Spring Data JPA 多數據源+異構數據庫實踐

有個項目須要做SQL Server到MySQL的數據遷移，並且兩邊的schema也有很多差別，這時候用工具去遷移就很難了，須要寫程序去控制每一個字段的變換。因而採用Spring Data JPA來作這件事，自動搞定各類DAO，並且底層的Hibernate也輕鬆支持SQL Server和MySQL的

作這個事情的第一步就是配置兩個數據源，一個連MySQL，一個連SQL Server。不少須要支持讀寫分離多數據源的和這個相似，只會更簡單，由於只用支持MySQL就能夠。下面看代碼：

配置文件

application.yml的內容是：

spring:
  datasource:
    mssql:
      type: org.apache.tomcat.jdbc.pool.DataSource
      driver-class-name: com.microsoft.sqlserver.jdbc.SQLServerDriver
      url: jdbc:sqlserver://localhost:1433;database=old;
      username: sa
      password: password
    mysql:
      type: org.apache.tomcat.jdbc.pool.DataSource
      driver-class-name: com.mysql.jdbc.Driver
      url: jdbc:mysql://localhost:3306/new?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&zeroDateTimeBehavior=convertToNull&useSSL=false
      username: root
      password: password
  jpa:
    show-sql: false

能夠看到，很清楚的兩個數據源配置，下面來看怎樣使用這兩個配置

DataSource配置類

import org.springframework.boot.autoconfigure.jdbc.DataSourceBuilder;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.transaction.PlatformTransactionManager;

import javax.sql.DataSource;
import java.util.Properties;

@Configuration
public class DataSourceConfiguration {

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

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

    @Bean(name = "mssqlEntityManagerFactory")
    @Primary
    public LocalContainerEntityManagerFactoryBean mssqlEntityManagerFactory(
            EntityManagerFactoryBuilder builder) {
        LocalContainerEntityManagerFactoryBean em = builder
                .dataSource(mssqlDataSource())
                .packages(OldBuy.class)
                .persistenceUnit("mssql")
                .build();
        Properties properties = new Properties();
        properties.setProperty("hibernate.physical_naming_strategy", "org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl");
        em.setJpaProperties(properties);
        return em;
    }

    @Bean(name = "mysqlEntityManagerFactory")
    public LocalContainerEntityManagerFactoryBean mysqlEntityManagerFactory(
            EntityManagerFactoryBuilder builder) {
        LocalContainerEntityManagerFactoryBean em = builder
                .dataSource(mysqlDataSource())
                .packages(Buy.class)
                .persistenceUnit("mysql")
                .build();
        Properties properties = new Properties();
        properties.setProperty("hibernate.physical_naming_strategy", "org.springframework.boot.orm.jpa.hibernate.SpringPhysicalNamingStrategy");
        em.setJpaProperties(properties);
        return em;
    }

    @Bean(name = "mssqlTransactionManager")
    @Primary
    PlatformTransactionManager mssqlTransactionManager(EntityManagerFactoryBuilder builder) {
        return new JpaTransactionManager(mssqlEntityManagerFactory(builder).getObject());
    }

    @Bean(name = "mysqlTransactionManager")
    @Primary
    PlatformTransactionManager mysqlTransactionManager(EntityManagerFactoryBuilder builder) {
        return new JpaTransactionManager(mysqlEntityManagerFactory(builder).getObject());
    }
}

這裏主要分三塊：

1. 最上面的兩個DataSource類，根據配置文件產生數據源，注意必須一個是Primary的，否則Spring會報錯，由於找到了bean的兩個實現，默認不知道選哪一個

2. 中間的兩個LocalContainerEntityManagerFactoryBean則是根據兩個數據源產生對應的EntityManager，這裏就能夠作些hibernate的特定配置了，好比取名策略、sql方言之類的

3. 最後兩個PlatformTransactionManager則是根據兩個EntityManager產生對應的事務管理器，這樣咱們才能用事務

Repository配置

如今萬事俱備，只欠東風了，也就是指定咱們哪些Repository用上面配置好的兩套DataSource、EntityManager、Transaction Manager：

SQL Server配置

import org.springframework.context.annotation.Configuration;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.transaction.annotation.EnableTransactionManagement;

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(
        basePackageClasses = MsSQLXXXRepository.class,
        entityManagerFactoryRef = "mssqlEntityManagerFactory",
        transactionManagerRef = "mssqlTransactionManager"
)
public class MssqlConfiguration {
}

MySQL配置

import org.springframework.context.annotation.Configuration;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.transaction.annotation.EnableTransactionManagement;

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(
        basePackageClasses = MySQLYYYRepository.class,
        entityManagerFactoryRef = "mysqlEntityManagerFactory",
        transactionManagerRef = "mysqlTransactionManager"
)
public class MysqlConfiguration {
}

上面就是兩種Repository的配置了，很簡單。basePackageClasses指向的那個類，同一個包裏面的全部Repository都會用這個數據源的配置