Hibernate查询语言HQL详解

常用的HQL语句

HQL: Hibernate Query Language.

特点：
1，与SQL相似，SQL中的语法基本上都可以直接使用。
2，SQL查询的是表和表中的列；HQL查询的是对象与对象中的属性。
3，HQL的关键字不区分大小写，类名与属性名是区分大小写的。
4，SELECT可以省略.

1，简单的查询

Employee为实体名而不是数据库中的表名(面向对象特性)

hql = "FROM Employee";hql = "FROM Employee AS e"; // 使用别名hql = "FROM Employee e"; // 使用别名，as关键字可省略

2，带上过滤条件的（可以使用别名）：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，带上排序条件的：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"; // 相当于"FROM Employee e"hql = "SELECT e.name FROM Employee e"; // 只查询一个列，返回的集合的元素类型就是这个属性的类型hql = "SELECT e.id,e.name FROM Employee e"; // 查询多个列，返回的集合的元素类型是Object数组hql = "SELECT new Employee(e.id,e.name) FROM Employee e"; // 可以使用new语法，指定把查询出的部分属性封装到对象中

5，执行查询

获得结果（list、uniqueResult、分页 ）

Query query = session.createQuery("FROM Employee e WHERE id<3");query.setFirstResult(0);query.setMaxResults(10); // 等同于 limit 0,10两种查询结果list、uniqueResult List list = query.list(); // 查询的结果是一个List集合Employee employee = (Employee) query.uniqueResult();// 查询的结果是唯一的一个结果，当结果有多个，就会抛异常

6，方法链

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

7，聚集函数

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

hql = "SELECT COUNT(*) FROM Employee"; // 返回的结果是Long型的hql = "SELECT min(id) FROM Employee"; // 返回的结果是id属性的类型

8，分组: 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子句中不能使用列别名     "ORDER BY c ASC"; // 在orderby子句中可以使用列别名

9，连接查询

HQL是面向对象的查询

内连接（inner关键字可以省略）

 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";

左外连接（outer关键字可以省略）

 hql = "SELECT e.id,e.name,d.name FROM Employee e LEFT OUTER JOIN e.department d";

右外连接（outer关键字可以省略）

 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，查询时使用参数

方式一：使用’?’占位

 hql = "FROM Employee e WHERE id BETWEEN ? AND ?"; List list2 = session.createQuery(hql)     .setParameter(0, 5)// 设置参数，第1个参数的索引为0。     .setParameter(1, 15)     .list();

方式二：使用变量名

 hql = "FROM Employee e WHERE id BETWEEN :idMin AND :idMax"; List list3 = session.createQuery(hql)     .setParameter("idMax", 15)     .setParameter("idMin", 5)     .list();// 当参数是集合时，一定要使用setParameterList()设置参数值 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与delete，不会通知Session缓存

Update

int result = session.createQuery(        "UPDATE Employee e SET e.name=? WHERE id>15")        .setParameter(0, "无名氏")        .executeUpdate(); // 返回int型的结果，表示影响了多少行。

Delete

int result1 = session.createQuery(//        "DELETE FROM Employee e WHERE id>15")        .executeUpdate(); // 返回int型的结果，表示影响了多少行。

工具类：将HQL语句转换为SQL语句

/*** 将hql 语句转换为sql语句* @param hql 要转换的 hql语句*/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生成工具类

/** * 根据实体构建hql 语句 * @author lxl * @createTime 2013-05 -10 16:00 * @version 1.0 */public class BuildHqlUtil {    /**     * 根据实体生成对应的hql语句，对象中具有值的属性将成为查询的限制条件部分<br/>     * 其中，对于String类型的属性是 like 判断的，以其开头的：like '[value]%'     * @param entity     * @return     */    @SuppressWarnings( "unchecked")    public static String buildSelectStr(Object entity) {        return buildSelectStr(entity, null);    }    /**     * 根据实体生成有字段限制的 hql语句，对象中具有值的属性将成为查询的限制条件部分<br/>     * 其中，对于String类型的属性是 like 判断的，以其开头的：like '[value]%'     * @param entity     * @param queryFields 数组形式的查询字段：select xxx,xxx ...     * @return     */    @SuppressWarnings( "unchecked")    public static String buildSelectStr(Object entity, String[] queryFields) {        if (entity == null) {            try {                throw new Exception("实体不能为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;    }    /**     * 构建查询字段     * @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("实体中不存在该字段：" + queryFields[i]);                    }                }            }            if ("select " .equals(selectStr)) {                selectStr = "";            } else {                selectStr = selectStr.substring(0, selectStr.length() - 1)                        + " ";            }        }        return selectStr;    }    /**     * 构建查询条件     *     * @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;    }    /**     * 判断是否为Integer，Double，Float等数字类型，注意都是封装类型     * @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;    }}

一点注意

关于Hibernate执行带有join的HQL语句：

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);}