Coldfusion syntax - how to use Evaluate

Question

I'm trying to determine if a variable with a variable name is defined. Please help with my syntax... my attempts so far:

<cfif isDefined(Evaluate("session['#url.sessionSQL#']['SQL_ALL']"))>

<cfif isDefined('Evaluate("session[#url.sessionSQL#]")["SQL_ALL"]')>

<cfif isDefined(Evaluate("session['#url.sessionSQL#']['SQL_ALL']"))>        

<cfif isDefined('session[Evaluate("#url.sessionSQL#")]["SQL_ALL"]')>

<cfif isDefined('session["#url.sessionSQL#"]["SQL_ALL"]')>

Thanks.

Answer 1

Your question is a little confusing ;)

If session[url.sessionSQL]['SQL_ALL'] contains the name of a variable, you can use structKeyExists to verify that variable exists in a particular scope.

<cfif structKeyExists(scopeToCheck, "TestForThisVariableName")>  
... ie
<cfif structKeyExists(variables, session[url.sessionSQL].SQL_ALL)>

On the other hand, if just want to verify those session variables exist

  <cfif structKeyExists(session, url.sessionSQL) AND 
        structKeyExists(session[url.sessionSQL], "SQL_ALL")>

Either way, you do not need the evaluate() function.

Update: From comments, a key difference between IsDefined and StructKeyExists is precision. IsDefined examines a whole list of scopes when deteriming if a variable exists. Usually (though not always) that is undesirable because it can lead to unexpected results if you forget a particular variable exists in multiple scopes. (Using IsDefined inside a function is a prime example.) When you specifically want to check multiple scopes, then IsDefined() is more appropriate. Otherwise, I would stick with StructKeyExists as its results are less ambiguous.

Answer 2

Even though the answer below from Henry is best, I will point out the problem with your syntax above.

You want the string inside of isDefined() to be evaluated to a string but it is in quotes (which of course is required for isDefined() because it expects the name of a variable, not an actual variable. So you need hashmarks to make evaluate() run within the quotes.

<cfif isDefined('#Evaluate("session[url.sessionSQL]")#["SQL_ALL"]')>

Otherwise it is looking for a variable named "session[#url.sessionSQL#]")["SQL_ALL"]"

I did not actually test this, but I believe this should work. But clearly, the other way is MUCH better.

Answer 3

<cfif isDefined("#session[url.sessionSQL].SQL_ALL#")>

update

Assuming the name of the variable you want to check is stored in session[url.sessionSQL].SQL_ALL, but the pieces may not have been defined in url nor session nor in SQL_ALL

Then the safest version:

<cfif isDefined("url.sessionSQL") 
      and isDefined("session[url.sessionSQL]")
      and isDefined("session[url.sessionSQL].SQL_ALL")
      and isDefined("#session[url.sessionSQL].SQL_ALL#")>

Answer 4

EDIT:

As it turns out, Leigh's answer above works just fine, but not Henry's. In the interim, I found my own solution, as follows.

In the original question, I had a struct

"#session#"

which had an element referenced by a variable

"#url.sessionSQL#"

in other words,

"#session[sessionSQL]#" 

and I was trying to find whether that element had a structKey defined, named "SQL_ALL". I was able to make things work like so:

<cfset sessionSQL = #session[url.sessionSQL]# />
<cfif structKeyExists(sessionSQL, "SQL_ALL")>