How can I use Spring Boot and Spring Data JPA to connect to multiple data sources?

Spring Boot, Spring Data JPA with Multiple DataSources

Spring Boot and Spring Data JPA can be used to connect to multiple data sources. To do this, you can use the @EnableJpaRepositories annotation to specify the base package for your repositories, and the @EnableTransactionManagement annotation to enable transaction management. You can then use the @Transactional annotation on your repository methods to specify which data source to use for each method.

For example, the following code shows how to configure Spring Boot to connect to two data sources:

<code class="java">@Configuration
@EnableJpaRepositories(
        entityManagerFactoryRef = "orderEntityManager",
        transactionManagerRef = "orderTransactionManager",
        basePackages = {"com.mm.repository.customer"})
public class CustomerDbConfig {

    @Bean(name = "customerEntityManager")
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(){
        // ...
    }

    // ...
}

@Configuration
@EnableJpaRepositories(
        entityManagerFactoryRef = "orderEntityManager",
        transactionManagerRef = "orderTransactionManager",
        basePackages = {"com.mm.repository.order"})
public class OrderDbConfig {

    @Bean(name = "orderEntityManager")
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(){
        // ...
    }

    // ...
}</code>

This code will create two EntityManagerFactory beans, one for each data source. The @Transactional annotation on the repository methods will then specify which EntityManagerFactory to use for each method. For example, the following code shows how to use the @Transactional annotation to specify that the findCustomer method should use the customerEntityManager bean:

<code class="java">@Repository
public interface CustomerRepository {

    @Transactional(value = "customerEntityManager")
    Customer findCustomer(Integer id);

    // ...
}</code>

Exceptions

If you are getting exceptions when trying to connect to multiple data sources, it is important to check the following:

• Ensure that the @EnableJpaRepositories and @EnableTransactionManagement annotations are present in your configuration classes.
• Ensure that the @Transactional annotation is present on your repository methods, and that it specifies the correct EntityManagerFactory bean to use.
• Inspect the exception message closely to determine what is causing the issue.

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