我在用春季启动 2.X with 休眠5连接两个不同的 MySQL 数据库（Bar 和 Foo）在不同的服务器上。我试图列出一个实体的所有信息（自己的属性和@OneToMany and @ManyToOne关系）来自 REST 控制器中的方法。
我已经遵循了几个教程来做到这一点，因此，我能够获得我的所有信息@Primary数据库（Foo），但是，在检索辅助数据库（Bar）时，我总是会遇到异常@OneToMany套。如果我交换@Primary对 Bar 数据库进行注释，我能够从 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？
这是我得到的异常：
...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"])
我的应用程序属性：
# 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
My @Primary数据源配置：
@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);
}
}
我的辅助数据源配置：
@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);
}
实体为@Primary数据源。第二个数据源的实体是相同的（仅更改类名）：
@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);
}
}
值得注意的是，该解决方案应保留两个数据库的 Lazy 属性，以保持最佳性能。
Edit 1:如果两个目录（MySQL 术语中的“数据库”）位于同一个数据库（“服务器”）中，则 Rick James 解决方案有效！
问题依然存在当目录（MySQL 数据库）位于不同的数据库（服务器）中并且尝试保持 Lazy 属性时
非常感谢。
