步骤3：适配思路

集成datanucleus和jdo相关的jar包，在demo上增加一个查询接口，测试是否可行。

官方文档如下：https://www.datanucleus.org/products/accessplatform/jdo/tutorial.html#step4

我的适配项目：https://gitcode.com/chenzhida/opensource-demo-datanucleus-241206/overview?ref=dev_jdo

分支：dev_jdo

步骤3：适配过程的问题

问题1：启动应用，报错：无法找到Meta-data

Caused by: org.datanucleus.exceptions.NucleusUserException: Found Meta-Data for class org.apache.servicecomb.fence.resource.Student but this class is either not enhanced or you have multiple copies of the persistence API jar in your CLASSPATH!! Make sure all persistable classes are enhanced before running DataNucleus and/or the CLASSPATH is correct.

解决：这是因为datanucleus需要预先在编译阶段，执行增强，命令：mvn datanucleus:enhance，注意只需要到用到的模块执行这行命令即可。

问题2：在执行mvn datanucleus:enhance，报错：

plugin:5.2.1:enhance (default-cli) on project resource-server: The DataNucleus tool org.datanucleus.enhancer.DataNucleusEnhancer exited with a non-null exit code. -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.datanucleus:datanucleus-maven-plugin:5.2.1:enhance (default-cli) on project resource-server: The DataNucleus tool org.datanucleus.enhancer.DataNucleusEnhancer exited with a non-null exit code.
    at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute2 (MojoExecutor.java:333)
    at org.apache.maven.lifecycle.internal.MojoExecutor.doExecute (MojoExecutor.java:316)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:212)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:174)
    at org.apache.maven.lifecycle.internal.MojoExecutor.access$000 (MojoExecutor.java:75)
    at org.apache.maven.lifecycle.internal.MojoExecutor$1.run (MojoExecutor.java:162)
    at org.apache.maven.plugin.DefaultMojosExecutionStrategy.execute (DefaultMojosExecutionStrategy.java:39)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:159)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:105)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:73)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:53)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:118)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:261)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:173)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:101)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:906)

这里出现过很多次，这是因为各个jar包的版本不兼容，参考官网案例上使用的版本

步骤4：添加接口

添加一个接口，能够在不同实例上返回不同的值。

// 配置bean
@Bean
public PersistenceManagerFactory persistenceManagerFactory() {
        return JDOHelper.getPersistenceManagerFactory("myJDOUnit");
    }

public Student findStudentById(Long id) {
        PersistenceManager pm = pmf.getPersistenceManager();
        Transaction tx = pm.currentTransaction();
        Student result = null;

        try {
            tx.begin();

            // 创建 JDOQL 查询
            Query query = pm.newQuery(Student.class, "id == :id");
            query.setUnique(true); // 确保查询结果唯一

            // 执行查询
            result = (Student) query.execute(id);

            tx.commit();
        } catch (Exception e) {
            if (tx.isActive()) {
                tx.rollback();
            }
            e.printStackTrace();
        } finally {
            pm.close();
        }

        return result;
    }

// 配置xml
<?xml version="1.0" encoding="UTF-8" ?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence" version="2.1">
  <persistence-unit name="myJDOUnit">
    <class>org.apache.servicecomb.fence.resource.Student</class>
    <properties>
      <property name="javax.jdo.option.ConnectionURL" value="jdbc:postgresql://ip:port/postgres?currentSchema=class" />
      <property name="javax.jdo.option.ConnectionDriverName" value="org.postgresql.Driver" />
      <property name="javax.jdo.option.ConnectionUserName" value="root" />
      <property name="javax.jdo.option.ConnectionPassword" value="pwd" />
      <!-- DataNucleus 配置 -->
      <property name="datanucleus.schema.autoCreateAll" value="true"/>
      <property name="datanucleus.schema.autoCreateColumns" value="true"/>
      <property name="datanucleus.validateTables" value="false"/>
      <property name="datanucleus.validateConstraints" value="false"/>
    </properties>
  </persistence-unit>
</persistence>

步骤6：购买华为云Gaussdb和ECS，上云测试

购买华为云Gaussdb，并且购买公网IP，不然无法访问。配置如下：