没有基础表的Hibernate实体 [英] Hibernate entities without underlying tables

问题描述

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。

I have a really ugly legacy database system that I need to integrate with. Essentially I'm doing some read only reporting on the system, and I don't want to set up a thousand entities representing each of the tables that I'm working on. Instead, I'd like to just define an Entity for each of the report-types that I generate (essentially a union of a bunch of columns from different tables), and then let hibernate map from the nasty (many joined, many unioned) sql query to a list of such entities.

问题是：我可以创建一个没有基础表的实体，并使用sql语句填充一个所述实体的清单？

The question is: can I create an entity that doesn't have an underlying table, and use a sql statement to populate a list of said entities?

谢谢！

推荐答案

我们这样做一直都是这样 - 以下是我们如何做的事情：

We do that sort of thing all the time - and here is how we do it:

1. 定义一个类似bean的简单对象来表示每个报告中的输出行：

1. Define a simple bean-like object to represent each row of output in your report:

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; }
}

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

Define a hibernate mapping file, 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>

然后运行查询并填充实例：

Then run the query and populate instances:

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;
}

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