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This guide shows how to configure multiple Derby databases in a Spring Boot project for handling different data sources.

1. Add Dependencies

In pom.xml: 
<dependency>
  <groupId>org.apache.derby</groupId>
  <artifactId>derby</artifactId>
  <scope>runtime</scope>
</dependency>

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

2. Configure Multiple Data Sources

In application.properties: 
# First database
spring.datasource.primary.url=jdbc:derby:/app/data/db1;create=true
spring.datasource.primary.driver-class-name=org.apache.derby.jdbc.EmbeddedDriver
spring.datasource.primary.username=sa
spring.datasource.primary.password=

# Second database
spring.datasource.secondary.url=jdbc:derby:/app/data/db2;create=true
spring.datasource.secondary.driver-class-name=org.apache.derby.jdbc.EmbeddedDriver
spring.datasource.secondary.username=sa
spring.datasource.secondary.password=

3. Create Config for Primary Database

import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.*;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.*;
import javax.sql.DataSource;

@Configuration
@EnableJpaRepositories(
    basePackages = "com.example.repo.primary",
    entityManagerFactoryRef = "primaryEntityManager",
    transactionManagerRef = "primaryTxManager"
)
public class PrimaryConfig {

    @Bean
    @Primary
    public LocalContainerEntityManagerFactoryBean primaryEntityManager(
            EntityManagerFactoryBuilder builder, DataSource dataSource) {
        return builder.dataSource(dataSource)
                .packages("com.example.model.primary")
                .persistenceUnit("primary").build();
    }

    @Bean
    @Primary
    public JpaTransactionManager primaryTxManager(
            LocalContainerEntityManagerFactoryBean primaryEntityManager) {
        return new JpaTransactionManager(primaryEntityManager.getObject());
    }
}

4. Create Config for Secondary Database

@Configuration
@EnableJpaRepositories(
    basePackages = "com.example.repo.secondary",
    entityManagerFactoryRef = "secondaryEntityManager",
    transactionManagerRef = "secondaryTxManager"
)
public class SecondaryConfig {

    @Bean
    public LocalContainerEntityManagerFactoryBean secondaryEntityManager(
            EntityManagerFactoryBuilder builder, DataSource dataSource) {
        return builder.dataSource(dataSource)
                .packages("com.example.model.secondary")
                .persistenceUnit("secondary").build();
    }

    @Bean
    public JpaTransactionManager secondaryTxManager(
            LocalContainerEntityManagerFactoryBean secondaryEntityManager) {
        return new JpaTransactionManager(secondaryEntityManager.getObject());
    }
}

5. Create Entities

  • com.example.model.primary.User
  • com.example.model.secondary.Order
Each mapped to its own repository package.

6. Test Multiple Connections

@RestController
@RequestMapping("/multi")
public class MultiController {
    private final UserRepository userRepo;
    private final OrderRepository orderRepo;

    public MultiController(UserRepository userRepo, OrderRepository orderRepo) {
        this.userRepo = userRepo;
        this.orderRepo = orderRepo;
    }

    @PostMapping("/user")
    public User addUser(@RequestBody User u) {
        return userRepo.save(u);
    }

    @PostMapping("/order")
    public Order addOrder(@RequestBody Order o) {
        return orderRepo.save(o);
    }
}

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