常用的HQL語句

HQL: Hibernate Query Language.

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性。
3，HQL的關鍵字不區分大小寫，類名與屬性名是區分大小寫的。
4，SELECT可以省略.

1，簡單的查詢

Employee為實體名而不是數據庫中的表名(面向對象特性)

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"; 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"; // 相當于"FROM Employee e" hql = "SELECT e.name 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 hql = "SELECT e.id,e.name FROM Employee e"; // 查詢多個列，返回的集合的元素類型是Object數組 hql = "SELECT new Employee(e.id,e.name) FROM Employee e"; // 可以使用new語法，指定把查詢出的部分屬性封裝到對象中

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); // 等同于 limit 0,10 兩種查詢結果list、uniqueResultList list = query.list(); // 查詢的結果是一個List集合 Employee employee = (Employee) query.uniqueResult();// 查詢的結果是唯一的一個結果，當結果有多個，就會拋異常

6，方法鏈

List list = session.createQuery("FROM Employee e").setFirstResult(0).setMaxResults(10).list();

7，聚集函數

count(), max(), min(), avg(), sum()

hql = "SELECT COUNT(*) FROM Employee"; // 返回的結果是Long型的 hql = "SELECT min(id) FROM Employee"; // 返回的結果是id屬性的類型

8，分組: Group By … Having

hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name"; hql = "SELECT e.name,COUNT(e.id) FROM Employee e GROUP BY e.name HAVING count(e.id)>1"; hql = "SELECT e.name,COUNT(e.id) FROM Employee e WHERE id<9 GROUP BY e.name HAVING count(e.id)>1"; 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 " + "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

9，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 JOIN e.department d";hql = "SELECT e.id,e.name,d.name FROM Employee e INNER 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";

右外連接（outer關鍵字可以省略）

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";

10，查詢時使用參數

方式一：使用’?’占位

hql = "FROM Employee e WHERE id BETWEEN ? AND ?";List list2 = session.createQuery(hql).setParameter(0, 5)// 設置參數，第1個參數的索引為0。.setParameter(1, 15).list();

方式二：使用變量名

hql = "FROM Employee e WHERE id BETWEEN :idMin AND :idMax";List list3 = session.createQuery(hql).setParameter("idMax", 15).setParameter("idMin", 5).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 list4 = session.createQuery(hql).setParameterList("ids", new Object[] { 1, 2, 3, 5, 8, 100 }).list();

11，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。

Delete

int result1 = 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。

工具類：將HQL語句轉換為SQL語句

/** * 將hql 語句轉換為sql語句 * @param hql 要轉換的 hql語句 */ public String transHqlToSql(String hql){SessionFactoryImpl sfi = (SessionFactoryImpl)awMixThrProDao.getSessionD().getSessionFactory();QueryTranslatorFactory qtf = sfi.getSettings().getQueryTranslatorFactory();FilterTranslator qt = qtf.createFilterTranslator(hql, hql, null, sfi);qt.compile( null, false );System. out.println(" hql==>sql: " +qt.getSQLString());return qt.getSQLString(); }

HQL生成工具類

/*** 根據實體構建hql 語句* @author lxl* @createTime 2013-05 -10 16:00* @version 1.0*/ public class BuildHqlUtil {/*** 根據實體生成對應的hql語句，對象中具有值的屬性將成為查詢的限制條件部分<br/>* 其中，對于String類型的屬性是 like 判斷的，以其開頭的：like '[value]%'* @param entity* @return*/@SuppressWarnings( "unchecked")public static String buildSelectStr(Object entity) {return buildSelectStr(entity, null);}/*** 根據實體生成有字段限制的 hql語句，對象中具有值的屬性將成為查詢的限制條件部分<br/>* 其中，對于String類型的屬性是 like 判斷的，以其開頭的：like '[value]%'* @param entity* @param queryFields 數組形式的查詢字段：select xxx,xxx ...* @return*/@SuppressWarnings( "unchecked")public static String buildSelectStr(Object entity, String[] queryFields) {if (entity == null) {try {throw new Exception("實體不能為null");} catch (Exception e) {e.printStackTrace();return null ;}}Class clazz = entity.getClass();String hqlStr = "";try {Field[] fields = clazz.getDeclaredFields();Field.setAccessible(fields, true);hqlStr = getFieldMsg(fields, queryFields) + getWhereMsg(entity, fields, queryFields);} catch (Exception e) {e.printStackTrace();}return hqlStr;}/*** 構建查詢字段* @param fields* @param queryFields* @return* @throws Exception*/private static String getFieldMsg(Field[] fields, String[] queryFields)throws Exception {String selectStr = "";int i, j;if (queryFields != null && queryFields.length != 0) {selectStr = "select ";for (i = 0; i < queryFields.length ; i++) {if (!"" .equals(queryFields[i])) {boolean flag = false;for (j = 0; j < fields.length; j++) {if (queryFields[i].equals(fields[j].getName())) {flag = true;}}if (flag) {selectStr += queryFields[i] + ",";} else {throw new Exception("實體中不存在該字段：" + queryFields[i]);}}}if ("select " .equals(selectStr)) {selectStr = "";} else {selectStr = selectStr.substring(0, selectStr.length() - 1)+ " ";}}return selectStr;}/*** 構建查詢條件** @param entity* @param fields* @param queryFields* @return* @throws IllegalArgumentException* @throws IllegalAccessException*/private static String getWhereMsg(Object entity, Field[] fields, String[] queryFields)throws IllegalArgumentException, IllegalAccessException {String whereStr = "from " + entity.getClass().getSimpleName() + " where 1=1";for (int i = 0; i < fields.length; i++) {if (fields[i].get(entity) == null || fields[i].get(entity).toString().trim().length() == 0) {continue;}String value = fields[i].get(entity).toString();String field = fields[i].getName();if (isNum(fields[i].getType().getName())) {whereStr += " and " + field + "=" + value;} else {whereStr += " and " + field + " like '" + value + "%'";}}return whereStr;}/*** 判斷是否為Integer，Double，Float等數字類型，注意都是封裝類型* @param fieldName* @return*/private static boolean isNum(String fieldName) {boolean flag = false;if (fieldName.endsWith(".Integer" )|| fieldName.endsWith( ".Double")|| fieldName.endsWith( ".Float")|| fieldName.endsWith( ".Long")|| fieldName.endsWith( ".Number")|| fieldName.endsWith( ".BigDecimal")) {flag = true;}return flag;}}

一點注意

關于Hibernate執行帶有join的HQL語句：

Query query = session.createQuery("select c from Custom as c join c.orders as ord where ord.name = : name"); query.setString("name", "1213233"); List list = query.list(); for(int i=0;i<list.size();i++){Custom custom = (Custom)list.get(i); }

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