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Question

我目前正在学习如何使用Hibernate将对象存储在数据库中。我在https://netbeans.org/kb/docs/java/hibernate-java-se.html上读了一篇教程，并试图为一个非常简单的类和表创建一个XML文件。然而，我完全无法让它开始工作，我现在真的很沮丧。我就是没法让它起作用。

数据库是Postgres 9.2，类是我自己编写的，Hibernate的版本是Netbeans 7.3附带的版本(我相信是3.2)。

下表如下：

CREATE TABLE sellable.manufacturers
(
  mfr_id serial NOT NULL, -- Manufacturer ID
  mfr_name character varying(127) NOT NULL, -- Manufacturer name
  CONSTRAINT manufacturers_pkey PRIMARY KEY (mfr_id),
  CONSTRAINT manufacturers_mfr_name_key UNIQUE (mfr_name)
);

我试图将它映射到的类如下：

package bikeshop.sellable;

import java.io.Serializable;

public class Manufacturer implements Serializable {
    private Integer mfrId   = null;
    private String  mfrName = null;

    public Integer getMfrId () {
        return this.mfrId;
    }

    public String getMfrName () {
        return this.mfrName;
    }

    public void setMfrName (String MfrName) {
        this.mfrName    = MfrName;
    }
}

Hibernate映射的XML是：

<?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 Aug 21, 2013 7:20:20 PM by Hibernate Tools 3.2.1.GA -->
<hibernate-mapping>
    <class name="bikeshop.sellable.Manufacturer" table="manufacturers" schema="sellable">
        <comment>Product manufacturers</comment>
        <id name="mfrId" type="int">
            <column name="mfr_id" />
            <generator class="assigned" />
        </id>
        <property name="mfrName" type="string">
            <column name="mfr_name" length="127" not-null="true" unique="true">
                <comment>Manufacturer name</comment>
            </column>
        </property>
    </class>
</hibernate-mapping>

Hibernate项目配置是：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>
    <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</property>
    <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>
    <property name="hibernate.connection.url">jdbc:postgresql://localhost/bikeshop</property>
    <property name="hibernate.connection.username">bikeshop</property>
    <property name="hibernate.connection.password">bikeshop</property>
    <property name="hibernate.show_sql">true</property>
    <property name="hibernate.query.factory_class">org.hibernate.hql.classic.ClassicQueryTranslatorFactory</property>
    <property name="hibernate.format_sql">true</property>
    <mapping class="bikeshop.sellable.Manufacturer" file="" jar="" package="" resource="bikeshop/mappings/Manufacturers.hbm.xml"/>
    <mapping resource="bikeshop/mappings/Sellables.hbm.xml"/>
  </session-factory>
</hibernate-configuration>

当我尝试使用HQL查询编辑器时，我得到的只是显示的查询"select from“，这显然无法执行。试图执行它会导致异常。

org.hibernate.exception.SQLGrammarException:无法执行查询

为什么这不能生成有效的SQL查询？我遗漏了什么？

编辑:我一直在努力让这个工作，现在我得到了一个不同的错误。HQL查询窗口现在显示消息“无法从数据库检索数据”。异常已更改为"org.hibernate.PropertyNotFoundException:未能在类bikeshop.sellable.Manufacturer中找到属性mfrId的setter“。

配置文件已更改为：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
  <session-factory>
    <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</property>
    <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>
    <property name="hibernate.connection.url">jdbc:postgresql://localhost/bikeshop</property>
    <property name="hibernate.connection.username">bikeshop</property>
    <property name="hibernate.connection.password">bikeshop</property>
    <property name="hibernate.show_sql">true</property>
    <property name="hibernate.query.factory_class">org.hibernate.hql.classic.ClassicQueryTranslatorFactory</property>
    <property name="hibernate.format_sql">true</property>
    <mapping class="bikeshop.sellable.Manufacturer" file="" jar="" package="bikeshop.sellable" resource="bikeshop/mappings/manufacturer.hbm.xml"/>
  </session-factory>
</hibernate-configuration>

映射文件已更改为：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
  <class name="bikeshop.sellable.Manufacturer" table="manufacturers" schema="sellable">
        <comment>Product manufacturers</comment>
        <id name="mfrId" type="int">
            <column name="mfr_id" />
            <generator class="native" />
        </id>
        <property name="mfrName" type="string">
            <column name="mfr_name" length="127" not-null="true" unique="true">
                <comment>Manufacturer name</comment>
            </column>
        </property>
  </class>
</hibernate-mapping>

编辑2:作为最后的尝试，我将所有制造商成员公开，并将访问类型更改为XML中的字段。

现在，HQL查询工作并返回结果。但我显然不想采取这种方法，公共领域是一个可怕的想法！

Answer 1

问题似乎在于，在对类或其元数据进行更改时，HQL编辑器并不总是得到更新的类或元数据，不管您是使用外部XML文件还是内联注释，都可能发生这种情况。

到目前为止，我找到的唯一解决办法是退出Netbeans并重新启动它。这使得HQL查询编辑器更新，但显然很烦人。