List list = session.createQuery(hql)//ids表示:變量名
<span style="white-space:pre"> </span>.setParameterList("ids", new Object[] { 1, 2, 3, 5, 8, 100 })
<span style="white-space:pre"> </span>.list();//數組中的數值爲變量名可以取得數值
*/
/** 5,使用命名查詢
* //需要在hbm文件中配置查詢語句
//queryByIdRange:hbm文件中配置的查詢語句的名稱
Query query = session.getNamedQuery("queryByIdRange");
query.setParameter("idMin", 3);
<span style="white-space:pre"> </span> //idMin、idMax:查詢語句中的變量名
query.setParameter("idMax", 10);
List list = query.list();
*/
/**6,update與delete,不會通知Session緩存
//Update
int result = session.createQuery(//
"UPDATE Employee e SET e.name=? WHERE id>15")//
.setParameter(0, "無名氏")//
.executeUpdate(); // 返回int型的結果,表示影響了多少行。
System.out.println("result = " + result);
//Delete
int result = session.createQuery(//
"DELETE FROM Employee e WHERE id>15")//
.executeUpdate(); // 返回int型的結果,表示影響了多少行。
System.out.println("result = " + result);
*/
// ----- 執行查詢並顯示結果----------------------------
List list = session.createQuery(hql).list();
for (Object obj : list) {
if (obj.getClass().isArray()) {
System.out.println(Arrays.toString((Object[]) obj));
} else {
System.out.println(obj);
}
}
// =====================================================
tx.commit();
} catch (RuntimeException e) {
tx.rollback();
throw e;
} finally {
session.close();
}
}
注意:在update或delete後,需要refresh(obj)一下以獲取最新的狀態
// 第一次顯示名稱
Employee employee = (Employee) session.get(Employee.class, 1);
System.out.println(employee.getName());
// update與delete,不會通知Session緩存
int result = session.createQuery(//
"UPDATE Employee e SET e.name=? WHERE id=1")//
.setParameter(0, "無名氏2")//
.executeUpdate();
System.out.println(result);
// 第二次顯示名稱
session.refresh(employee);
System.out.println(employee.getName());