Sanitize user input with the USING keyword in PL/pgSQL

Question

This is how I create my search_term:

    IF char_length(search_term) > 0 THEN
        order_by := 'ts_rank_cd(textsearchable_index_col, to_tsquery(''' || search_term || ':*''))+GREATEST(0,(-1*EXTRACT(epoch FROM age(last_edited)/86400))+60)/60 DESC';
        search_term := 'to_tsquery(''' || search_term || ':*'') @@ textsearchable_index_col';
    ELSE
        search_term := 'true';
    END IF;

I am having some trouble with a PLPGSQL function:

    RETURN QUERY EXECUTE '
        SELECT
            *
        FROM
            articles
        WHERE
            $1 AND
            ' || publication_date_query || ' AND
            primary_category LIKE ''' || category_filter || ''' AND
            ' || tags_query || ' AND
            ' || districts_query || ' AND
            ' || capability_query || ' AND
            ' || push_notification_query || ' AND
            ' || distance_query || ' AND
            ' || revision_by || ' AND
            ' || publication_priority_query || ' AND
            ' || status_query || ' AND
            is_template = ' || only_templates || ' AND
            status <> ''DELETED''
        ORDER BY ' || order_by || ' LIMIT 500'
        USING search_term;
    END; $$;

returns ERROR:

argument of AND must be type boolean, not type text at character 64

As opposed to:

        RETURN QUERY EXECUTE '
            SELECT
                *
            FROM
                articles
            WHERE
                ' || search_term || ' AND
                ' || publication_date_query || ' AND
                primary_category LIKE ''' || category_filter || ''' AND
                ' || tags_query || ' AND
                ' || districts_query || ' AND
                ' || capability_query || ' AND
                ' || push_notification_query || ' AND
                ' || distance_query || ' AND
                ' || revision_by || ' AND
                ' || publication_priority_query || ' AND
                ' || status_query || ' AND
                is_template = ' || only_templates || ' AND
                status <> ''DELETED''
            ORDER BY ' || order_by || ' LIMIT 500';
        END; $$;

... which works. Am I missing something?
My goal is to sanitize my user input.

Answer 1

If some of your input parameters can be NULL or empty and should be ignored in this case, you best build your whole statement dynamically depending on user input - and omit respective WHERE / ORDER BY clauses completely.

The key is to handle NULL and empty string correctly, safely (and elegantly) in the process. For starters, search_term <> '' is a smarter test than char_length(search_term) > 0. See:

• Best way to check for "empty or null value"

And you need a firm understanding of PL/pgSQL, or you may be in over your head. Example code for your case:

CREATE OR REPLACE FUNCTION my_func(
         _search_term            text = NULL  -- default value NULL to allow short call
       , _publication_date_query date = NULL 
    -- , more parameters
       )
  RETURNS SETOF articles AS
$func$
DECLARE
   sql       text;
   sql_order text;   -- defaults to NULL

BEGIN
   sql := concat_ws(' AND '
    ,'SELECT * FROM articles WHERE status <> ''DELETED'''  -- first WHERE clause is immutable
    , CASE WHEN _search_term <> ''            THEN '$1 @@ textsearchable_index_col' END  -- ELSE NULL is implicit
    , CASE WHEN _publication_date_query <> '' THEN 'publication_date > $2'          END  -- or similar ...
 -- , more more parameters
   );

   IF search_term <> '' THEN  -- note use of $1!
      sql_order  := 'ORDER BY ts_rank_cd(textsearchable_index_col, $1) + GREATEST(0,(-1*EXTRACT(epoch FROM age(last_edited)/86400))+60)/60 DESC';
   END IF;

   RETURN QUERY EXECUTE concat_ws(' ', sql, sql_order, 'LIMIT 500')
   USING  to_tsquery(_search_term || ':*')  -- $1  -- prepare ts_query once here!
        , _publication_date_query           -- $2  -- order of params must match!
     -- , more parameters
   ;

END
$func$  LANGUAGE plpgsql;

I added default values for function parameters, so you can omit params that don't apply in the call. Like:

SELECT * FROM my_func(_publication_date_query => '2016-01-01');

More:

• Functions with variable number of input parameters
• The forgotten assignment operator "=" and the commonplace ":="

Note the strategic use of concat_ws(). See:

• How to concatenate columns in a Postgres SELECT?

Here is a related answer with lots of explanation:

• Test for null in function with varying parameters