没有基础表的Hibernate实体

Question

我有一个非常难看的遗留数据库系统,我需要与之集成.基本上我在系统上做一些只读报告,我不想设置代表我正在处理的每个表的一千个实体.相反,我想为我生成的每个报告类型定义一个实体(实质上是来自不同表的一堆列的联合),然后让hibernate映射来讨厌(许多已加入,很多联合) sql查询到这样的实体列表.

问题是:我可以创建一个没有基础表的实体,并使用sql语句填充所述实体的列表吗？

谢谢!

Answer 1

我们一直这样做 - 这就是我们如何做到的:

1. 定义一个简单的类bean对象来表示报表中的每一行输出:

   public class CityStateRevenueReport {
   
       private String mId;
       private String mState;
       private String mCity;
       private Double mRevenue;
   
       public String getId() { return mId; }
       public void setId(String i) { mId = i; }
       public String getState() { return mState; }
       public void setState(String s) { mState = s; }
       public String getCity() { return mCity; }
       public void setCity(String c) { mCity = c; }
       public Double getReveneue() { return mRevenue; }
       public void setRevneue(Double d) { mRevenue = d; }
   }
   

2. 定义一个hibernate映射文件,CityStateRevneueReport.hbm.xml:

   <?xml version="1.0" ?>
   <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd&quot;>
   <hibernate-mapping>
       <class entity-name="CityStateRevenueReport">
           <id name="Id" type="java.lang.String" column="report_id">
               <generator class="sequence" />
           </id>
           <property name="city" type="string" column="city" />
           <property name="state" type="string" column="state" />
           <property name="revenue" type="double" column="revenue" />
       </class>
       <sql-query name="runReport">
           <![CDATA[ 
           SELECT {r.*} FROM 
               (select some_id_value as report_id, 
                       state_abbreviation as state, 
                       city_name as city, 
                       dollar_amount as revenue 
                  from -- tables, joins, other SQL insanity 
                ) r
           ]]>
           <return alias="r" class="CityStateRevenueReport" />
       </sql-query>
   </hibernate-mapping>
   

3. 然后运行查询并填充实例:

   public List<CityStateRevenueReport> runReport() {
   
       List<CityStateRevenueReport> reports = 
                                new ArrayList<CityStateRevenueReport>();
       List<HashMap> maps = session.getNamedQuery("runReport").list()
       for ( HashMap map : results ) {
           CityStateRevenueReport report = new CityStateRevenueReport();
           report.setState(map.get("state"));
           report.setCity(map.get("city"));
           report.setRevenue(Double.parseDouble(map.get("revenue"));
           reports.add(report);
       }
       return reports;
   }