Hibernate映射必要？(Hibernate Mapping necessary?)

 我是Hibernate的新手，我下载了一个示例Java应用程序并将其修改为更有用，到目前为止，在我的应用程序中，我有两个在我的Java应用程序中定义的db类：Actor.java和City.java每个类都有.hbm.xml文件如下所示： 
 
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Jun 17, 2009 11:42:48 AM by Hibernate Tools 3.2.1.GA -->
<hibernate-mapping>
    <class name="sakila.entity.Actor" table="actor" catalog="sakila">
        <id name="actorId" type="java.lang.Short">
            <column name="actor_id" />
            <generator class="identity" />
        </id>
        <property name="firstName" type="string">
            <column name="first_name" length="45" not-null="true" />
        </property>
        <property name="lastName" type="string">
            <column name="last_name" length="45" not-null="true" />
        </property>
        <property name="lastUpdate" type="timestamp">
            <column name="last_update" length="19" not-null="true" />
        </property>
    </class>
</hibernate-mapping>
 
 
<hibernate-mapping>
    <class name="sakila.entity.City" table="city" catalog="sakila">
        <id name="cityId" type="java.lang.Short">
            <column name="city_id" />
            <generator class="identity" />
        </id>
        <property name="city" type="string">
            <column name="city" length="45" not-null="true" />
        </property>
        <property name="countryId" type="string">
            <column name="country_Id" length="45" not-null="true" />
        </property>
        <property name="lastUpdate" type="timestamp">
            <column name="last_update" length="19" not-null="true" />
        </property>
    </class>
</hibernate-mapping>
 
 该应用程序迄今为止效果很好。 但我的问题是，如果我需要更改我的应用程序，以便它可以处理像数据库中的Actor和City等数百个对象，我需要定义所有映射文件吗？ 如果我在编程时不知道用户可能查询哪些数据库对象，我是否需要定义它们，这似乎是不可能的，所以我的问题是：是否需要* .hbm.xml文件？ 在这种情况下，我需要编写一个应用程序，让用户查询他需要的任何对象，我甚至可能不知道数据库中的内容，如何编写这样的应用程序？ Hibernate可用吗？ 

I'm new to Hibernate, I downloaded a sample Java app and modified it to be more useful, so far in my app I have two db classes that are defined in my Java app : Actor.java and City.java Each of them has a .hbm.xml file look like the following :
 
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Jun 17, 2009 11:42:48 AM by Hibernate Tools 3.2.1.GA -->
<hibernate-mapping>
    <class name="sakila.entity.Actor" table="actor" catalog="sakila">
        <id name="actorId" type="java.lang.Short">
            <column name="actor_id" />
            <generator class="identity" />
        </id>
        <property name="firstName" type="string">
            <column name="first_name" length="45" not-null="true" />
        </property>
        <property name="lastName" type="string">
            <column name="last_name" length="45" not-null="true" />
        </property>
        <property name="lastUpdate" type="timestamp">
            <column name="last_update" length="19" not-null="true" />
        </property>
    </class>
</hibernate-mapping>
 
 
 
<hibernate-mapping>
    <class name="sakila.entity.City" table="city" catalog="sakila">
        <id name="cityId" type="java.lang.Short">
            <column name="city_id" />
            <generator class="identity" />
        </id>
        <property name="city" type="string">
            <column name="city" length="45" not-null="true" />
        </property>
        <property name="countryId" type="string">
            <column name="country_Id" length="45" not-null="true" />
        </property>
        <property name="lastUpdate" type="timestamp">
            <column name="last_update" length="19" not-null="true" />
        </property>
    </class>
</hibernate-mapping>
 
The app works great so far. But my question is, what if I need to change my app so that it can handle hundreds of objects like Actor and City in the db, do I need to define all the mapping files ? What if I don't know at the time of programming what db objects user might query, do I need to define all of them, that seems impossible, so my question is : is the *.hbm.xml files necessary ? In the case I need to write an app that lets user query whatever objects he needs, and I may not even know what's in the db, how to write such an app ? Doable with Hibernate ?

原文：https://stackoverflow.com/questions/14428059