Scala字符串变量替换 [英] Scala String Variable Substitution

问题描述

我有用Scala编写的Spark代码. Spark读取存储要执行的SQL的元表(已经在spark中作为临时表).

I have spark code written in scala. Spark Reads meta tables (already in spark as temp table) which stores the SQL to be executed.

我面临的问题是我们有使用变量(在scala代码中定义)的查询

Problem I am facing is that we have queries which uses variables (defined in scala code)

我尝试了不同的方法，但无法用值替代变量.

I tried different methods but I am not able to substitute variable with value.

var begindate= s"2017-01-01";
var enddate =  s"2017-01-05";

Msg.print_info(s"begin processing from ${beginDate} to ${endDate}");


//Reading SQL from MetaData table stored in spark as meta_table (temp table)

val dynamic_read_sql = s"""
        select SQL_TEXT
        from meta_table""";

val dynamic_sql_query = sqlContext.sql(dynamic_read_sql);
val check_query = dynamic_sql_query.first().getString(0);

Msg.print_info(s"check_query = $check_query");

我正在正确显示sql.

I am geting sql displayed correctly.

// date is also temp table in spark
select * from date where load_date >= '${begindate}' and load_date <='${enddate}'

下一步是执行此sql

Next step is to execute this sql

dynamic_sql_find = sqlContext.sql(check_query);

但是它无法替换代码中已经定义的'$ {begindate}'和'$ {enddate}'.因此，返回0条记录.

But it fails to replace '${begindate}' and '${enddate}' which are already defined in code. Hence, returns 0 records.

我试图将商店存储在另一个变量中.

I tried to store the store in another variable.

val replace_check_query = s"${check_query}"

但是，它没有替换变量.

But, It did not replace the variable.

可以请您帮忙吗?

推荐答案

正如@radumanolescu正确地说的那样，begindate和enddate仅在编译时被替换.要在运行时替换这些字符串，您可以手动替换子字符串:

As @radumanolescu correctly said, begindate and enddate are substituted only at compile time. To substitute these at runtime you can replace substrings manually:

val dynamic_sql_query = sqlContext.sql(check_query).replace("${begindate}", begindate).replace("${enddate}", enddate)

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