Recently I was assigned a new client that uses mostly ColdFusion 9 for their applications. In the past the majority of my clients have not taken the opportunity to upgrade from version 8, and there has not really been much reason to that I’ve run into as well. However, this opportunity creates the needed effort to make sure I know the differences between 8 and 9, such as var scoping.

As you probably know the variables scope in a CFC is private to that CFC. In other words the object calling that component may not access this scope’s values until it is returned to it. This scope can be set using the “variables” prefix to the variable name. If you skip the scope, it will be assigned to the variables scope. The following code sets the same variable and will persist between calls to each method the component contains.

<cffunction>
    <cfset variables.var1 = "Example 1">
    <cfset var1 = "Example 2">
    <!--- resulting in both variables.var1 and var1 values set to "Example 2" --->
</cffunction>

Normally you would want to declare variables private to each method so that your values are never overwritten by other process. This is normally done by using the var keyword. However in ColdFusion 9 you may use the local scope instead. This local scope does not persist between calls to the component’s methods. For example the following two lines work the same (the var keyword would not be required in this instance if using CF9):

<cffunction>
    <cfset var var1="Example 1">
    <cfset local.var1="Example 2">
    <cfreturn local.var1> <!--- Returns "Example 2", returning var1 would result in an error as it does not exist --->
</cffunction>

The question now becomes “What if I var scoped a local struct to use in previous versions of ColdFusion (var local={})?” The answer is you are good to go. ColdFusion 9 will just create a struct named “local” in the local scope (local.local).  So if you are coding for CF9 there is no reason to var scope a local struct as you would just be creating an unused struct. Instead use the already existent local scope. But you don’t need to go back and re-factor your code to remove all the local var scopes as an empty struct will not cause any harm unless you where counting on local.local to be there in the past. The following example is backwards compatible in CF9.

<cffunction>
    <cfset var local = {}> <!--- In CF9 this will result in local.local, so leave this out --->
    <cfset local.var1 = "Example1">
    <cfreturn local.var1>
</cffunction>

If you use JDBC drivers for your ODBC source in ColdFusion, you may notice that you don’t return a new column entered into your database table using SELECT *. You may also get an error such as “Syntax error converting the varchar value ‘billboard’ to a column of data type int”.

I’ve known about this for awhile from Mark Kruger, but other people have asked me about this nuance.

Basically when you use SELECT * in your query, it caches the database schema.

Example Code:

<cfquery name="q1" datasource="#application.DSN#">
SELECT * FROM TABLE1
WHERE COLA = <cfqueryparam cfsqltype="CF_SQL_VARCHAR" value="A">
</cfquery>

Three things can fix this:

1. Update your code to include the specific column names, such as “SELECT COLA, COLB”. This will also increase performance since SQL doesn’t have to lookup the table columns.
2. Change your query somehow, even adding a space
3. Restart the ColdFusion Service. This will flush out the schema cache.