4 Replies Latest reply on Mar 15, 2016 2:15 PM by WolfShade

    referencing dynamic field names

    dwright65 Level 1

      I'm having an issue testing a form field for a null condition.  The field names on the form are created dynamically as the form is created based on a query that returns a list of documents uploaded by a user. Each row will contain the document ID, document title and file name. As I loop through the query I create the form field name for each row by attaching the document ID to a string. Here is the code that creates the form:

      <cfform action="ec_process_attachment_upld.cfm"  method="post" enctype="multipart/form-data">  


      <cfif #get_attachment_list.RecordCount# GT 0>

             <table border="1">

             <cfloop query="get_attachment_list">

                   <cfset f_name = "upld_attachment_file" & #attachment_id#>



                 <td><input type="file" name="#f_name#" value=""></td>







      So, the field names generated will be upld_attachment_file1, upld_attachment_file2, etc.


      Here is the code that does the processing of the form:

      <cfloop query="get_attachment_info" >         

             <cfset f_name = "upld_attachment_file" & #attachment_id#>

             <cfset t_var = "form." & "#f_name#">


             <cfif len(#t_var#) GT 0>

                   Do stuff




      The query here is the same and the one that created form. As I loop through it, I'm again creating the field name on the fly. The problem comes in the CFIF statement when I try to test to see if the field is null or not. The test ends up testing the variable that hold the form field name rather than the form field itself. How can I test the form field?





        • 1. Re: referencing dynamic field names
          WolfShade Level 4

          Hi, dwright65,


          First of all, I'd like to point out that using hashmarks around variable names when not being directly output or not contained within strings can be detrimental - it actually might slow things down.


          <cfset f_name = "upld_attachment_file" & #attachment_id#>  should be <cfset f_name = "upld_attachment_file" & attachment_id />


          The best way to parse dynamic variable names is by using bracket notation.


          <cfif len(trim(form["upld_attachment_file#attachment_id#"]))><!--- You don't actually have to compare it to zero.  If the length is zero, it is false; if it's greater than zero, it's true --->
            DO STUFF


          In this second code sample, the hashmarks are required because the variable falls within a string.  It could also be written as


          <cfif len(trim(form["upld_attachment_file" & attachment_id]))>





          • 2. Re: referencing dynamic field names
            dwright65 Level 1

            Thanks! that worked like a charm. I also found that I could use the Evaluate function, but everything I read said not to use it unless absolutely necessary.

            • 3. Re: referencing dynamic field names
              Dave Ferguson Level 3

              You should never need to use evaluate.  Using the bracket notation as described by WolfShade  will work just fine in almost all conditions.

              • 4. Re: referencing dynamic field names
                WolfShade Level 4

                Thank you for marking my answer as correct, dwright65, I really appreciate it.


                And, as Dave Ferguson has pointed out, you should never use Evaluate() (for CF; or eval() in JavaScript) as it is not only dangerous (you're opening a window into a very sensitive, tender area of processing - interpreter/compiler), but it also will have a negative impact on performance.  When it comes to Eval[uate](), just say "NO!!!!!!!