问为什么JPA实体类会有一个带有实体名称和下划线的类
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Stack Overflow用户

提问于 2014-04-27 17:16:23

回答 3查看 11.7K关注 0票数 9

我是JPA的新手，我已经创建了一个类，如下所示

/**
 * 
 */
package programme;

import javax.persistence.Access;
import javax.persistence.AccessType;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.persistence.Transient;

/**
 * @author anoop
 *
 */
@Entity
@Table(name="course")
@Access(AccessType.FIELD)
public class programme {
    @Id private int id;
    private String name;
    private int year;
    @Transient private String comments;

    //getters and setters for the fields.
}

我注意到还有另一个类，它的名称是我的实体java类Programme.java，带有下划线，即Programme_.java。这个类是什么?为什么会生成这个类。有什么办法可以阻止它的产生吗？

Programme_.java类的代码如下所示。

package programme;

import javax.annotation.Generated;
import javax.persistence.metamodel.SingularAttribute;
import javax.persistence.metamodel.StaticMetamodel;

@Generated(value="Dali", date="2014-04-27T21:32:59.433+0530")
@StaticMetamodel(programme.class)
public class programme_ {
    public static volatile SingularAttribute<programme, Integer> id;
    public static volatile SingularAttribute<programme, String> name;
    public static volatile SingularAttribute<programme, Integer> year;
    public static volatile SingularAttribute<programme, String> comments;
}

database-schema

java

hibernate

jpa

回答 3

Stack Overflow用户

回答已采纳

发布于 2014-04-28 01:38:33

这就是你的“规范元模型”。它可以与JPA Criteria API一起使用，如JPA2.x规范(第6.2节)所述。

要阻止Eclipse生成这些类:编辑Eclipse项目属性> JPA > Canonical metamodel (JPA 2.0) > Source folder -将文件夹的值设置为"“。

票数 14

Stack Overflow用户

发布于 2015-08-31 21:07:28

这是我对persistence.xml所做的更改，以避免生成带有下划线的Java文件和类文件(这导致了我的a problem)：

diff --git a/examples/javaee7/src/main/resources/META-INF/persistence.xml b/examples/javaee7/src/main/resources/META-INF/persistence.xml
index 86d3c0c..a477432 100644
--- a/examples/javaee7/src/main/resources/META-INF/persistence.xml
+++ b/examples/javaee7/src/main/resources/META-INF/persistence.xml
@@ -1,9 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <persistence version="2.1" xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
     <persistence-unit name="javaee7addressbookPersistenceUnit" transaction-type="JTA">
-        <exclude-unlisted-classes>false</exclude-unlisted-classes>
+        <exclude-unlisted-classes>true</exclude-unlisted-classes>
         <properties>
             <property name="javax.persistence.schema-generation.database.action" value="create"/>
         </properties>
     </persistence-unit>
 </persistence>

在此更改之前，将生成以下文件：

target/generated-sources/annotations/com/greptilian/addressbookmvc/javaee7/Person_.java
target/classes/com/greptilian/addressbookmvc/javaee7/Person_.class

票数 0

Stack Overflow用户

发布于 2021-12-08 05:42:13

除了ones生成之外(如Brian Vosburgh所提到的)，JPA元模型可以在maven构建期间生成，例如由JPA Static Metamodel Generator生成。如果maven依赖项

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-jpamodelgen</artifactId>
    <version>CURRENT-VERSION</version>
</dependency>