Intro to ClojureScript - Part 2 - Getting the Stats

In this post we will flesh out the backend of the app we started in Intro to ClojureScript - Getting Started. We are going to create a web service to lookup player stats by last name. Once we have the lookup service in place we will update search.cljs to fetch the results of our query using the Google closure library’s goog.net.XhrIo. When the data is returned we will display it to the user using the hiccups library.

Since ClojureScript is a bit of a mouthful I will use the abbreviation cljs for the remainder of this post. Remember I am learning cljs as I create these posts so any and all guidance is appreciated.

The Goal

By the end of this post we will have a web based app that will lookup player stats by last name, displaying the results of our search.

The Setup

If you don’t already have cljs setup on your machine read my Getting Started post. It will walk you through the necessary steps to set up your cljs environment. I am also assuming you have the code from the first post. If not you can grab it from my cljs-intro github repo.

Grabbing the DB

We will be using a SQLite version of my hockey stats database. You can download it from my hockeydb github project. Once you have the database, create a db directory in the project’s home directory and copy the downloaded database into it.

Project.clj Changes

Since we will be interacting with a database, manipulating the page’s DOM, and creating a web ‘service’ we need to add a the following dependencies to our project:

[org.clojure/java.jdbc “0.2.3”]
[sqlitejdbc “0.5.6”]                  
[domina “1.0.0”]
[noir “1.3.0-beta0”]
[hiccups “0.1.1”]

The first two libraries are for our database interaction. The domina library allows us to manipulate the DOM from our cljs code. We will use noir to create our lookup web service. The hiccups library will be used to add and remove HTML from the web page.

The last setup step is to update the resources/public/index.html file. Most of the changes in it are for twitter bootstrap support. Adding bootstrap will make the search results a little easer to read.

The only change needed for the application is the addition of results div. As you might of guessed this is where the div that will contain the search results.

Creating the DB Access Code

All of our database related code will live in src/clj/cljs_intro/db.clj file. The code does a few simple queries to gather the player related information. I’m not going to go through this code in detail since it is ‘normal’ Clojure and not cljs. If you'd like to see the code here's the link to at github: db.clj.

In the db.clj file I’ve made the executive decision to return the stats for the first matching player. Why? I don’t wan’t to spend a bunch of time on non-cljs code so I made it simple on myself. What does that mean? It means if you search for Gretzky you’ll get Brett Gretzky instead of Wayne. I bet you didn't know there was a Brett Gretzky did ya.

Creating ‘Web Server’

Now that we have the database its time to create our simple web server. Noir provides functions that allow us to respond to HTTP requests, mapping routes to code and return JSON data. Our server will listen on the port 8888 for following two URLs:

http://localhost:8888/index.html
http://localhost:8888/player/:lastname.

The last URL has a parameter (:lastname) which will be the player’s last name entered by the user. Any other request will throw a Noir error.

Now that our server is complete we need to update the project.clj file so we can start it by running `lein run`. Add the following to the project.clj file:

:main cljs-intro.core

Lets test the server out. At the command prompt enter:

lein run

When the server starts up open your favorite browser and go to http://localhost:8888/player/ricci . If everything goes well you should see about a page full of JSON data.

Retrieving and Displaying the Data

If you go to http://localhost:8888/index.html and enter ricci in the text box and click the ‘Get Stats!’ button you’ll see an alert box with ricci in it. That was fine for part 1 but now we are ready to get the stats. In order to do that we need to update the ‘Get Stats!’ click event handler. Instead of a js/alert call we will call our player-lookup function.

The Updated Click Event Handler

The player-lookup function wraps a call to the Google Closure library’s goog.net.XhrIo.send method.

The goog.net.XhrIo.send function has two parameters, the URL to call and a callback function to process the returned data. We create the URL parameter by concatenating the base URL (/player) with the user’s input, in our example its ricci. When the call returns the data is passed to the display-results function so we can, well display the results.

display-results

The display-results converts the returned JSON data into a Clojure data structure and manages the UI updates.

The call to js->clj coverts the JSON to a Clojure data structure. A key thing to note here are the parameters :keywordize-keys true. Before I used those two parameters I was having a hell of a time getting to the data. After using the parameters I could easily access the data using keywords. I’m assuming that most of the time you use js->clj you’ll want to add :keywordize-keys true.

The next line uses the domina.xpath/xpath function to get a reference to the results div DOM object. We will use the reference to display the search results.

Before displaying the results of the current query we remove any previous query results by using the domina function called destroy-children!. The parameter for the destroy-children! function is a reference to a DOM object with the children to be removed. Now that the display area is empty we can display the results of the new search. On the last line a call is made to cljs-intro.views/show-stats which is where the HTML generation process starts. The results of that call are appended to the results div by calling domina’s append! function.

The HTML

Creating the HTML is done using the hiccups library which is a port of the Clojure hiccup library. Since I've used hiccup and noir for non-cljs web-based apps using hiccups made the HTML generation easy. The only difference I saw between hiccups and hiccup was that I had to use defhtml when creating a function that generated HTML.

If you wish to view the code that generates the email you can see the views.cljs. Now, when we run the search for Ricci we see the following page displayed:



Summary

The search app makes a remote call using the Google Closure library. When the data returned we were able to convert the JSON to a Clojure data structure. Once the conversion was complete we used the domina library to remove and add HTML with help from the hiccups library. Our application actually returns the stats for the player (as long as you only want the first person with the last name in question).

Whats Next?

In Intro to ClojureScript - Part 3 - Using Shoreleave - we will use the Shoreleave libraries to decouple the front end from the back end by using event based messaging. We will also change the way we handle the remote calls to use the shoreleave-remote library.

Resources

twitterbuzz and this stack overflow post implementing an ajax call in clojurescript helped me with the remote call.

ClojureScriptOne.com - used for DOM manipulation guidance.

Hockey Databank Database -- I created the database using data that originates from a Yahoo! group called hockey databank. After each season the group produces updated CSV files with the stats of the previous NHL season in addition to previous years data.

ClojureScript Experience Report - Resources Bits of information about Jason’s ClojureScript based application and his experience with ClojureScript.

ClojureScript: Up and Running - An early release book that discusses ClojureScript. I’ve read the released chapters and found it to be a good resource. Chapters 2 and 3 go over ClojureScript’s compilation, project structure, and other informative tidbits for both ClojureScript and Clojure. I’ve recommended the book to a colleague who is learning Clojure because of the way the authors describe data structures, immutability and sequences.

cljs-intro - My github repo that stores the code for this blog series. The code for Part 1 can be found on the branch Part 1. This post’s code is on the Part 2 branch.

Intro to ClojureScript - Getting Started

I’ve been curious about ClojureScript for awhile now but for whatever reason I hadn’t taken the plunge. A few weeks back I attended a at talk at a TriClojure meetup titled ‘A ClojureScript Experience Report’. Jason broke down his experience creating an app using ClojureScript ins such a way that it motivated me to start learning ClojureScript.

This is the first in a series of posts that I will write that chronicles my journey down the ClojureScript path. I will be building out a basic app to lookup hockey stats by the last name of a player. Keep in mind I’m learning ClojureScript as I write these posts. If you have experience with ClojureScript and you see me making errors or not doing things in a idiomatic way please feel free to point out the errors of my ways.

Since ClojureScript is a bit of a mouthful I will use the abbreviation cljs for the remainder of this post.

The Goal

By the end of this post you will have an environment that is ready to create cljs apps. You will also have the beginnings of our hockey stats lookup app.

The Setup

Before you can start writing you app you’ll need to get your environment setup. The first step is to get Leiningen installed. Follow the directions on the page and you’ll be ready to create your first project.

Creating a cljs project is done the same way you create a Clojure project:

lein new cljs-intro

This will create Clojure project with the following layout:

README
project.clj
src
    cljs_intro
         core.clj
test
   cljs_intro
         test
               core.clj

In order to keep our Clojure and cljs code seperate we need to change the directory layout of our project a little bit. We need to add two directories, move the existing Clojure code and create the directory for housing our HTML and cljs compiler output. If you are in the project’s home directory run the following commands:

1. mkdir src/clj src/cljs
2. mv src/cljs_intro src/clj
3. mkdir -p resources/public

Now that we’ve created the directories and moved the code we need to update the project.clj file to reflect these changes and add cljs specific settings.

The project.clj file generated by the lein command looks like this:

First we need to add the plugin lein-cljsbuild to the project. lein-cljsbuild is the plugin that makes it possible to compile cljs apps. Adding lein-cljsbuild to our is as simple as adding the :plugin line to the project file. Here’s what the updated project.clj file looks like after adding the line.

Since we moved the source code location we need to update the project.clj file to reflect those changes. By adding the following line the file we inform lein where the Clojure code lives.

:source-path "src/clj"

Now its time to set up the cljs related settings. Here’s what we need to add to the project file:

Here we are we are telling the cljs compiler to output the results of the compilation into the file resources/public/hockey.js. Since we have an optimization setting of :whitespace all compiled javascript will be placed into a single file. There are four levels of optimization levels available: :none, :whitespace, :simple and :advanced. We will stick with the :whitespace option. The :whitespace setting removes comments and any unnecessary whitespace in the source code but leaves the remaining code alone. The book ClojureScript: Up and Running has a nice discussion about optimization. The :pretty-print option gives us output that is a little easier to read. Here’s what the updated project.clj file looks like:

To ensure we have everything correct in the project.clj file go ahead and start the Clojure repl by running this command:

lein repl

If everything is OK you should see something like this:

REPL started; server listening on localhost port 42236
user=>

Time to Write Code

Now that we have our project setup for cljs its time to start writing some code. For this post we will create the search form which will have a text field and a button. The ‘back end’ of the form will be written using cljs and will be responsible for responding to the search button click. When the button is clicked the cljs code will grab the value of the text field and displaying it in an alert box.

resources/public/index.html

Before we write the cljs code lets create the HTML page. Its a simple form that has a text box and a button. Here’s what the HTML looks like:

The only real line of note here is the script tag. It references the file that we will generate when we compile our cljs code.

src/cljs/search.cljs

The src/cljs/search.cljs file is where we will put the code to handle the user’s input. Once you have created the file open it in your favorite editor and add the following lines:

The above code sets the namespace for the code and brings in the domina and clojure.browser.event libraries. We need the domina library so we can interact with the DOM. The clojure.browser.event library is used to add the event handler for the button’s click event.

Before we write the search button's click event handler lets get a reference to the search button itself.

(def search-button (d/by-id "search-btn"))

We get a reference to the button by making use of domina's by-id function and store the reference to the DOM object in search-button. Now its time to create the event handler.

The clojure.browser.event/listen function creates the relationship between the search button’s click event and our handler function. We create a function to popup an alert box containing the contents of the text field.

Compile Time

To compile the cljs code we have two options: lein cljsbuild once or lein cljsbuild auto. The once option compiles our code like a ‘normal’ compiler. It runs, compiles the source and puts the output to the file that we indicated in the :output-to setting. If we compile with auto every time a cljs file is saved the compiler will run. For now we’ll stick with the once option. To compile our code go to anywhere in the project’s directory structure and enter:

lein cljsbuild once

Now open up the the HTML file we created in the browser and you should see a beautifully designed form that looks something like this:

Enter the string ‘ClojureScript!’ in the text field and click the ‘Get Stats!’ button. You should see something like this:

We now have the beginnings of our stats lookup app. The user interaction is in place but we don’t really have a lot of the ‘under the covers’ code in place. In my next post we will add code to the hockey database and run an actual query!

Summary

In this post we went over how to get your environment set up for ClojureScript. We also went over the necessary changes to the project directory structure and project.clj file. We also created a simple cljs file to handle the user’s input in our search form.

Whats Next?

In Intro to ClojureScript - Part 2 - Getting the Stats we will create the necessary back end to retrieve data from the database and display it on the page.

In Intro to ClojureScript - Part 3 - Incorporating ClojureScriptOne - We will add support for messaging. We will add a new feature with messaging.

Resources

ClojureScriptOne.com - A sample project to help people get familiar with ClojureScript.

ClojureScript Experience Report - Resources - Bits of information about Jason’s ClojureScript based application and ClojureScript.

ClojureScript: Up and Running - An early release book that discusses ClojureScript. I’ve read the released chapters and found it to be a good resource. Chapters 2 and 3 go over ClojureScript’s compilation, project structure, and other informative tidbits for both ClojureScript and Clojure. I’ve recommended the book to a colleague who is learning Clojure because of the way the authors describe data structures, immutability and sequences.

cljs-intro - My github repo that stores the code for this blog series.

Creating a TFS Work Item from ClojureCLR

At my day job we use Team Foundation Server 2008 (TFS) for our automated builds, iteration management, and source control. TFS may not be the most ideal way to manage these processes but in our MS environment it has helped us communicate with our non-technical team members and customers.  So we’ve been looking into ways to add bugs automatically when automated tests fail (see Creating A TFS WorkItem From IronRuby) or errors are reported from our applications via a message queue.

This morning I had a little time to do some ‘research’ on how to programmatically create a new bug work item.  My goal was to write code that would create a new work item bug with an image attached to it.  Before I get into the code let me take a second to introduce you to a TFS Bug Work Item.

A TFS Bug Work Item

In TFS Work Items are a way to track work that needs to be done. There are a total of five different type of Work Items available but we typically only use three: Task, Scenario, and Bug. Each Work Item type UI has different fields. Here is what a Bug Work Item looks like in our environment.

In this example we will create a new bug and enter text into the highlighted fields plus attach an image file. In order to create the bug I need to do a little setup.

The Setup

There are three assemblies needed to create a TFS Bug Work Item. The are: Microsoft.TeamFoundation.dll, Microsoft.TeamFoundation.Client.dll, and Microsoft.TeamFoundation.WorkItemTracking.Client. All three of these DLLs can be found in the C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies directory. I copied the three Dlls into the project’s libs directory.

The Code

The first step is to load the TFS assemblies from libs directory using the assembly-load-from function. I follow that call up with the import function pulling in the specific classes I need.  Once the assemblies and classes have been loaded I can start working on creating a bug work item. First, I created the -main function. The first few lines of –main are responsible for creating the necessary objects for WorkItem creation.

The first line gets the server object by making a call to the static method TeamFoundationServerFactory.GetServer passing in the name of the server I am working with.  The returned server object is used to create a WorkItemStore object.  A WorkItemStore encapsulates the data store that contains all work items on a particular server.  The next line gets the TFS project that I want to work with by using the filter function.  The last setup line uses the project object to retrieve the WorkItemType object that represents a bug.  Now I 'm are ready to create a new bug WorkItem.

Creating the Bug WorkItem

Since I will be creating bugs that have attachments and bugs that do not I created a function that creates and returns a WorkItem object. As I stated previously, the work items created this way will have the bare minimum values: title, area, iteration and description. The code is straight forward, just create the WorkItem object by passing in the WorkItemType object. Next I set the properties of for the four parameters. When everything has been set I return the WorkItem object.

Adding the Attachment

Now that I have my WorkItem object its time to add my image file as an attachment. I wrote another small and simple function to create the Attachment object. It takes three parameters, the WorkItem, the path to the file to attach and a description of the file.  First I use the path and desc parameters to create the Attachment object.  After the Attachment is created I can added it to the WorkItem object’s Attachments collection by calling the Add method passing the Attachment object as its only parameter. 

At this point I have a WorkItem object with an Attachment in memory.  At this moment the WorkItem is not visible through the TFS toolset.  I still have one last line of code to write to ensure that the WorkItem is saved. Surprisingly enough all I need to do is call the WorkItem’s save method.

(.Save work-item)

Now, If I look at the Pending Bugs report in TFS I will see my newly created bug in the list.

Summary

This post is another illustration of how easy it is to use .NET Assemblies from ClojureCLR.  In this case I walked you through the simple process of creating a Bug WorkItem in TFS.  Having the ability to programmatically create and report bugs will help us close the feedback loop in our applications. 

In The Future

In my ‘free time’ I will be checking into TFS’s build and source control APIs to see what we may be able to do improve our processes.  If and when I find anything of interest I will be sure to do a post or two about my findings.

Resources

TFS API: http://msdn.microsoft.com/en-us/library/bb130146(v=vs.90).aspx

My Source (this blog’s code is the 5-create_tfs_work_item):https://github.com/rippinrobr/clojure-clr-intro/zipball/master