C# Recursion with a Lambda

This is the first in a series about exploring the code patterns that Miguel Castro introduces in his Pluralsight course titled "Building End-to-End Multi-Client Service Oriented Applications". I am creating these blog posts as a learning exercise where I can delve deeper into the pattern and solidify my understanding of it. Hopefully this can be of some help to other programmers who are also taking Miguel's course or anyone trying to improve their C# skills.

Traditional recursion

If you're like me, when it has come to writing a recursive algorithm, you generally follow the pattern of defining a function that contains all the code that needs to be executed repeatedly and then call this from another function. It's simple and it works, but it does require that you create at least two functions. Let's take a look at an example where recursion is used to calculate the factorial for a given number:

public void TraditionalRecursion()
{
    Console.WriteLine(ComputeFactorial(5));
}

private int ComputeFactorial(int n)
{
    if (n == 0) 
    { 
        return 1; 
    }

    return (n * ComputeFactorial(n - 1));
}

The "work" is being done by the ComputeFactorial function, but as it needs to be able to call itself, it has to be created as a separate function. Like with many recursive algorithms, the first function (TraditionalRecursion) doesn't contain any logic or functionality that requires it to be separated--it just has to act as the starting point for the algorithm.

Lambda recursion

Now, wouldn't it be nice if you could do this with just a single function where you no longer need a second function just to start the algorithm. Imagine being able to define the recursive algorithm and start it all within the same function. Well, it turns out that this is quite easily achievable through the use of a lambda expression:

public void LambdaRecursion()
{
    Func<int, int> computeFactorial = (n) =>
    {
        if (n == 0) 
        { 
            return 1; 
        }

        return n * ComputeFactorial(n - 1);
    };

    Console.WriteLine(computeFactorial(5));
}

The inline delegate, a Func in this example, contains exactly the same behavior as the ComputeFactorial function; the only difference is that it has been declared as a variable. An easy way to look at this, is to image that ComputeFactorial has been wrapped up and is now contained within the computeFactorial variable (declaring functions as variables should be very familiar concept to a JavaScript programmer). Once declared, all you have to do it call this variable to start the recursive algorithm--it really is as simple as that!

SPA Silos

I was recently listening to a fascinating .NET Rocks podcast which featured Miguel Castro discussing MVVM on the Web. Miguel talked about his experiences with Knockout.js and AngularJS as client side MVVM frameworks. What I really enjoyed about this podcast was the insight he brought to the table of developing commercial SPA's (Single Page Applications) but using a more hybrid approach. What am I saying here? I think Miguel used the phrase “pages with SPA pockets” but said Brian Noyes coined a much more accurate description—SPA Silos.

SPA Silos are where a single web application is actually made up of many SPA’s. When we envisage creating a SPA, we normally have a vision of a single HTML base page that will initially load all of your SPA code. From there the browser will not actually request any new pages from the server but only swap out views and make web API calls in the background as you navigate around the app. The SPA Silo approach is to break that single SPA into many mini SPA’s each responsible for its own area of functionality. Navigation within the mini SPA is handled by routing in the SPA framework. When moving to different areas of the application, this is handled by requesting a new page from the server which bootstraps all the SPA code for the mini SPA that will provide the functionality for the area of the application you are now navigating to.

Miguel gave a nice example which helped illustrate this practice very well:
Let’s say you are building an e-commerce management web application. The application would have areas such as Products, Customers, Orders, Admin etc. Instead of having a single SPA which contained the functionality for all of these areas, you would actually have 4 mini SPA’s which are each loaded when navigating to the required area instead of upfront when first loading the application.

What are the benefits from using this hybrid SPA Silos approach I hear you asking? There is one very big benefit which immediately springs to mind--Separation of Concerns. I cannot stress the importance of this principle enough. If this hybrid approach was not used you would have one very big SPA application with potentially a very complex and large routing table as well as a very large code base. By breaking the application out into many smaller applications you now only need a routing table for the area your application is concerned with (products or customers for example). Another benefit is that the code base for each area of the e-commerce management application is modularised due to it being implemented in a self-contained SPA. This will help make finding the required code easier assisting with maintaining and enhancing the web application in the long run. SPA applications force the browser to work in a way it was never originally designed to. Browsers work best when they can navigate from page to page and forget everything that happen on the previous page. They like to "wipe the slate clean". SPA’s force the browser to stay on a single page but update the current page's content dynamically as the user navigates around the application. This behaviour could lead to memory leaks as a browser could go for hours, days or even weeks without the page actually being refreshed. This hybrid model helps encourage page refreshing as each time the user moves from one area of the application to another, the application will make a page request and the browser will be breathing a sigh of relief. Of course, if the user were to spend all their time in a single area of the application the original problem will still be present. However, with the hybrid approach the functional surface area which a user can operate in without triggering a page refresh is greatly limited, increasing the likelihood of a page refresh occurring on a more regular basis.

On the downside there is the added complexity of handling a combination of client-side and server-side routing within the web application but I feel this is outweighed by the benefits of this approach.

Miguel will be presenting a session on this approach at NDC London in December so I will be watching this session as soon as it’s posted on their Vimo channel. If you cannot wait until then, Miguel's Building End-to-End Multi-Client Service Oriented Applications - Angular Edition course on Pluralsight also provides an insight into this hybrid approach.

Quoting Miguel, "It’s the best of both worlds".

EDIT:
You can find Miguel's talk at NDC London here: AngularJS for ASP.NET MVC Developers by Miguel A Castro.

Think Twice Before Changing your APIs

How often do you make changes to a service that actually alter the API itself? I'm sure if I asked this question to an experienced developer the answer would follow something along the lines of "You would NEVER want to do that! If you change the API, you risk breaking any applications that are consuming that service." As this danger is fairly well known, how do you guard against it?

Imagine this scenario: there is a set of web services that are being consumed by multiple web applications. The API for one of these services has been changed so that a service method that was taking a string, is now taking an integer. Unfortunately, this little change caused the contract surrounding the service to also change, which meant that any applications consuming it would also need to be updated. It wasn't until another application started to throw exceptions that it became clear that one had been missed.

If this was a new area of development, a contributing factor to this oversight could have been that the developer making the change might have not known that the contract they were changing was already being consumed by multiple applications. The developer might have assumed that it was OK to change the contract because the code was "very young" and it couldn't have been integrated with other applications in such a short time frame. If anything this highlights why you can’t rely on a developer to catch this as they can't be expected to know of where each service method is being used.

The fix is simple, but could this have been avoided in the first place? A simple solution would be to never alter the API of a service, ever. The problem with this is that it is still comes down to the developer to ensure that this is being followed. Remember that in my example, the service method had been only been created very recently so it's conceivable that another developer would also assume that they were dealing with the only occurrence where the service method was being consumed. Documentation and improved communications between developers would help to identify an issue, but it would still be up to the developer to notice it.

An ideal solution would be automated so that a developer would not need to be aware of how an API is being consumed. If this could be created as a set of tests that are run as part of a build process, any issues would be identified well before deployment to production. To achieve this, you would need the ability to stage the service in a test environment where you could fire off requests to verify that the API has not changed. Another possibility would be to compared the current WSDL file with a previous version to check for changes.

If you find yourself considering altering an API, be sure to take a moment to ask yourself why. Can you extend the current contract to ensure that the API will not be broken instead of changing it? In most cases, this should be the preferred course of action and making changes to the contract should only happen when there really is no other choice.

Bootstrap 3's Grid System

I have been playing with Bootstrap 3's grid system and have found it to be a very clever general purpose grid system for assisting developers with the layout of their sites. It also helps lead you to developing a responsive design which adapts to the size of the screen size it is being displayed on. To help cement these concept in, I quickly created a demo site which allowed me to view bootstraps responsive design features in action.

You can find that site here. 
Adjust the width of the page and see how the grids layout automatically adjusts with you. These adjustments go beyond shrinking the width of a column but allow you to specify different column sizes for specific view ports. This opens up lots of options for re-arranging your site to make it just as usable on a phone, tablet or laptop.

Bootstrap goes beyond just allowing you to apply different widths to a column within a grid though. It also provides you with the ability to show and hide columns based on the width of a page. This provides you with even more functionality to empower your sites responsive design.

How does Bootstrap do this? It's all through the use of CSS media query's. Media query's allow specific CSS to be applied when certain condition are met. In the case of the Bootstrap grid system, these conditions are based on the width of your page. Take a look at the Bootstrap 3's docs to get a better understanding of how this works and the grid system in general.

With CSS frameworks like Bootstrap, HTML5 Boilerplate and Pure, its getting harder and harder to NOT create a responsive site.

Using dynamic and DynamicObject in C#

Up until I came across Simple.Data, I had only used the dynamic type when unit testing controllers that returned JsonResult objects. After playing with Simple.Data and taking a look at the source code, it became clear that there was a lot more to the dynamic type than I had realized; it hadn’t occurred to me that you could use the member’s name essentially as an additional argument (thanks Jon for making me see this!). To better understand all of this, I decided to create my own limited implementation that would allow me to execute stored procedures in the same fashion. VerySimpleData is heavily based on Simple.Data and I am not trying to take any credit for the creativity of this approach. I have tried to keep my implementation as lean as possible to highlight the use and function of the dynamic type.

VerySimpleData

First of all, you can find the repository for VerySimpleData here.

I’m sure you’re familiar with how the compiler will bark at you if you make a typo and end up calling a method or setting a property that doesn’t exist. That’s static typing at work making sure that everything your code is talking about actually does exist. The dynamic type allows you to sidestep this and by-pass what would normally be resolved at compile-time and instead have it resolved dynamically at run-time. This means that you now can call methods or set property that do not exist, as long as you’re using a dynamic type. Let's start with an example of how to use VerySimpleData to highlight this.

1 2	var database = Database.WithNamedConnectionString("connectionString"); var results = database.MyStoredProcedure(Param: "something", AnotherParam: "something-else");

In line one, the connection string is supplied and a dynamic object is returned which will act as the database context. In line two, I am calling a stored procedure called "MyStoredProcedure" and passing it two parameters called "Param" and "AnotherParam"; if I wanted to execute a stored procedure with a different name and/or parameters, I would only need to change the method's name and the names of the parameters that are being supplied:

var results = database.AnotherStoredProcedure(DifferentParam: "something-different");

Looking Under the Hood:

The entry point to VerySimpleData is through one of the static methods on the Database class:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

public static class Database { public static dynamic WithNamedConnectionString(string name) { var connectionStringSettings = ConfigurationManager.ConnectionStrings[name]; if (connectionStringSettings == null) { throw new ArgumentException("No connection string found for: " + name); } return WithConnectionString(connectionStringSettings.ConnectionString); } public static dynamic WithConnectionString(string connectionString) { IDatabase database = new SqlServerDatabase(connectionString); var dynamicContext = new DatabaseContext(database); return dynamicContext; } }

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public class DatabaseContext : DynamicObject { private readonly IDatabase Database; public DatabaseContext(IDatabase database) { Database = database; } public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { if (binder.CallInfo.ArgumentCount != args.Length) { result = false; return false; } var procedureName = binder.Name; var parameters = binder.CallInfo.ArgumentNames.Zip(args, (s, i) => new { s, i }) .ToDictionary(item => item.s, item => item.i); result = Database.ExecuteStoredProcedure(procedureName, parameters); return true; } }

An instance of DatabaseContext is returned from the Database static class as a dynamic type when either WithNamedConnectionString() or WithConnectionString() is called. The key to this class is that it inherits from DynamicObject. DynamicObject provides the ability to interact with any of the members that are executed/set on the dynamic type by overriding the base implementation:

TryInvokeMember is invoked whenever a method is called on the dynamic object. By providing your own override of this, you can control what will happen. The example in DatabaseContext.cs is very simple. First there is a check that the argument count matches the number of arguments that were supplied. From a quick inspection, the InvokeMemberBinder appears to contains meta data/semantics about the invoked member (e.g. the names of the arguments, the name of the member being invoked) whereas the values themselves are contained on the args array. It is important to note here that the “out” result parameter holds the object that will be returned when this member is invoked; the returned Boolean for TryInvokeMember indicates if the operation was successful or not. Returning false causes a Microsoft.CSharp.RuntimeBinder.RuntimeBinderException to be thrown. This pattern is the same for all the Try[…] overrides exposed from inheriting from DynamicObject.

My implementation assumes that the name of the invoked member will match the stored procedure’s name (line 19) and that the names of the arguments will match the procedure’s parameters (lines 20-21). Calling the ExecuteStoredProcudure method (line 23) fires off the ADO.NET code that talks to the database and it should be no surprise that this returns a dynamic object as the result could be a single value, a single record, a set of records or nothing at all.

If there’s only one row and multiple columns, this will be returned as a VerySimpleDataRecord:

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public class VerySimpleDataRecord : DynamicObject { private readonly Dictionary<string, object> _data; public VerySimpleDataRecord() :this(new Dictionary<string, object>()) { } public VerySimpleDataRecord(Dictionary<string, object> data) { _data = data; } public override bool TryGetMember(GetMemberBinder binder, out object result) { if (_data.ContainsKey(binder.Name)) { result = _data[binder.Name]; return true; } return base.TryGetMember(binder, out result); } public override bool TrySetMember(SetMemberBinder binder, object value) { _data[binder.Name] = value; return true; } public int ColumnCount { get { return _data.Count; } } }

This is constructed using a dictionary collection where the key-value pairs comprise of the column name and the data that was held in that column. The TryGetMember override is invoked when performing a property get operation on the dynamic object; if there is a key in the dictionary collection that matches the property’s name, it is returned.

The final scenario is where there are multiple rows with one or more columns. In this case, a collection of data will be returned that is packaged in a way that make it enumerable:

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public class VerySimpleDataRecordSet : DynamicObject, IEnumerable { private readonly IList<VerySimpleDataRecord> _data; public VerySimpleDataRecordSet() : this(new List<VerySimpleDataRecord>()) { } public VerySimpleDataRecordSet(IList<VerySimpleDataRecord> data) { _data = data; } public override bool TryGetIndex(GetIndexBinder binder, object[] indexes, out object result) { if (indexes.Length == 1 && indexes[0].GetType() == typeof(int)) { result = _data[(int)indexes[0]]; return true; } result = false; return false; } public int Count { get { return _data.Count; } } public IEnumerator GetEnumerator() { return _data.GetEnumerator(); } }

A VerySimpleDataRecordSet is initialized by supplying a collection of VerySimpleDataRecords. Like the dictionary collection in the VerySimpleDataRecord, this is stored internally. VerySimpleDataRecordSet also inherits from DynamicObject that provides the TryGetIndex override. When this is invoked, the supplied index value is first validated and if it passes, the appropriate VerySimpleDataRecord is retrieved from the internal collection and returned. The ability to enumerate the VerySimpleDataRecordSet is achieved by implementing IEnumerable: the GetEnumerator method exposes the internal collection’s IEnumerator.

I have only touched a few of the method overrides that are available through DynamicObject mainly to do with getting and returning data. There are other operations to do with setting values and performing conversions that would be worth exploring.

SQL - Beyond the standard ORDER BY ASC / DESC

Recently at work a request came in from a user to update an existing report so it applied a specific order to the reported data. Previously the report ordered items alphabetically by Class and then Model, however, this was no longer suitable and a non-alphabetical ordering was required. 
Initially when I read this requirement I thought “Oh heck, how am I going to do this as it’s no longer in alphabetical order?”. As is often the case, the solution was simpler than expected.
I have created a simplified representation of the data in use to illustrate the technique I used to accomplish the custom sort order below.

User Requirement:
Order products in the following Class order
R-Class
ZA-Class
T-Class
G-Class
J-Class

As discussed earlier, this is not in alphabetical order so the following SQL statement will not produce the required result:

SELECT Model, Class
FROM Products
ORDER BY Class, Model

As we need to apply a specific order, we can accomplish this by introducing an additional numeric field into the result set which is solely used for ordering the results. This additional field can be produced by using a CASE WHEN statement to determine the correct numeric value to ensure the correct ordering is applied.

SELECT Model
 , Class
 , CASE
  WHEN Class = 'R-Class' THEN 1
  WHEN Class = 'ZA-Class' THEN 2
  WHEN Class = 'T-Class' THEN 3
  WHEN Class = 'G-Class' THEN 4 
  WHEN Class = 'J-Class' THEN 5      
 END AS ProductClassOrdering
FROM Products
ORDER BY ProductClassOrdering, Model

The ProductClassOrdering field will contain a numeric value which can be used as part of the ORDER BY clause to ensure the users custom ordering is applied.

Boom! This technique creates the desired result but it also introduces the use of an interesting technique: creating a field dynamically as part of your result set. It can be very easy to believe a SELECT statement can only select static data from a table (I will admit I was guilty of this belief when I first learnt SQL) but this is not true. If you start viewing each select value as a piece of data which can be generated by other means within the SQL languages constraints, you will find a whole new range of querying options available to you (sub-selects, logic to determine a value, additional filtering to name a few). 

However, a word of warning is needed. With these additional SQL powers comes great responsibility which can be summarized in a single word: performance. Keep one eye on the performance of your query when introducing additional SQL statements into the SELECT portion of your query as you can inadvertently introduce performance bottle necks into your query. 

Have a play and start flexing those SQL muscles a little more.

Development Environment Revolution 2.0

Looking back, my home development setup has gone through a couple of revolutions over the years. These revolutions have resulted in some drastic changes in my home development activities.

It all started with the desktop PC - Big, bulky and fixed to one location. Developing at home often felt like a chore as you were glued to a desk usually placed in a room out of the way.

Revolution 1 - The laptop.
It was brilliant not having to be sat at a desk when developing / studying in my free time. Being able to be sat in the front room instead of stuck at a desk was a game changer for me. It made it feel a lot less like work. However, originally laptops which are desktop replacements were bricks and difficult to pick up and walk around with. You also needed some sort of tray to help keep them well ventilated underneath plus forget taking it anywhere with you unless you are prepared for a mini workout. Things are much better these days with the advent of the ultra book. I would argue that the form factor of a laptop (screen physically attached to a keyboard) is not ideal for all use cases as there are times where you do not really need a keyboard - reading an ebook or browsing the web for instance. A good move forwards but still not quite perfect.

Revolution 2 - The Tablet.
You can truly develop anywhere. In bed, in the back garden, in the car, on the train or bus. I choose to go with an 11 inch Atom powered tab. A lot of people who I have told about this have said, "Hey, you must have the i5!?" Nope - Just the Atom processor option and it's more than capable. "Can you work on such a small screen?" Yep! I can have Visual Studio open on half the screen (drop the text size 8pt and you are rocking) and a Pluralsight video / internet browser running on the other half with a workable amount of development real-estate on offer. 
I find it helps encourage me to dive in and do some coding / studying whenever I have a few moments spare as it starts up so fast compared to my previous laptops (5 second to loading up Windows - 10 seconds if you want to be coding in Visual Studio).
I would recommend getting a detachable keyboard for your tab as it will make a huge difference to your development experience - If it has an additional battery built in, all the better! It is also nice having the option of disconnecting the keyboard if you only want to use the tab for reading / browsing.
I will admit, for heavy lifting development work you may need something a bit more beefier but with cloud storage, compute and persistence options becoming much more cheaper to access, there are plenty of other options available. (Free on Azure with an MSDN license)
I dare you, take the plunge and get yourself a latest generation Windows tab as your home development environment and tell me it has not helped revolutionized the way you code / study at home.