How to use Coldfusion Components

[creole]

Okay...

I'm trying to improve my coding skills and practices so I'm looking into CFCs. It would be nice to split out my logic and my display.

I read over Ben Forta's article on how to use CFCs but it seems to be leaving some things out. For example, I've got a CFC that I built. All it does is to pull out the contents of a "page" in my database and display it.

I thought that this would be a simple thing to do to get started. It works when I hard code the page id into the CFC, but I want to be able to pass the page id from the page calling the component. Here's my CFC:

<cfcomponent hint="">

    <cffunction name="selectpage" hint="Selects page content from the database based on query string variable.">

        <cfquery name="getPageInformation" dataSource="#Application.DSN#" dbType="#Application.DBType#" username="#Application.username#" password="#Application.password#">

            SELECT *

            FROM tblpages

            WHERE page_id = '4';

        </cfquery>

        <cfoutput>#getPageInformation.page_content#</cfoutput>

    </cffunction>

</cfcomponent> 

Here's how I call it:

<cfinvoke component="getpages" method="selectpage" returnvariable="page" pageid="4"> 

You'll notice that I pass "pageid" into the component. But when I'm in the component, how do I access that argument? I tried this:
WHERE page_id = '#pageid#';

But it doesn't work. What am I doing wrong? Does someone have a good resource for this sort of thing? I really want to learn but nothing I've found on the web so far is really helpful. They all sort of assume that you know what CFCs are already.

[nagrom]

try:

WHERE page_id = '#arguments.pageid#'

you need them quotes? putting integers in a varchar fields, are we? tsk tsk

[creole]

No integers in varchar fields. I know better. I've found though that when I single quote the field, I don't get an error if for some ungodly reason the variable isn't there.

Actually, I found out what I needed, although your way might work as well. In the function, I defined an argument like so:
<cfargument name="pageid" type="numeric" required="true">

Works just fine. I'm going to try your way though. Seems silly to have to define an argument when I'm already passing on in. But, whatever works.

Tested your way and it works as well. I'll use that one instead. Thanks for your help.

[nagrom]

no problemo...

are you sure you're saving anything? if the query has to be run for every page, why not just put it Application.cfm ?

[Rynoguill]

Originally Posted by creole

<cfcomponent hint="">

    <cffunction name="selectpage" hint="Selects page content from the database based on query string variable.">

        <cfquery name="getPageInformation" dataSource="#Application.DSN#" dbType="#Application.DBType#" username="#Application.username#" password="#Application.password#">

            SELECT *

            FROM tblpages

            WHERE page_id = '4';

        </cfquery>

        <cfoutput>#getPageInformation.page_content#</cfoutput>

    </cffunction>

</cfcomponent> 

Here's how I call it:

<cfinvoke component="getpages" method="selectpage" returnvariable="page" pageid="4"> 

if i may, theres a few things you can do to make this a little easier, especially mentally. also it will fix your need to put things in quotes if there is no value.

try something more like this:

<cfcomponent hint="">
	<cffunction name="selectpage" hint="Selects page content from the database based on query string variable." output="true" returntype="query">
        <cfargument name="pageid" type="numeric" required="true">
		<cfquery name="getPageInformation" dataSource="#Application.DSN#" dbType="#Application.DBType#" username="#Application.username#" password="#Application.password#">
			SELECT *
			FROM tblpages
			WHERE page_id = #arguments.pageid#;
		</cfquery>
		<!---<cfoutput>#getPageInformation.page_content#</cfoutput>--->
         <cfreturn getpageinformation>
	</cffunction>
</cfcomponent>

and then call it like this...

  <cfinvoke 
	 component="(put the path to the component here, ask if you need help with this)"
	 method="selectpage"
	 returnvariable="selectpageret">
		<cfinvokeargument name="pageid" value="4"/>
	</cfinvoke>

by doing this you can do several things. first of all by adding the cfargument tag in the component you are requiring that the pageid is given and also that it is numeric. also, you are returning the query as output, so now you can use <cfoutput query="selectpageret"> on the actual page. it makes your code a lot more reusable, and now you can use it in different pages for different functions.

there are several other things you can do and reasons to do it with components, let me know and ill give some more examples. and let me know if you have any trouble with what ive put here

[r937]

has anybody done timings on components versus inline cfml?

all i can say is, for simplicity, i prefer this method

i save the query as getPageInformation.txt:

<cfquery name="getPageInformation" ... > 
   select foo, bar, quatsch 
     from tblpages 
    where page_id = #pageid# 
</cfquery>

and i invoke it like this:

<cfset pageid=4>
<cfinclude template="getPageInformation.txt">

and of course i can use <cfoutput query="getPageInformation">

i can use and reuse this cfquery anywhere, just as easily as that

what am i missing?

[Rynoguill]

Originally Posted by r937

i can use and reuse this cfquery anywhere, just as easily as that

what am i missing?

the main benifits to me with compents are:
reusability of code,
i only have to change things in my code in one place,
i can use them as webservices,
im an oop kinda guy,
i can do a lot of error checking,
it is really easy to use them on multiple sites, just a few changes to port them,
plus, its the wave of the future man!

and i havent noticed any performance differences, in fact if anything i feel like its faster or at least just as fast as inline code. and i have switch a couple older sites over to components.

just my two cents anyway...

[nagrom]

whelp,

r937 gets down with OPP?
insert into table e!?!?
yeah, you know me!
(bad joke, about bad music)

the real advantage to OOP is you can write functions that EXTEND other functions. uhhhh, inheritance is the word (i think).

but do typical websites require this level of abstraction? prolly not.

if you were working for a hospital, insurance company, or some other giant outfit with a complicated intranet and website you would certainly find situations.

but for simple stuff, i think it's overkill.

[davidjmedlock]

To be quite honest, I wish I could rewrite my companies entire application with CFMX using components. It's a large app that gets millions of hits a day and it desperately needs restructuring.

For my own websites, though, the only time I may use them is experimentally at first to see what they're like to use.

[creole]

Rudy...

While I'm not a great judge of speed, it seems to me as if the page loads faster after converting that inline code to a component. Sinec I'm using it in multiple places, it might be caching the bulk of the query.

[creole]

While I'm on components, here's another question.

I've got banner management built into this new site I'm working on:
http://997wtn.com.icglink.com

In the header I have two banner areas defined, top right (top right corner) and bottom left (under the nav buttons on the left).

I created another component to manage my banner queries; one function to get a random banner, and another function to update that banner's impression count. I would love to use this component in my header, just for consistencies sake but I've got an issue. I have two plain old inline queries right now, one query to get the top banner, and one to get the bottom. Then I have ONE update query which loops through those two banner ids and increments their impression.

How would I go about using components here? I've read that you can invoke the component using the cfobject tag, then CALL it using the cfinoke tag with a name attribute. But it doesn't seem to work.

So, rynogull or anyone else, can you guide me here? How can I use two calls to the same component, returning the same information, just with a different banner_id?


thanks

[Rynoguill]

straight from the coldfusion 6.1 documentation,

When to use CFCs
You can use CFCs in several ways:

To develop structured, reusable ColdFusion code
To create web services
To create elements that can be called by Flash clients
To create services that are accessed directly using a URL or form field
Developing structured, reusable code
Like other CFML code reuse techniques, such as user-defined functions (UDFs) and custom tags, components let you create application functionality that can be reused wherever you need it. If you want to modify, add, or remove component functionality, you make changes in only one component file.

Like UDFs and custom tags, CFCs provide an excellent method for developing structured applications that separate display elements from logical elements and encapsulate database queries.

CFCs have several advantages over UDFs and custom tags. The advantages include all the following "extras" that CFCs automatically provide. (Later sections describe these features in detail.)

The ability to group related functions into a single component, and to group related components into a package
Properties that can be shared by multiple functions
The This scope, a component-specific scope
Inheritance of component methods and properties from a base component, including the use of the Super keyword
Access control
Introspection into CFC functions, properties, and metadata
CFCs have one characteristic that prevents them from being the automatic choice for all code reuse: it takes substantially more processing time to instantiate a CFC than to process a custom tag (and it takes substantially more time to process a custom tag than to execute a user-defined function (UDF)). However, after a CFC is instantiated, calling a CFC method has about the same processing overhead as an equivalent custom tag. As a result, you should not use CFCs in place of independent, single-purpose, custom tags or UDFs. Instead, you should use CFCs to create bodies of related methods, particularly methods that share properties.

For more information about UDFs, custom tags, and other ColdFusion code reuse techniques, see Reusing Code in ColdFusion Pages.

so there you go, it does take more time to instaniate a cfc than a custom tag, but once it is instantiated its about the same. youre only going to notice this though on huge applications and cfc's, i have yet to notice it yet. to me, the ability to confine my code and only have to look one place to change it throughout my entire site. plus with the ability to do oop... i love it