只读副本和Spring Data第3部分：配置两个实体管理器

我们之前的设置可以正常工作。我们现在要做的是进一步发展，并配置两个单独的实体管理器，而不会影响我们之前实现的功能。

第一步是将默认的实体管理器配置设置为主要配置。
这是第一步

 package com.gkatzioura.springdatareadreplica.config;  import javax.sql.DataSource;  import org.springframework.beans.factory.annotation.Qualifier;  import org.springframework.beans.factory.annotation.Value;  import org.springframework.boot.jdbc.DataSourceBuilder;  import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;  import org.springframework.context.annotation.Bean;  import org.springframework.context.annotation.ComponentScan;  import org.springframework.context.annotation.Configuration;  import org.springframework.context.annotation.Primary;  import org.springframework.data.jpa.repository.config.EnableJpaRepositories;  import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;  @Configuration  public class PrimaryEntityManagerConfiguration { @Value ( "${spring.datasource.username}" ) private String username; @Value ( "${spring.datasource.password}" ) private String password; @Value ( "${spring.datasource.url}" ) private String url; @Bean @Primary public DataSource dataSource() throws Exception { return DataSourceBuilder.create() .url(url) .username(username) .password(password) .driverClassName( "org.postgresql.Driver" ) .build(); } @Bean @Primary public LocalContainerEntityManagerFactoryBean entityManagerFactory( EntityManagerFactoryBuilder builder, @Qualifier ( "dataSource" ) DataSource dataSource) { return builder.dataSource(dataSource) .packages( "com.gkatzioura.springdatareadreplica" ) .persistenceUnit( "main" ) .build(); }  }

如果您使用此配置运行您的应用程序，它将像之前的应用程序一样运行。
现在是时候配置只读实体管理器了。

 package com.gkatzioura.springdatareadreplica.config;  import javax.sql.DataSource;  import org.springframework.beans.factory.annotation.Qualifier;  import org.springframework.beans.factory.annotation.Value;  import org.springframework.boot.jdbc.DataSourceBuilder;  import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;  import org.springframework.context.annotation.Bean;  import org.springframework.context.annotation.Primary;  import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;  @Configuration  public class ReadOnlyEntityManagerConfiguration { @Value ( "${spring.datasource.username}" ) private String username; @Value ( "${spring.datasource.password}" ) private String password; @Value ( "${spring.datasource.readUrl}" ) private String readUrl; @Bean public DataSource readDataSource() throws Exception { return DataSourceBuilder.create() .url(readUrl) .username(username) .password(password) .driverClassName( "org.postgresql.Driver" ) .build(); } @Bean public LocalContainerEntityManagerFactoryBean readEntityManagerFactory( EntityManagerFactoryBuilder builder, @Qualifier ( "readDataSource" ) DataSource dataSource) { return builder.dataSource(dataSource) .packages( "com.gkatzioura.springdatareadreplica" ) .persistenceUnit( "read" ) .build(); }  }

另外，我将向控制器添加方法以保存模型。

 package com.gkatzioura.springdatareadreplica.controller;  import java.util.List;  import org.springframework.http.HttpStatus;  import org.springframework.web.bind.annotation.GetMapping;  import org.springframework.web.bind.annotation.PostMapping;  import org.springframework.web.bind.annotation.RequestBody;  import org.springframework.web.bind.annotation.ResponseStatus;  import org.springframework.web.bind.annotation.RestController;  import com.gkatzioura.springdatareadreplica.entity.Employee;  import com.gkatzioura.springdatareadreplica.repository.EmployeeRepository;  @RestController  public class EmployeeContoller { private final EmployeeRepository employeeRepository; public EmployeeContoller(EmployeeRepository employeeRepository) { this .employeeRepository = employeeRepository; } @GetMapping ( "/employee" ) public List<Employee> getEmployees() { return employeeRepository.findAll(); } @PostMapping ( "/employee" ) @ResponseStatus (HttpStatus.CREATED) @ResponseStatus (HttpStatus.CREATED) public void addEmployee( @RequestBody Employee employee) { employeeRepository.save(employee); }  }

如果您确实尝试使用控制器添加员工，然后查询读取的数据库，您将看到根本没有添加任何条目。

因此，我们已经启动并运行了主要的实体管理器，而我们也有辅助的实体管理器。第二个尚未使用。下一个博客着重于使用辅助只读实体管理器。