mybatisplus3.5多数据源多数据库动态切换方言分页插件

环境：

    com.baomidou
    mybatis-plus-boot-starter
    3.5.2

  
     com.baomidou 
     dynamic-datasource-spring-boot-starter      3.4.0 
 

 官方提供的分页插件使用：

@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
    MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
    interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
    return interceptor;
}

 问题：mysql中支持limit ?,? ,而postgresql不支持limit ?,?。

解决方案：

1、默认使用

DbType.POSTGRE_SQL 可以解决。因为mysql兼容。

2、最佳方案： 使用空参PaginationInnerInterceptor插件类。如下：

public class DynamicPaginationInnerInterceptor extends PaginationInnerInterceptor {

}

public class MybatisPlusDynamicAutoConfig {
    public MybatisPlusDynamicAutoConfig() {
    }

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new DynamicPaginationInnerInterceptor());
        return interceptor;
    }
}

// 使用：
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@MapperScan("com.xxx.xxx.mapper")
public class MyBatisPlusConfig extends MybatisPlusDynamicAutoConfig {
}

牛逼

源码核心：

    /**
     * 获取分页方言类的逻辑
     *
     * @param executor Executor
     * @return 分页方言类
     */
    protected IDialect findIDialect(Executor executor) {
        if (dialect != null) {
            return dialect;
        }
        if (dbType != null) {
            dialect = DialectFactory.getDialect(dbType);
            return dialect;
        }
        return DialectFactory.getDialect(JdbcUtils.getDbType(executor));
    }


    /**
     * 不关闭 Connection,因为是从事务里获取的,sqlSession会负责关闭
     *
     * @param executor Executor
     * @return DbType
     */
    public static DbType getDbType(Executor executor) {
        try {
            Connection conn = executor.getTransaction().getConnection();
            return JDBC_DB_TYPE_CACHE.computeIfAbsent(conn.getMetaData().getURL(), JdbcUtils::getDbType);
        } catch (SQLException e) {
            throw ExceptionUtils.mpe(e);
        }
    }



    /**
     * 根据连接地址判断数据库类型
     *
     * @param jdbcUrl 连接地址
     * @return ignore
     */
    public static DbType getDbType(String jdbcUrl) {
        Assert.isFalse(StringUtils.isBlank(jdbcUrl), "Error: The jdbcUrl is Null, Cannot read database type");
        String url = jdbcUrl.toLowerCase();
        if (url.contains(":mysql:") || url.contains(":cobar:")) {
            return DbType.MYSQL;
        } else if (url.contains(":mariadb:")) {
            return DbType.MARIADB;
        } else if (url.contains(":oracle:")) {
            return DbType.ORACLE;
        } else if (url.contains(":sqlserver:") || url.contains(":microsoft:")) {
            return DbType.SQL_SERVER2005;
        } else if (url.contains(":sqlserver2012:")) {
            return DbType.SQL_SERVER;
        } else if (url.contains(":postgresql:")) {
            return DbType.POSTGRE_SQL;
        } else if (url.contains(":hsqldb:")) {
            return DbType.HSQL;
        } else if (url.contains(":db2:")) {
            return DbType.DB2;
        } else if (url.contains(":sqlite:")) {
            return DbType.SQLITE;
        } else if (url.contains(":h2:")) {
            return DbType.H2;
        } else if (regexFind(":dm\\d*:", url)) {
            return DbType.DM;
        } else if (url.contains(":xugu:")) {
            return DbType.XU_GU;
        } else if (regexFind(":kingbase\\d*:", url)) {
            return DbType.KINGBASE_ES;
        } else if (url.contains(":phoenix:")) {
            return DbType.PHOENIX;
        } else if (url.contains(":zenith:")) {
            return DbType.GAUSS;
        } else if (url.contains(":gbase:")) {
            return DbType.GBASE;
        } else if (url.contains(":gbasedbt-sqli:") || url.contains(":informix-sqli:")) {
            return DbType.GBASE_8S;
        } else if (url.contains(":clickhouse:")) {
            return DbType.CLICK_HOUSE;
        } else if (url.contains(":oscar:")) {
            return DbType.OSCAR;
        } else if (url.contains(":sybase:")) {
            return DbType.SYBASE;
        } else if (url.contains(":oceanbase:")) {
            return DbType.OCEAN_BASE;
        } else if (url.contains(":highgo:")) {
            return DbType.HIGH_GO;
        } else if (url.contains(":cubrid:")) {
            return DbType.CUBRID;
        } else if (url.contains(":goldilocks:")) {
            return DbType.GOLDILOCKS;
        } else if (url.contains(":csiidb:")) {
            return DbType.CSIIDB;
        } else if (url.contains(":sap:")) {
            return DbType.SAP_HANA;
        } else if (url.contains(":impala:")) {
            return DbType.IMPALA;
        } else if (url.contains(":vertica:")) {
            return DbType.VERTICA;
        } else if (url.contains(":xcloud:")) {
            return DbType.XCloud;
        } else if (url.contains(":firebirdsql:")) {
            return DbType.FIREBIRD;
        } else {
            logger.warn("The jdbcUrl is " + jdbcUrl + ", Mybatis Plus Cannot Read Database type or The Database's Not Supported!");
            return DbType.OTHER;
        }
    }

// 骚起来了～～～～