（十五）条件查询

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2024-08-16 00:11:25 212人阅读

条件查询信息列表

1、在baseDao、baseDaoImpl中编写和实现findObjects(String hql, List<Object> parameters)

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2、在service、serviceImpl中调用baseDao中的条件查询方法

3、在action中用service中新写的findObjects(String hql, List<Object> parameters)进行条件查询

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4、添加listUI.jsp中的查询方法。

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优化查询-查询工具类QueryHelper

设计一个查询工具类QueryHelper，里面需要对将要查询的hql和参数进行组装，然后将此对象传递给service运用并返回结果。该工具类主要方法有：

① QueryHelper(Class clazz, String alias) 构造器，主要组装from 子句

② addCondition(String condition, Object... param) 组装where子句

③ addOrderByProperty(String property, String order) 组装order by 子句

④ getListQueryHql() 返回查询列表的hql

⑤ getCountQueryHql() 返回统计总记录数的hql

⑥ getParameters() 返回参数列表

具体类实现：

 1 package cn.itcast.core.utils; 2  3 import java.util.ArrayList; 4 import java.util.List; 5  6 public class QueryHelper { 7      8     //from 子句 9     private String fromClause = "";10     //where 子句11     private String whereClause = "";12     //order by 子句13     private String orderByClause = "";14     15     //where 子句中?对应的参数值16     private List<Object> parameters;17     18     public static String ORDER_BY_ASC = "ASC";//升序19     public static String ORDER_BY_DESC = "DESC";//降序20     21     /**22      * 利用构造方法构造from子句23      * @param clazz 实体类24      * @param alias 别名25      */26     public QueryHelper(Class clazz, String alias){27         fromClause = "FROM " + clazz.getSimpleName() + " " + alias;28     }29     /**30      * 组装where子句31      * @param condition 条件32      * @param params 条件中?对应的参数值33      * @return QueryHelper34      */35     public QueryHelper addCondition(String condition, Object...params){36         if(whereClause.length() > 0){37             whereClause += " AND " + condition;38         } else {39             whereClause = " WHERE " + condition;40         }41         if(parameters == null){42             parameters = new ArrayList<Object>();43         }44         for(Object param: params){45             parameters.add(param);46         }47         return this;48     }49     /**50      * 构建order by 子句51      * @param property 排序的属性52      * @param order 升序(asc)或是降序(desc)53      * @return QueryHelper54      */55     public QueryHelper addOrderByProperty(String property, String order){56         if(orderByClause.length() > 0){57             orderByClause += "," + property + " " + order;58         } else {59             orderByClause += " ORDER BY " + property + " " + order;60         }61         return this;62     }63 64     //返回列表查询hql语句65     public String getListQueryHql(){66         return fromClause + whereClause + orderByClause;67     }68     69     //返回查询总记录数的hql70     public String getCountHql(){71         return "SELECT Count(*) " + fromClause + whereClause;72     }73     74     public List<Object> getParameters() {75         return parameters;76     }77 }