Question

我正在尝试建立一个基本的JPA。但我甚至无法得到EntityManger。以下配置可能出现什么问题？

private static final EntityManager emf = Persistence
.createEntityManagerFactory("transactions-optional").createEntityManager();

src/META-INF/persistence.xml（也尝试过：src/main/webapp/WEB-INF/classes/META-INF/）：

<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence
        http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd" version="1.0">

    <persistence-unit name="transactions-optional">
        <provider>org.datanucleus.api.jpa.PersistenceProviderImp</provider>
        <properties>
            <property name="datanucleus.NontransactionalRead" value="true"/>
            <property name="datanucleus.NontransactionalWrite" value="true"/>
            <property name="datanucleus.ConnectionURL" value="appengine"/>
        </properties>
    </persistence-unit>
</persistence>

结果：

Caused by: javax.persistence.PersistenceException: No Persistence provider for EntityManager named transactions-optional
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:54)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:32)
    at de.verism.server.database.EMFService.<clinit>(EMFService.java:13)

Maven配置：

   <dependency>
        <groupId>javax.jdo</groupId>
        <artifactId>jdo2-api</artifactId>
        <version>2.3-eb</version>
        <exclusions>
            <!--
                exclude the legacy javax.transaction:transaction-api
                and replace it with javax.transaction:jta (it
                appears to be the same thing)
            -->
            <exclusion>
                <groupId>javax.transaction</groupId>
                <artifactId>transaction-api</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
    <dependency>
        <groupId>javax.transaction</groupId>
        <artifactId>jta</artifactId>
        <version>1.1</version>
    </dependency>
    <dependency>
        <groupId>com.google.appengine.orm</groupId>
        <artifactId>datanucleus-appengine</artifactId>
        <version>2.1.2</version>
    </dependency>
    <dependency>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-core</artifactId>
        <version>3.2.4</version>
        <exclusions>
            <exclusion>
                <groupId>javax.transaction</groupId>
                <artifactId>transaction-api</artifactId>
            </exclusion>
        </exclusions>
    </dependency>
    <dependency>
        <groupId>com.google.appengine</groupId>
        <artifactId>datanucleus-jpa</artifactId>
        <version>1.1.5</version>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>com.google.appengine</groupId>
        <artifactId>geronimo-jpa_3.0_spec</artifactId>
        <version>1.1.1</version>
        <scope>runtime</scope>
    </dependency>
    <dependency>
        <groupId>com.google.appengine</groupId>
        <artifactId>appengine-api-1.0-sdk</artifactId>
        <version>${gae.version}</version>
    </dependency>

更新了配置：

        <dependency>
            <groupId>com.google.appengine.orm</groupId>
            <artifactId>datanucleus-appengine</artifactId>
            <version>2.1.1</version>
        </dependency>
        <dependency>
            <groupId>org.datanucleus</groupId>
            <artifactId>datanucleus-core</artifactId>
            <version>3.1.1</version>
        </dependency>
        <dependency>
            <groupId>org.datanucleus</groupId>
            <artifactId>datanucleus-api-jpa</artifactId>
            <version>3.1.1</version>
        </dependency>
<dependency>
    <groupId>org.apache.geronimo.specs</groupId>
    <artifactId>geronimo-jpa_2.0_spec</artifactId>
    <version>1.1</version>
    <scope>runtime</scope>
</dependency>

Answer 1

Google的datanucleus-appengine 2.1.x需要DataNucleus 3.1.x（而不是3.2.x）。你应该有jdo-api v3.x（不是jdo2-api v2.3.x）。如果使用JPA，则需要“datanucleus-api-jpa”v3.1.x（不是“datanucleus-jpa”v1.x）。您还需要“geronimo-jpa-2.0_spec”v1.x（不是geronimo-jpa-3.0_spec v1.x）。

是的，我认为你完全可以messed up the dependencies ;-) 然后，当您修复了使用GAE docs设置持久性提供程序

时

Answer 2

我认为问题是提供者类

中缺少 l

＆LT;提供商GT; org.datanucleus.api.jpa.PersistenceProviderImp的升＆LT; /提供商GT;

Answer 3

我有同样的问题。查看META-INF，有两个名为：

的文件

jdoconfig.xml
的persistence.xml

如果您正在使用持久性api，那么您可以通过在jdoconfig.xml文件中添加块注释来消除此错误

没有EntityManager的持久性提供程序？

3 个答案: