Sagar Ganatra's Blog

I've been trying to build a CRUD application using Backbone.js and was able to retrieve a set of records into a collection using the fetch method . To perform other operations i.e. Create, Update and Delete I could always invoke Backbone.sync but I was exploring on the lines where this is performed implicitly. The fetch method sends an implicit GET request on url specified in the Collection, similarly I was looking for other methods that allow you to send POST, PUT and DELETE requests to the url. While I was building this application, I did come across a condition where Backbone was not sending a request. I was finally able to figure out as to why that happened and then it was a simple fix in my Backbone application as well as in the REST service.

From past few weeks, I've been learning Backbone.js in great detail and I think it's a great framework that helps you modularize your code easily. Last week I wrote about ' Model validation in constructor ' and then started to look at Collections in Backbone. The Model objects can be viewed as table rows and the Collection as a table. A Collection can declare the model property and indicate what kind of data it will hold. I was looking into ways in which a Collection can be populated by fetching the model data from the server. One way to do that is to ask the Model to fetch the data and then add the response to the Collection . The other way of doing this is to fetch the Collection data directly from the server i.e. instead of defining a Model you create a Collection by fetching the data from the server. Usually when you send a request to the server, the response data is essentially a collection of objects. In this case you really don't need a Model to be defined. ...

I was having a conversation with my college friend about the enhancements in XHR2 and I was showing him how one can  upload a file to the server using plain Ajax . He asked me whether I can upload a large file to the server such as a video file. I tried doing that but was bumped when the server reported with 400 error telling me that the 'POST size has exceeded maximum limit'. This got me thinking whether I can upload chunks of a large file to the server. I referred to the FileSystem API and came across the slice method that allows you to get a fragment of a file.

My Adobe Developer Connect article on 'Getting Started with RESTful Web Services in ColdFusion 10' is now live. Learn how you can get started with creating, publishing and consuming RESTful Web Services in ColdFusion. -  http://www.adobe.com/devnet/coldfusion/articles/restful-web-services.html

I’ve always liked the Virtual File System (VFS) implementation in ColdFusion, but I always griped about one thing. The files written to the VFS are available at the Server level and are not specific to an application. However, ColdFusion 10 now includes support for Application specific in-memory file system. This means that, if you write a file to the virtual file system, only those files in the same application can access it. If an attempt is made by another application to access this file, the server would happily throw an error.

I’ve been playing with the WebSocket feature introduced in ColdFusion 10 for some time now. I was trying out pushing images over a ColdFusion WebSocket channel and it worked just fine. But this time I wanted to put WebSockets to test and wanted to push large data at regular intervals. I thought maybe I can push video data over WebSockets and it turned out that there is no direct way to stream video data to many clients. I came across the function - drawImage that can be used to draw an Image or Video on a HTML5 Canvas. Once an image is drawn on the Canvas, it’s base64 encoded data can be obtained by calling the toDataURL function on the Canvas object.  This data can then be transferred over a ColdFusion WebSocket to all subscribers who can then use this  data to draw the image(video frame) on a Canvas.

The for-in loop construct in ColdFusion is generally used to loop over a structure variable. In ColdFusion 10, one can use the same for-in construct to loop over Query and List variables. Here is an example in which the for-in construct is used to loop over Query and List variables.

Yesterday Ben Nadel asked me a question on Twitter, on using filterCriteria when publishing a message on a web socket channel from server side. The method ‘wspublish’ allows you to perform a server side push to a client who has subscribed to a channel. It takes three parameters – channelName, message and filterCriteria. I always assumed that the values present in subscriberInfo and publisherInfo can be compared in Channel Listener functions (canSendMessage, beforePublish etc) before the message can be received by the client. Although this technique is available, what I found after having a discussion with a fellow developer ( Awdhesh ), is that I can specify simple conditions when subscribing or publishing.

In REST everything is treated as a resource and each resource is associated with a URI from which it can be accessed. As mentioned in my series of posts on REST ; in ColdFusion methods defined in a CFC are made RESTful by adding the attributes httpmethod and restpath. The restpath value specified in the method can then be used to access the resource. Although this would serve the given purpose, it would be a good idea to have a root resource resolve a generic URL and then have different methods that resolve other path of the URL.

I was looking into ways in which users can be authenticated before they start to receive or send messages over a WebSocket channel in ColdFusion. I found that there are two ways in which this can be done. The first approach is to call the ' authenticate'  method on the socket object. The other way is to use cflogin to authenticate the user. The authentication level can be taken a step further in various channel listener functions. By implementing these listener functions, some sort business logic can be devised wherein the logged in user with certain credentials can be allowed to subscribe or publish to a channel.

The HTML5 Web Sockets represent the next evolution of web communications. A WebSocket is a full duplex, bidirectional communication channel that operates over a single TCP socket. It has become a standard for building real time web applications. In ColdFusion 10, a messaging layer has been provided that implements the Web Socket protocol. It enables you to build applications that are based on publisher/subscriber model and applications that are based on subscriber model wherein a push from a server is possible.

A very quick post on disabling timeout for the requests. You can now set the requesttimeout to zero in cfsetting tag i.e. <cfsetting requesttimeout=0>

I was working on creating a CRUD application with REST and wanted to retrieve records with a GET request. The GET request would contain the ARTID for which the record has to be retrieved in the URL itself. To do this I had added an argument to the method implementing the GET request with ‘restargsource’ attribute set to path. The URL would be of the form: http://localhost:8500/rest/restapp/artService/getart/1 However, in another scenario I wanted to retrieve all the records from the ART table when there is no ARTID specified in the URI i.e. with the URL: http://localhost:8500/rest/restapp/artService/getart/ PathParams are always required and if they’re not specified then a ‘404 Not found’ error would be thrown. I thought of adding another method to handle this GET request with no PathParams. But, it would have made my code look clumsy and semantically not correct. However, I was able resolve this by providing a regular expression for the PathParam argument.

A quick post on the new function arraySlice added to the list of functions in ColdFusion 10. The arraySlice function is used to  select a part of the array. It takes three arguments – array, offset and length.

In ColdFusion 10, one can restrict the type of file being uploaded to the server when using CFFILE to upload the files. The new attribute accept allows the user to specify various MIME types or extensions of the file that can be accepted by the server. If the user tries to upload a file with a .txt extension but it contains xml data (application/xml MIME type) then the server would accept or throw an exception based on the value specified for the strict attribute. 'strict' is a boolean attribute added to the CFFILE tag. By default it is true and therefore wouldn't allow the user to upload a file whose contents are of different MIME type. When the strict attribute is set to false it would allow the user to upload a file irrespective of its content. However, an error would be thrown if the extension of the file doesn't match the ones specified in the accept attribute.

There are a couple of variables that have been introduced in Application.cfc which are REST specific. These are this.restsettings.cfclocation and this.restsettings.skipCFCWithError . If you have a list of directories containing REST enabled CFCs then you can specify the same in the variable this.restsettings.cfclocation. At the time of registration, the specified directories and its subdirectories will be scanned for REST enabled CFCs and then deployed. If any of these CFCs contain compilation errors then an error is thrown and the registration would fail. To tackle this another variable this.restsettings.skipCFCWithError is provided. When set to true, the CFCs with compilation errors would be skipped. Only those without any compilation errors would be deployed successfully.

Today, I wrote a post on the new lifecycle method - ‘onAbort’, which can be defined in an Applicaiton.cfc file . It is invoked when the cfabort tag is executed. David Boyer , asked me whether the onRequestEnd method is also invoked on executing the cfabort tag. In CF 9.0.1 it did invoke the onRequestEnd method. See Ben’s post: http://www.bennadel.com/blog/2221-CFAbort-And-OnRequestEnd-Behavior-In-ColdFusion-8-And-ColdFusion-9.htm Now in CF 10, this behavior has changed. The onRequestEnd method is no longer invoked when cfabort, cflocation or cfcontent tag is executed. The onAbort handler method defined in Application.cfc file would be invoked on executing these tags. Also, the onRequestEnd method would not be invoked even if the abort handler(onAbort) is not defined in Application.cfc.

I was experimenting with a new method 'onAbort' introduced in ColdFuion 10 which can be defined in an Application.cfc file. This method is invoked when cfabort is called. What if showerror attribute is also present in the cfabort tag? Would it still invoke the onAbort method and then onError? The onAbort method would be ignored and the onError method would be invoked. Even in a case wherein the onError method is not defined in Application.cfc, the onAbort method wouldn't be invoked. In this case the error message would be shown on the standard error template.

There are various complex types in ColdFusion – Array, Struct, Query. When a REST service in ColdFusion returns one of these complex types, it has to be serialized to either JSON or XML format. As explained in my previous post , the HTTP protocol can be used in content type negotiation. You can specify the desired content type either by specifying it at the end of the URL or in the Accept header of HTTP request. In this post, I’ll explain the format in which the complex types are returned from a ColdFusion REST service.

Prior to ColdFusion 10, to write or append to a file one had to specify the file content in the output attribute of CFFILE tag. In ColdFusion 10, you can specify the file content in the body of the cffile tag. In cases where the file content is specified in body as well as in the output attribute, the output attribute would be ignored.