CFWheels controllers provide some powerful mechanisms for responding to requests for content in XML, JSON, and other formats. You can build an API with ease using these functions.
If you've ever needed to create an XML or JSON API for your Wheels application, you may have needed to go down the path of creating a separate controller or separate actions for the new format. This introduces the need to duplicate model calls or even break them out into a super long list of before filters. With this, your controllers can get pretty hairy pretty fast.
Using a few CFWheels functions, you can easily respond to requests for HTML, XML, JSON, and PDF formats without adding unnecessary bloat to your controllers.
With CFWheels Provides functionality in place, you can request different formats using the following methods:
URL Variable
URL Extension
Request Header
Which formats you can request is determined by what you configure in the controller. See the section below on Responding to Different Formats in the Controller for more details.
CFWheels will accept a URL variable called format
. If you wanted to request the
XML version of an action, for example, your URL call would look something like
this:
The same would go for JSON:
Perhaps a cleaner way is to request the format as a "file" extension. Here are the XML and JSON examples, respectively:
This works similarly to the URL variable approach mentioned above in that
there will now be a key in the params
struct set to the format
requested.
With the XML example, there will be a variable at params.format
with a value
of xml
.
If you are calling the CFWheels application as a web service, you can also request
a given format via the HTTP Accept
header.
If you are consuming the service with another CFWheels application, your
<cfhttp>
call would look something like this:
In this example, we are sending an Accept
header with the value for the xml
format.
Here is a list of values that you can grab from mimeTypes() with CFWheels out of the box.
html
xml
json
csv
pdf
xls
You can use addFormat() to set more types to the appropriate MIME type for reference. For example, we could set a Microsoft Word MIME type in
app/config/settings.cfm
like so:
The fastest way to get going with creating your new API and formats is to call
provides() from within your controller's config()
method.
Take a look at this example:
By calling the provides() function in config()
, you are instructing the CFWheels controller to be ready to provide content in a number of formats.
Possible choices to add to the list are html
(which runs by default), xml
,
json
, csv
, pdf
, and xls
.
This is coupled with a call to renderwith() in the following actions. In the example above, we are setting a query result of products and passing it to renderwith(). By passing our data to this function, CFWheels gives us the ability to respond to requests for different formats, and it even gives us the option to just let CFWheels handle the generation of certain formats automatically.
You can also use the onlyProvides() call in an individual controller action to define which formats the action will respond with. This can be used to define behavior in individual actions or to override the controller's config()
.
When CFWheels handles this response, it will set the appropriate MIME type in the
Content-Type
HTTP header as well.
Responding to requests for the HTML version is the same as you're already used to with Rendering Content. renderwith() will accept the same arguments as renderView(), and you create just a view template in the views
folder like normal.
If the requested format is xml
or json
, the renderwith() function will automatically transform the data that you provide it. If you're fine with what the function produces, then you're done!
Best Practices for Providing JSON
Unfortunately there have been a lot of JSON related issues in CFML over the years. To avoid as many of these problems as possible we thought we'd outline some best practices for you to follow.
First of all, always return data as an array of structs. This is done by using the returnAs
argument (on findAll() for example), like this:
The reason for doing it this way is that it will preserve the case for the struct / JSON keys.
Secondly, make use of CFWheels ability to return the JSON values in a specified type. This is done in the renderWith()function, like this:
With that in place you can be sure that firstName
will always be treated as a string (i.e. wrap in double quotes) and booksForSale
as an integer (i.e. no decimal places) when producing the JSON output. Without this, your CFML engine might guess what the data type is, and it wouldn't always be correct unfortunately.
If you need to provide content for another type than xml
or json
, or if you
need to customize what your CFWheels application generates, you have that option.
In your controller's corresponding folder in app/views
, all you need to do is
implement a view file like so:
If you need to implement your own XML- or JSON-based output, the presence of your new custom view file will override the automatic generation that CFWheels normally performs.
Example: PDF Generation
If you need to provide a PDF version of the product catalog, the view file at
app/views/products/index.pdf.cfm
may look something like this:
HTML
Type | Example |
---|---|
html
app/views/products/index.cfm
xml
app/views/products/index.xml.cfm
json
app/views/products/index.json.cfm
csv
app/views/products/index.csv.cfm
app/views/products/index.pdf.cfm
xls
app/views/products/index.xls.cfm