为什么@Transactional不起作用，但手动编写它确实适用于此 jakarta api

问：

我目前正在雅加达尝试一些事情，似乎遇到了一个我无法弄清楚也无法在网上找到的障碍。

我正在尝试检索 de PostgreSQL DB 中的客户列表，这可以通过手动编写事务或使用 @Transactional 注释来完成。但是，手动实现正在工作，而 没有。@Transactional

我这样编写了手动事务：

package com.example.demo.service;

import com.example.demo.dto.CustomerDto;
import com.example.demo.mapper.CustomerMapper;
import jakarta.enterprise.context.ApplicationScoped;
import jakarta.persistence.EntityManager;
import jakarta.persistence.EntityManagerFactory;
import jakarta.persistence.Persistence;
import jakarta.persistence.PersistenceContext;
import jakarta.transaction.Transactional;
//import javax.transaction.Transactional;
import models.Customer;


import java.util.ArrayList;
import java.util.List;

@ApplicationScoped
public class CustomerRepository {
    EntityManagerFactory entityManagerFactory = null;
    EntityManager entityManager = null;

    public List<CustomerDto> findAllManual() {
        entityManagerFactory = Persistence.createEntityManagerFactory("jpa-postgres");
        entityManager = entityManagerFactory.createEntityManager();

        entityManager.getTransaction().begin();
        List<Customer> customers = entityManager.createQuery("SELECT c FROM Customer c", Customer.class)
                .getResultList();
        List<CustomerDto> customerDtos = new ArrayList<>();
        customers.forEach(t -> customerDtos.add(CustomerMapper.toDto(t)));
        System.out.println("Komt hier wel. Print evt entity manager: " + entityManager);
        System.out.println("Komt hier wel. Print evt costumers: " + customers);
        System.out.println("Komt hier wel. Print evt costumersDTO: " + customerDtos);
        entityManager.close();
        return customerDtos;
    }

这恰如其分地返回了我的列表。但以下情况除外。

package com.example.demo.service;

import com.example.demo.dto.CustomerDto;
import com.example.demo.mapper.CustomerMapper;
import jakarta.enterprise.context.ApplicationScoped;
import jakarta.persistence.Persistence;
import jakarta.persistence.PersistenceContext;
import jakarta.transaction.Transactional;
//import javax.transaction.Transactional;
import models.Customer;


import java.util.ArrayList;
import java.util.List;

@ApplicationScoped
public class CustomerRepository {

    @PersistenceContext(unitName = "jpa-postgres")
    private EntityManager em;

    @Transactional
    public List<CustomerDto> findAll() {
                List customers = em.createQuery("SELECT c FROM Customer c", Customer.class)
                .getResultList();
        List<CustomerDto> customerDtos = new ArrayList<>();
        customers.forEach(t -> customerDtos.add(CustomerMapper.toDto((Customer) t)));
        System.out.println("Komt hier wel. Print evt entity manager: " + em);
        System.out.println("Komt hier wel. Print evt costumers: " + customers);
        System.out.println("Komt hier wel. Print evt costumersDTO: " + customerDtos);
        return customerDtos;
    }

}

这将返回一个空列表。我认为问题出在哪里@Transactional方法不连接到数据库，这就是为什么返回一个空列表。但我似乎无法弄清楚为什么会这样。

persistence.xml ：

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<persistence xmlns="https://jakarta.ee/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="https://jakarta.ee/xml/ns/persistence https://jakarta.ee/xml/ns/persistence/persistence_3_0.xsd"
             version="3.0">
    <persistence-unit name="jpa-postgres">

        <class>models.Customer</class>
        <properties>
            <property name="jakarta.persistence.jdbc.driver" value="org.postgresql.Driver" />
            <property name="jakarta.persistence.jdbc.url" value="jdbc:postgresql://localhost:5432/filmland" />
            <property name="jakarta.persistence.jdbc.user" value="postgres" />
            <property name="jakarta.persistence.jdbc.password" value="root" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect" />
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.format_sql" value="true" />
            <property name="jakarta.persistence.schema-generation.database.action" value="create" />
        </properties>
    </persistence-unit>
</persistence>

因此，它应该使用与手动事务相同的“jpa-postgres”，sys outs 打印以下内容： 手动方法：

16:20:02,343 INFO  [stdout] (default task-1) Hibernate: 
16:20:02,343 INFO  [stdout] (default task-1)     select
16:20:02,343 INFO  [stdout] (default task-1)         c1_0.id,
16:20:02,343 INFO  [stdout] (default task-1)         c1_0.email,
16:20:02,343 INFO  [stdout] (default task-1)         c1_0.password 
16:20:02,344 INFO  [stdout] (default task-1)     from
16:20:02,344 INFO  [stdout] (default task-1)         customer c1_0
16:20:02,347 INFO  [stdout] (default task-1) Komt hier wel. Print evt entity manager: SessionImpl(394828776<open>)
16:20:02,348 INFO  [stdout] (default task-1) Komt hier wel. Print evt costumers: [Customer(id=1, [email protected], password=mooiman), Customer(id=2, [email protected], password=mooieding)]
16:20:02,348 INFO  [stdout] (default task-1) Komt hier wel. Print evt costumersDTO: [com.example.demo.dto.CustomerDto@52fb491a, com.example.demo.dto.CustomerDto@76e5d921]

@Transactional方法：

[2023-11-16 04:14:59,878] Artifact demo:war exploded: Deploy took 2,428 milliseconds
16:16:36,579 INFO  [stdout] (default task-1) Hibernate: 
16:16:36,579 INFO  [stdout] (default task-1)     select
16:16:36,579 INFO  [stdout] (default task-1)         c1_0.id,
16:16:36,580 INFO  [stdout] (default task-1)         c1_0.email,
16:16:36,580 INFO  [stdout] (default task-1)         c1_0.password 
16:16:36,580 INFO  [stdout] (default task-1)     from
16:16:36,580 INFO  [stdout] (default task-1)         customer c1_0
16:16:36,586 INFO  [stdout] (default task-1) Komt hier wel. Print evt entity manager: org.jboss.as.jpa.container.TransactionScopedEntityManager@2d71f100
16:16:36,587 INFO  [stdout] (default task-1) Komt hier wel. Print evt costumers: []
16:16:36,587 INFO  [stdout] (default task-1) Komt hier wel. Print evt costumersDTO: []

有人能够帮助我理解为什么会发生这种情况以及为什么我以错误的方式实现事务吗？