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Node Routes with Functional Programming

Today’s post is a little short and a little late as I’m pretty busy at work!

I’m going to do a quick functional programming example that I do in my routing of my application, now there probably is an easier way, but as allways programming is a process.

Here’s the code:

_boolHandle = (_f) -> (req, res) ->
  _testExists req.params.ticketID, res, -></pre>
    _f req, res, (err, results) -> if err then res.status(500).json err else res.status(200).json results or true
app.post '/api/ticket/:ticketID/metadata', _boolHandle (req, res, cb) -> $tickets.metadata req.params.ticketID, req.body, cb

This is essentially a post handler in express 4 that calls a function that returns a function to call a function to call a standard response!

If we break it down, when we register the handler, normally this would be written as follows:


app.post '/api/ticket/:ticketID/metadata', (req, res) -> res.status(200).json true

My first step was figuring out that every call I made to the $ticket object calls it’s callback with (err, result) and returned the results, so my code then looks like this:


app.post '/api/ticket/:ticketID/metadata', (req, res) -> $ticket.metadata req.params.ticketID, (err, result) -> if err then res.status(500).json err else res.status(200).json result

Because I’m lazy I decided I didn’t want to write out the callback every time, it’s always the same so why bother? So my first functional programming block was this:

_boolHandle = (_f) -> (req, res) ->
  _f req, res, (err, results) -> if err then res.status(500).json err else res.status(200).json results or true
app.post '/api/ticket/:ticketID/metadata', _boolHandle (req, res, cb) -> $tickets.metadata req.params.ticketID, cb

As you can see I abstracted out the response by creating a wrapper around it. The other part I have in the code is the function that tests whether the ticketID actually exists (_testExists), if it exists it calls the callback else it returns a “ticket not found” error.

I hope this explanation helps someone out, if you have a better way of doing this – I’m all ears!!

Why I’ve come to love functional programming

Recently I have been starting to learn Node.js and inadvertently changed my opinion of functional programming VS Object Oriented programming. During my work on supporting legacy Coldfusion sites I stumbled across some code that forms the basis of this comparison of functional programming VS Object Oriented programming. (PS if you want a good introduction to the differences look on over to: http://steve-yegge.blogspot.com/2006/03/execution-in-kingdom-of-nouns.html).

This particular example will be Coldfusion and Pseudo-javascript (or coffeescript) and focuses around a multi-keyword search on 3 columns on 2 tables. Our tables are as follows:

Table Name: Jedi
With Columns: Name, Planet, Lightsaber_Colour.

Table Name: Sith
With Columns: Name, Catch_Phrase, Teacher.

First of all we will define a master function, and a convenience function for searching each of the tables, we do this for an attempt at reusability. We’ll call this main search function “galacticSearch” which will return a SQL string and take the arguments: Keyword (required, string), table (required, string) and andFlag (optional, boolean, defaults to true). The andFlag determines whether our search will return with all the keywords or any of the keywords (AND and OR searches respectively). The SQL returned will be less than perfect as really we should use something more forgiving and inclusive than the ‘=’ operator, for example in MSSQL name LIKE “%#ListGetAt(arguments.keywords, i, ‘ ‘)#%”. Also the params should be using cfqueryparam etc etc, it’s not perfect code but it doesn’t have to be production code for illustration purposes!

Here’s my implementation in Coldfusion, standing up for the Object Oriented languages:

<cffunction name="jediSearch" returnType="string">
	<cfargument name="keywords" required="true" required="false" type="string">
	<cfargument name="andFlag" required="false" type="boolean" default="true">
	<cfreturn galacticSearch(arguments.keywords,'jedi',arguments.andFlag)>
</cffunction>

<cffunction name="sithSearch" returnType="string">
	<cfargument name="keywords" required="true" required="false" type="string">
	<cfargument name="andFlag" required="false" type="boolean" default="true">
	<cfreturn galacticSearch(arguments.keywords,'sith',arguments.andFlag)>
</cffunction>

<cffunction name="galacticSearch" returnType="string">
	<cfargument name="keywords" required="true" required="false" type="string">
	<cfargument name="table" required="true" type="string">
	<cfargument name="andFlag" required="false" type="boolean" default="true">
	<cfscript>
		var sql = 'SELECT * FROM #arguments.table# WHERE ';
		//loop through the keywords
		for(var i = 1; i LTE ListLen(arguments.keywords, ' '); i++){
			//change the columns for each table
			if(arguments.table is 'jedi'){
				sql &= "(name = '#ListGetAt(arguments.keywords, i, ' ')#'";
				sql &= "OR planet = '#ListGetAt(arguments.keywords, i, ' ')#'";
				sql &= "OR lightsaber_colour = '#ListGetAt(arguments.keywords, i, ' ')#')";
			}else{
				sql &= "(name = '#ListGetAt(arguments.keywords, i, ' ')#'";
				sql &= "OR catch_phrase = '#ListGetAt(arguments.keywords, i, ' ')#'";
				sql &= "OR teacher = '#ListGetAt(arguments.keywords, i, ' ')#')";
			}
			if(i LT ListLen(arguments.keywords, ' ')){
				sql &= (arguments.andFlag)?' AND ':' OR ';
			}
		}
		return sql;
	</cfscript>
</cffunction>

Now if your like me, you look at this code and think “How on earth do I add another table easily and safely?”. Well you have to add a new function like “jediSearch” and then add an extra if/else into the loop in galacticSearch. Personally I’d rather not do that as it’s kind of messy and galacticSearch isn’t really the generic function I’d like it to be. Also when you edit like this you risk breaking something already working and increasing development time.

So next we move onto my solution in Pseudo-Javascript. Things of note are that we have changed the galacticSearch function to also take a columnsFunction that takes a keyword and returns the WHERE clause SQL for searching a tables columns for one keyword.

searchJedi = (keywords, andFlag = true) ->
	return galacticSearch keywords, 'jedi', andFlag, (keyword) ->
		return "(name = '#{ keyword }' OR planet = '#{ keyword }' OR lightsaber_colour = '#{ keyword }')"

searchSith = (keywords, andFlag = true) ->
	return galacticSearch keywords, 'sith', andFlag, (keyword) ->
		return "(name = '#{ keyword }' OR catch_phrase = '#{ keyword }' OR teacher = '#{ keyword }')"

galacticSearch = (keywords, andFlag = true, table, columnsFunction) ->
	sql = 'SELECT * FROM #{ table } WHERE '
	keys = keywords.split(' ')
	for i, key in keys
		sql += (if i gt 0 then (andFlag)?' AND ':' OR ' ELSE '') + columnsFunction(key)
	return sql

I think that the code is organised much tidier in the pseudo-javascript version. All the code referring to the interpretation of the keywords is in one place and all the code about searching the tables is held in another function. This in turn means that adding another table or more complexity to your keywords is not hard and you don’t risk messing up your previous code by doing it! That I think is very cool, especially if you have to work with other people/s code.

Admittedly you *could* do something similar in Object Oriented world, if you created a “Jedi” object and a “Sith” object and then coded the galacticSearch to take an object as an argument instead of a table name, but this seems like overly complicating things. Of course there is a case somewhere where passing the object is a better approach, but for most of my coding I’d rather the anonymous function approach I used in the functional programming version.

Chime in the comments if you have an opinion – I’m fairly new to functional programming so hearing from other people who know more than me is always nice!