背景

最近公司要求支持国产数据库达梦，但达梦与PostgreSQL的语法有一些差异，需要做一些兼容操作。

操作步骤

本文采用dynamic-datasource-spring-boot-starter框架处理多数据源，多数据源配置如下

spring:
  datasource:
      dynamic:
        primary: dm #设置默认的数据源或者数据源组，默认值即为dm
        strict: false #设置严格模式，默认false不启动，启动后在未匹配到指定数据源时，会抛出异常，不启动则使用默认数据源
        datasource:
          mysql:
            driver-class-name: com.mysql.cj.jdbc.Driver
            url: jdbc:mysql://xxx.xx.xx.xx:3306/aco_sip?useUnicode=true&characterEncoding=UTF8&rewriteBatchedStatements=true&serverTimezone=PRC&useSSL=false&allowMultiQueries=true
            username: xxxxx
            password: xxxx

          pg:
            driver-class-name: org.postgresql.Driver
            url: jdbc:postgresql://xxx.xx.xx.xx:5432/aco_sip?currentSchema=aco_sip_dev
            username: xxxxx
            password: xxxxx

          dm:
            driver-class-name: dm.jdbc.driver.DmDriver
            url: jdbc:dm://xxx.xx.xx.xx:5236/aco_sip
            username: xxxxx
            password: xxxxxx

本文采用mybatis作为持久层框架，需要配置DatabaseIdProvider

// jreap.dbprovider.dbTypeStr=MySQL,DM,PostgreSQL
@Value("${jreap.dbprovider.dbTypeStr}")
private String dbProviderStr;

// 把支持的数据源设置到DatabaseIdProvider的properties中
@Bean
public DatabaseIdProvider getDatabaseIdProvider() {
    DatabaseIdProvider databaseIdProvider = new VendorDatabaseIdProvider();
    Properties properties = new Properties();
    if (!StringUtils.isEmpty(this.dbProviderStr)) {
        String[] dbProviderArr = this.dbProviderStr.split(",");

        for(int i = 0; i < dbProviderArr.length; ++i) {
            String dbType = dbProviderArr[i];
            if (!StringUtils.isEmpty(dbType)) {
                properties.setProperty(dbType, dbType.toLowerCase());
            }
        }
    }

    databaseIdProvider.setProperties(properties);
    return databaseIdProvider;
}

2.1 在SqlSessionFactoryBean#buildSqlSessionFactory中会判断容器中是否存在databaseIdProvider对象，如果存在则根据databaseIdProvider获取databaseId
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2.2 根据数据源的产品名在DatabaseIdProvider的properties中查找对应的value
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2.3 DynamicContext将databaseId设置到_databaseId参数中
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在xml中使用_databaseId参数对数据源进行区分

  <select id="queryPlayNumByHour" parameterType="Map" resultType="java.util.Map">
    <if test="_databaseId == 'mysql' 
        SELECT time,count(time) as num FROM
        ( SELECT id,concat(DATE_FORMAT(ea.alert_time,'HH' ),':00') AS time FROM play_his_record
        WHERE create_time BETWEEN #{startTime} and #{endTime} ) temp
        GROUP BY time ORDER BY time asc
    </if>
    <if test="_databaseId == 'postgresql' or _databaseId == 'dm'">
        SELECT time,count(time) as num FROM
        ( SELECT id,concat(to_char(create_time,'hh24'),':00') AS time FROM play_his_record
        WHERE create_time BETWEEN #{startTime} and #{endTime} ) temp
        GROUP BY time ORDER BY time asc
    </if>
</select>