Question

I am trying to write a session helper and facing to problem to test if a Struct key in session exists?

I am trying like

<cffunction name="Exists" access="public" output="false" returntype="boolean" >
    <cfargument name="Key" required="true" type="Any" />
    <cfreturn Evaluate( "StructKeyExists( Session, #Arguments.Key# )" ) />
</cffunction>

Where I am calling the function like

<cfif Exists("data.fromdate") >
 ...
</cfif>

How should I write it?

Thanks

Answer 1

The following code will check any depth struct, and also correctly locks the Session scope.

<cffunction name="Exists" access="public" output="false" returntype="boolean">
    <cfargument name="Key" required="true" type="string">

    <cfset local.mainKeyList = ListChangeDelims(ListDeleteAt(Arguments.Key, ListLen(Arguments.Key, "."), "."), ",", ".")>

    <cfset local.StructChain = "Session">
    <cfloop list="#local.mainKeyList#" index="local.CurrentKey">
        <cfset local.StructChain &= '["#local.CurrentKey#"]'>
    </cfloop>

    <cflock scope="session" type="readonly" timeout="3">
        <cftry>
            <cfset local.Exists = StructKeyExists(Evaluate(local.StructChain), ListLast(Arguments.Key, "."))>

            <cfcatch>
                <cfset local.Exists = false>
            </cfcatch>
        </cftry>
    </cflock>

    <cfreturn local.Exists>
</cffunction>

<cflock scope="session" type="exclusive" timeout="3">
    <cfset Session.data.log.deep = "I'm here!">
</cflock>
<cfoutput>#Exists("data.log.deep")#</cfoutput>

Hopefully the amount of code in this function will justify why a helper function would be useful, to those pondering your reasons. This doesn’t currently, but could be enhanced to, deal with Structs inside of Arrays as well. This also doesn’t deal with an empty Arguments.Key, or fail gracefully on a cflock timeout, but should get you started.

Additionally, those that want to comment that cflock isn’t required, please read the ColdFusion cflock docs first.

Simplified, but may provide inaccurate results in extremely rare conditions

Doing an IsDefined inline in your code will provide the opportunity for false positives, however having the IsDefined inside a udf or cfc method reduces this risk greatly to the point it may not need be a consideration. If you’re happy to take that chance then you can simplify the function using IsDefined as Peter Boughton suggests.

<cffunction name="Exists" access="public" output="false" returntype="boolean">
    <cfargument name="Key" required="true" type="string">

    <cflock scope="session" type="readonly" timeout="3">
        <cfset local.Exists = IsDefined("Session." & Arguments.Key)>
    </cflock>

    <cfreturn local.Exists>
</cffunction>