String interpolation in scala not allowing selecting string from array

Question

So here is my code block

val cols = df.columns
val w = cols(0)
val query1  = s"select $cols(0), square(age) as age, age as age2, first_name, last_name from test"
val query2  = s"select $w, square(age) as age, age as age2, first_name, last_name from test"

Query 2 works just fine, query 1 throws the following error

no viable alternative at input 'select ['(line 1, pos 7)
== SQL ==
select [Ljava.lang.String;@7988d54(0), square(age) as age, age as age2, first_name, last_name from test

Is there anyway to accomplish query1 without creating a temp variable? I want to acces the indexed cols datatype directly.

I addressed your question directly but I just wanted to follow up after reading this again to tell you that if you're doing this as part of a SQL query, you're bypassing the safety of the JDBC driver. You're inviting SQL injection attacks. — wheaties
– wheaties, Commented Aug 23, 2018 at 18:49

wheaties · Accepted Answer · 2018-08-23 14:53:02Z

3

You can do it by nesting an expression within the string you're interpolating:

s"select ${col(0)} and then..."
s"select ${df.columns(0)} and then..."

You use the ${expr} to hold some expr which is valid code. The single variable version of the interpolation phrase $foo is actually short hand for ${foo}.

answered Aug 23, 2018 at 14:53

wheaties

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2 Comments

test acc Over a year ago

Do you have any recommendations on the proper way to do this without being vulnerable to injection? I am using this query with spark, so df = sqlContext.sql(query)

wheaties Over a year ago

Unfortunately, I can't give you a good recommendation as I have never used the SQL dataframe version. The JDBC drivers use prepared statements but I doubt there is the equivalent in Spark (I could be wrong.) There's probably a question on SO with the answer.

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