如何配置Spring启动以使用两个数据库？

Question

我使用Spring Boot 2.X和Hibernate 5 在不同的服务器上连接两个不同的MySQL数据库(Bar和Foo).我试图从REST控制器中的方法列出实体的所有信息(自己的属性@OneToMany和@ManyToOne关系).

我已经按照几个教程来执行此操作,因此,我能够获取我的@Primary数据库(Foo)的所有信息,但是,在检索@OneToMany集合时,我总是得到我的辅助数据库(Bar)的例外.如果我将@Primary注释交换到Bar数据库,我可以从Bar数据库获取数据,但不能从Foo数据库获取数据.有办法解决这个问题吗？

这是我得到的例外:

...w.s.m.s.DefaultHandlerExceptionResolver :
Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException: 
    Could not write JSON document: failed to lazily initialize a collection of role: 
        com.foobar.bar.domain.Bar.manyBars, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]-com.foobar.bar.domain.Bar["manyBars"]); 
    nested exception is com.fasterxml.jackson.databind.JsonMappingException:
        failed to lazily initialize a collection of role: 
        com.foobar.bar.domain.Bar.manyBars, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.foobar.bar.domain.Bar["manyBars"])

我的application.properties:

# MySQL DB - "foo"
spring.datasource.url=jdbc:mysql://XXX:3306/foo?currentSchema=public
spring.datasource.username=XXX
spring.datasource.password=XXX
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
# MySQL DB - "bar"
bar.datasource.url=jdbc:mysql://YYYY:3306/bar?currentSchema=public
bar.datasource.username=YYYY
bar.datasource.password=YYYY
bar.datasource.driver-class-name=com.mysql.jdbc.Driver
# JPA
spring.jpa.show-sql=true
spring.jpa.hibernate.ddl-auto=none
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5Dialect

我的@PrimaryDataSource配置:

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(entityManagerFactoryRef = "entityManagerFactory",
        transactionManagerRef = "transactionManager",
        basePackages = {"com.foobar.foo.repo"})
public class FooDbConfig {

    @Primary
    @Bean(name = "dataSource")
    @ConfigurationProperties(prefix = "spring.datasource")
    public DataSource dataSource() {
        return DataSourceBuilder.create().build();
    }

    @Primary
    @Bean(name = "entityManagerFactory")
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(
            EntityManagerFactoryBuilder builder, @Qualifier("dataSource") DataSource dataSource) {
        return builder
                .dataSource(dataSource)
                .packages("com.foobar.foo.domain")
                .persistenceUnit("foo")
                .build();
    }

    @Primary
    @Bean(name = "transactionManager")
    public PlatformTransactionManager transactionManager(
            @Qualifier("entityManagerFactory") EntityManagerFactory entityManagerFactory) {
        return new JpaTransactionManager(entityManagerFactory);
    }
}

我的辅助DataSource配置:

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(entityManagerFactoryRef = "barEntityManagerFactory",
        transactionManagerRef = "barTransactionManager", basePackages = {"com.foobar.bar.repo"})
public class BarDbConfig {

    @Bean(name = "barDataSource")
    @ConfigurationProperties(prefix = "bar.datasource")
    public DataSource dataSource() {
        return DataSourceBuilder.create().build();
    }

    @Bean(name = "barEntityManagerFactory")
    public LocalContainerEntityManagerFactoryBean barEntityManagerFactory(
            EntityManagerFactoryBuilder builder, @Qualifier("barDataSource") DataSource dataSource) {
        return builder
                .dataSource(dataSource)
                .packages("com.foobar.bar.domain")
                .persistenceUnit("bar")
                .build();
    }

    @Bean(name = "barTransactionManager")
    public PlatformTransactionManager barTransactionManager(
            @Qualifier("barEntityManagerFactory") EntityManagerFactory barEntityManagerFactory) {
        return new JpaTransactionManager(barEntityManagerFactory);
    }
}

REST控制器类:

@RestController
public class FooBarController {

    private final FooRepository fooRepo;
    private final BarRepository barRepo;

    @Autowired
    FooBarController(FooRepository fooRepo, BarRepository barRepo) {
        this.fooRepo = fooRepo;
        this.barRepo = barRepo;
    }

    @RequestMapping("/foo")
    public List<Foo> listFoo() {
        return fooRepo.findAll();
    }

    @RequestMapping("/bar")
    public List<Bar> listBar() {
        return barRepo.findAll();
    }

    @RequestMapping("/foobar/{id}")
    public String fooBar(@PathVariable("id") Integer id) {
        Foo foo = fooRepo.findById(id);
        Bar bar = barRepo.findById(id);

        return foo.getName() + " " + bar.getName() + "!";
    }

}

Foo/Bar存储库:

@Repository
public interface FooRepository extends JpaRepository<Foo, Long> {
  Foo findById(Integer id);
}

@Repository
public interface BarRepository extends JpaRepository<Bar, Long> {
  Bar findById(Integer id);
}

@Primary数据源的实体.第二个数据源的实体是相同的(只更改类名):

@Entity
@Table(name = "foo")
public class Foo {

    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "id", unique = true, nullable = false)
    private Integer id;

    @Column(name = "name")
    private String name;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "foo")
    @JsonIgnoreProperties({"foo"})
    private Set<ManyFoo> manyFoos = new HashSet<>(0);

    // Constructors, Getters, Setters
}

@Entity
@Table(name = "many_foo")
public class ManyFoo {

    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "id", unique = true, nullable = false)
    private Integer id;

    @Column(name = "name")
    private String name;

    @ManyToOne(fetch = FetchType.LAZY)
    @JsonIgnoreProperties({"manyFoos"})
    private Foo foo;

    // Constructors, Getters, Setters
}  

最后,我的应用程序主要:

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

重要的是要注意解决方案应保留两个数据库的Lazy属性,以保持最佳性能.

编辑1:如果两个目录(MySQL术语中的"数据库")在同一个数据库("服务器")中,那么Rick James解决方案就可以运行!!

当目录(MySQL数据库)位于不同的数据库(服务器)中并且尝试将Lazy保留为属性时,问题仍然存在

非常感谢.

Answer 1

*默认情况下,ToMany Collections在Hibernate和JPA中是惰性的.错误是因为当实体管理器(也就是hibernate-speak中的会话)关闭时,Jackson正在尝试序列化OneToMany.因此,无法检索惰性集合.

默认情况下,带JPA的Spring Boot OpenEntityManagerInViewFilter为主EM提供.这允许只读数据库访问,但默认情况下仅适用于主EM.

你有3个选择:

1)您可以添加连接提取,例如FetchMode如何在Spring Data JPA中工作

2)您可以为非主要实体管理器添加OpenEntityManagerInViewFilter并将其添加到您的上下文中.

请注意,这意味着挑战,对于每个Bar和Foo实例,您的应用程序将返回数据库以检索OneToMany.这是不适用于Bar的部分,但适用于Foo.这意味着一个可伸缩性问题(一些人称之为N + 1问题),对于每个foo和bar,你运行一个额外的查询,这对于非平凡数量的Foos和Bars来说会变慢.

3)另一种方法是让你的收藏品在Bar and Foo eager上看到(请参阅https://docs.oracle.com/javaee/7/api/javax/persistence/OneToMany.html#fetch--)但这需要是仔细分析是否可扩展性对您来说是一个问题.

我建议选项#1.