【Hibernate】Hibernate查询语言HQL详解

╰半橙微兮° 2022-08-01 06:08 224阅读 0赞

# 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);
    }