C# CSV Library and HTTP Handlers

A colleague and I was recently looking at some old ASP.NET WebForms code which generated a potentially large CSV string and returned it in a response to a HTTP request. The original code was placed in a standard ASP.NET WebForms page in the OnLoad event handler. As the code was working with the HttpResponse object and writing the CSV directly to the HTTP output stream, we determined that this code was better placed in a HTTP Handler. The primary advantage of using a HTTP handler to generate the file is that we can bypass the unnecessary ASP.NET WebForms page life cycle.

The existing code was using a StringBuilder to generate the CSV string in the page OnLoad event handler. As you may imagine, this looked messy and was a pain to maintain. To abstract the CSV string creation logic, my colleague introduced me to a useful CSV library called LINQ to CSV. The project page link for this library is here and the library is available as a NuGet package.

The LINQ to CSV library enabled us to decorate some properties in a model class with attributes that specify how to output the property in CSV form. The example below (from the library project page) shows how to apply the attributes:

public class Product
{
    [CsvColumn(Name = "ProductName", FieldIndex = 1)]
    public string Name { get; set; }
    [CsvColumn(FieldIndex = 2, OutputFormat = "dd MMM HH:mm:ss")]
    public DateTime LaunchDate { get; set; }
    [CsvColumn(FieldIndex = 3, CanBeNull = false, OutputFormat = "C")]
    public decimal Price { get; set; }
    [CsvColumn(FieldIndex = 4)]
    public string Country { get; set; }
    [CsvColumn(FieldIndex = 5)]
    public string Description { get; set; }
}

Once your model class is decorated, you can then use other classes of the library to generate a CSV representation of a collection containing your model instances. This representation can be output to disk as demonstrated in the code example below:

IList<Product> products = new List<Product>();
products.Add(
    new Product
    {
        Name = "Samung Galaxy S6",
        LaunchDate = DateTime.Today,
        Price = 500,
        Country = "United Kingdom",
        Description = "This is a Samsung phone product"
    }
);

products.Add(
    new Product
    {
        Name = "Apple iPhone 5",
        LaunchDate = DateTime.Today,
        Price = 600,
        Country = "United States",
        Description = "This is an Apple phone product"
    }
);

CsvFileDescription inputFileDescription = new CsvFileDescription();
inputFileDescription.SeparatorChar = ',';
inputFileDescription.FirstLineHasColumnNames = true;

CsvContext csvContext = new CsvContext();
csvContext.Write(products, @"C:\Products.csv");

Usefully, the CsvContext class of the library also supports an overload to the Write method which accepts a TextWriter stream. Passing a TextWriter stream to this overload results in the library outputing the CSV representation to your stream rather than a file on disk. In our case, we used a StreamWriter that wrote to a MemoryStream. Once the CSV file content was in the MemoryStream instance, we sent the stream contents in the HTTP response from the HTTP handler. The full HTTP handler code is below (using the example product data).

public class ProductsExportHandler : IHttpHandler
{
    public bool IsReusable { get { return true; } }

    public void ProcessRequest(HttpContext context)
    {
        context.Response.AddHeader(
            "content-disposition", 
            "attachment;filename=BulkExport.csv"
        );
        context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
        context.Response.ContentType = "application/vnd.text";

        IList<Product> products = new List<Product>();
        // Add products...
            
        var inputFileDescription = new CsvFileDescription();
        inputFileDescription.SeparatorChar = ',';
        inputFileDescription.FirstLineHasColumnNames = true;
            
        using (var memoryStream = new MemoryStream())
        {
            using (var streamWriter = new StreamWriter(memoryStream))
            {
                var csvContext = new CsvContext();
                csvContext.Write(products, streamWriter);
                    
                streamWriter.Flush();
                    
                context.Response.BinaryWrite(memoryStream.GetBuffer());
            }
        }
    }
}

DotNetZip - Zip Compression and Decompression .NET 4 and Earlier

Quick post about a useful third-party zip compression library if you're working in .NET framework version 4 or earlier.

I am working on a SQL Server 2012 Integration Services (SSIS) package. One of the steps in the package is to decompress a set of zip archives. Unfortunately, .NET script tasks in the SSIS package can only target .NET framework version 4 and earlier. This means that I couldn't make use of the new zip compression classes introduced in .NET 4.5 (see System.IO.Compression).

Fortunately though, there are a handful of open source .NET zip libraries available. The one I opted for is called DotNetZip. DotNetZip has an intuitive API and is working well with a large number of files (I am decompressing approximately 15,000 archives). The library is available as a NuGet package. The two snippets below show just how easy it is to compress and decompress files using zip.

To compress a file into a zip archive:

using (var zipFile = new ZipFile())
{
    // The empty string parameter ensures the file is archived to the 
    // root of the archive
    zipFile.AddFile(@"C:\Test\Data.txt", string.Empty);
    zipFile.Save(@"C:\Test\Data.zip");
}

To decompress files out of a zip archive:

using (var zipFile = new ZipFile(@"C:\Test\Data.zip"))
{
    zipFile.ExtractAll(@"C:\Test\Output");
}

CsQuery - JQuery for .NET

I'm currently working on a personal use utility application which requires some web scraping to extract data (from HTML) which can be locally processed by the application. Getting the raw HTML was straightforward enough using the HttpWebRequest and HttpWebResponse classes in the System.Net namespace.

I then reached the point where I had some raw HTML in a string that I needed to parse. After doing a quick search I found CsQuery (available as a NuGet package) which is an open source JQuery port for .NET. I was able to easily extract the data I required from the HTML using the familiar JQuery-like selectors. There is an example code snippet below which shows just how easy it is to use CsQuery.

var html = new StringBuilder();
html.Append("<html><body>");
html.Append("<h1>Hello, world!</h1>");
html.Append("<p class='intro'>This program is using CsQuery.</p>");
html.Append("<p id='author'>CsQuery is a library written by James Treworgy.</p>");
html.Append("</body></html>");

var dom = CsQuery.CQ.Create(html.ToString());

// Get the inner text of an element by element name selector
Console.WriteLine(dom["h1"].Text());

// Get the inner text of an element by class name selector
Console.WriteLine(dom[".intro"].Text());

// Get the inner text of an element by id selector
Console.WriteLine(dom["#author"].Text());

// Add a class to an element
dom["h1"].AddClass("title");
            
// Update the title text using new class in selector
dom[".title"].Text("CSQuery - a JQuery port for .NET");

// Now retrieve the new title by a class selector
Console.WriteLine(dom[".title"].Text());

// Pause console
Console.ReadLine();

The example source code is available in a C# console application project on GitHub - https://github.com/rsingh85/CsQueryExample.

The ExpandoObject Stringified

I had a requirement to output some data as part of a number of pages in an e-commerce site. This data would change from page to page and typically get richer as a user would go through an order path in the application. The data needed to be in JSON format and was going to be used by the marketing guys to help track information about user behaviour across the order process. The data was also subject to change regularly depending on what the marketing team wanted to track. In short, I had to construct a JSON string on the server side in C#.

I had seen something like this done before where a StringBuilder was used to construct a large JSON string which was then pushed out in the response with the rest of the page markup. This approach seemed messy and difficult to maintain. I did a bit of research on some approaches to constructing a potentially complex and changing JSON object using C# and came across the ExpandoObject class. MSDN has a nice succinct explanation of ExpandoObject:

"Represents an object whose members can be dynamically added and removed at run time."

You can find this class in .NET 4 in the System.Dynamic namespace. ExpandoObject lets you effectively "model" an object on the fly with properties that don't really exist (just like using the ViewBag in ASP.NET MVC). In my case, it saved me from writing a number of classes or complex strings just to hold data that was to be output in page responses. Instead, I could use ExpandoObject and then use a JSON serializer to stringify the object.

The example below shows how easy and flexible it is to use ExpandoObject with the Newtonsoft .NET JSON library (available as a NuGet package):

dynamic orderInfo = new ExpandoObject();

orderInfo.OrderDate = DateTime.Today;

orderInfo.ProductTypesAdded = new List<dynamic>();
orderInfo.ProductTypesAdded.Add("Radio");
orderInfo.ProductTypesAdded.Add("Television");
orderInfo.ProductTypesAdded.Add("Recorder");

orderInfo.ReachedCheckout = true;
orderInfo.PaymentMethod = "Card";
            
orderInfo.DeliveryInfo = new ExpandoObject();
orderInfo.DeliveryInfo.Method = "First";
orderInfo.DeliveryInfo.Country = "UK";

var json = JsonConvert.SerializeObject(orderInfo);

The resulting JSON is:

{
    "OrderDate":"2013-10-11T00:00:00+01:00",
    "ProductTypesAdded":[
        "Radio",
        "Television",
        "Recorder"
    ],
    "ReachedCheckout":true,
    "PaymentMethod":"Card",
    "DeliveryInfo":{
        "Method":"First",
        "Country":"UK"
    }
}

C# MongoDB Repository Implementation

I recently started a small project with a friend and we opted for MongoDB as our data store. One of the initial tasks was to write a repository class that allowed us to store, retrieve, update and search for entities in MongoDB. In the past, I've worked on codebases where there was one repository per entity, it didn't take long to discover that this resulted in a lot of code duplication across the data layer. So the goal here was to write the repository generically enough so that we only have one implementation that can be reused for any entity within our application. This meant that each entity would have its own MongoDB collection (if you're not familiar with MongoDB, a collection can be thought of as a table in the relational world - see this page for a comparison).

One of the first steps in this task was to write an interface for the repository - this is in case we decide to use a different data store in the future. A while back, I found a repository interface on the Redmondo blog which covers everything I'd want from a repository, so we'll use a slightly modified version of that interface (I've removed comments for brevity, you can download the code using a link further below and that'll contain the comments):

public interface IRepository<TEntity> where TEntity : EntityBase
{
    bool Insert(TEntity entity);
    bool Update(TEntity entity);
    bool Delete(TEntity entity);
    IList<TEntity>
        SearchFor(Expression<Func<TEntity, bool>> predicate);
    IList<TEntity> GetAll();
    TEntity GetById(Guid id);
}

To paraphrase the code, this is a generic repository interface for an entity of type TEntity that must derive from a base class called EntityBase. The EntityBase class is a very simple abstract class and contains just one property, the identifier property:

/// <summary>
/// A non-instantiable base entity which defines 
/// members available across all entities.
/// </summary>
public abstract class EntityBase
{
    public Guid Id { get; set; }
}

The idea is for any entity that we want to manage in our data store, that entity must derive from EntityBase. So the infrastructure is all in place for our "MongoDbRepository". I used the official 10gen MongoDB C# driver (available as a NuGet package) and arrived at the following repository implementation:

/// <summary>
/// A MongoDB repository. Maps to a collection with the same name
/// as type TEntity.
/// </summary>
/// <typeparam name="T">Entity type for this repository</typeparam>
public class MongoDbRepository<TEntity> :
    IRepository<TEntity> where
        TEntity : EntityBase
{
    private MongoDatabase database;
    private MongoCollection<TEntity> collection;

    public MongoDbRepository()
    {
        GetDatabase();
        GetCollection();
    }

    public bool Insert(TEntity entity)
    {
        entity.Id = Guid.NewGuid();
        return collection.Insert(entity).Ok;
    }

    public bool Update(TEntity entity)
    {
        if (entity.Id == null)
            return Insert(entity);
       
        return collection
            .Save(entity)
                .DocumentsAffected > 0;
    }

    public bool Delete(TEntity entity)
    {
        return collection
            .Remove(Query.EQ("_id", entity.Id))
                .DocumentsAffected > 0;
    }

    public IList<TEntity>
        SearchFor(Expression<Func<TEntity, bool>> predicate)
    {
        return collection
            .AsQueryable<TEntity>()
                .Where(predicate.Compile())
                    .ToList();
    }

    public IList<TEntity> GetAll()
    {
        return collection.FindAllAs<TEntity>().ToList();
    }

    public TEntity GetById(Guid id)
    {
        return collection.FindOneByIdAs<TEntity>(id);
    }

    #region Private Helper Methods
    private void GetDatabase()
    {
        var client = new MongoClient(GetConnectionString());
        var server = client.GetServer();

        database = server.GetDatabase(GetDatabaseName());
    }

    private string GetConnectionString()
    {
        return ConfigurationManager
            .AppSettings
                .Get("MongoDbConnectionString")
                    .Replace("{DB_NAME}", GetDatabaseName());
    }

    private string GetDatabaseName()
    {
        return ConfigurationManager
            .AppSettings
                .Get("MongoDbDatabaseName");
    }

    private void GetCollection()
    {
        collection = database
            .GetCollection<TEntity>(typeof(TEntity).Name);
    }
    #endregion
}

In case you're interested, a while ago I wrote a separate blog post on how to perform CRUD operations against MongoDB using the C# driver. To use the repository implementation, you'll need two application configuration settings defined - one that stores the name of the MongoDB database and the other that contains the MongoDB connection string (with a placeholder for the database name). You should have something like:

<appSettings>
  <add key="MongoDbDatabaseName" value="MyCarsDatabase" />
  <add key="MongoDbConnectionString"
         value="mongodb://localhost/{DB_NAME}?safe=true" />
</appSettings>

Hopefully this repository is useful to someone else who is working with MongoDB in C#. Any questions or suggestions for improvements are always welcome via comments. The source code is available on GitHub - https://github.com/rsingh85/MongoDbRepository.

Aspect-Oriented Programming in C# with PostSharp - Logging Aspect Example

I was looking at some code in a class library project with a colleague recently. One thing that stood out was that a lot of methods across the various classes in the library were using a "Logger" class to persist runtime information (things like actual parameters and exception messages). There was a clear pattern in how these methods were structured, they logged the fact that they were called (with parameter information) and then had logic specific to what they were supposed to do. Any exceptions raised by the main logic of the methods were also logged. The "Logger" instance was not being injected into each of these classes, it was a concrete implementation without an interface. In the end, we came to the conclusion that we could improve this code as follows:

• We could de-couple the logger from all the classes by using dependency injection. This would involve creating an interface for the logger, ensuring the current logging class implements this interface and then rearchitecting the classes that use the logger so that they are IoC friendly. An IoC container such as Ninject could then be used to inject a specific implementation of the logger into the various classes at runtime.
• Or, we can make use of Aspect-Oriented Programming (AOP)

The latter of these points is the subject of this blog post. AOP is a programming paradigm just like Object-Oriented Programming (OOP). But instead of focusing on classes, objects and methods - AOP focuses more on separating concerns through "aspects". AOP typically deals with concerns that "cross-cut" a codebase. Luckily for us, the most popular example of a cross-cutting concern seems to be logging. As my colleague and I witnessed in the class library project, logging was being applied across a number of classes, therefore tightly coupling the logger with these classes. Furthermore, it was clear that each method that was logging wasn't adhering to the single responsibility principle.

The goal was therefore to seperate these concerns in a clean way. AOP enables this by letting you implement cross-cutting concerns as aspects which are then applied to existing code through aspect weaving. The C# programming language doesn't have any first-class support for AOP as it is primarily an OOP language. But there are libraries that allow you to apply AOP concepts using existing C# language constructs. One such library is PostSharp, which makes it easy to write an aspect and then apply the aspect to existing code. In the example below, we'll make use of PostSharp to write an aspect for logging method call information to the debug output.

PostSharp Logging Aspect Example

The PostSharp library allows you to define aspects as standard C# attributes. You can do this by deriving from one of the aspect classes from the library and override the methods that are of interest to your aspect. In the logging aspect example below, we derive from the PostSharp.Aspects.OnMethodBoundaryAspect class and override the OnEntry, OnExit and OnException methods.

[Serializable]
public class LogAspectAttribute : OnMethodBoundaryAspect
{
    private Guid _methodCallIdentifier;
               
    public override void OnEntry(MethodExecutionArgs args)
    {
        _methodCallIdentifier = Guid.NewGuid();

        Debug.WriteLine("{0} - Entering method {1} with arguments: {2}",
            _methodCallIdentifier,
            args.Method.Name,
            string.Join(", ", args.Arguments));
    }

    public override void OnExit(MethodExecutionArgs args)
    {
        Debug.WriteLine("{0} - Exited method {1}",
            _methodCallIdentifier,
            args.Method.Name);
    }

    public override void OnException(MethodExecutionArgs args)
    {
        Debug.WriteLine("{0} - Method {1} raised exception with message: {2}",
            _methodCallIdentifier,
            args.Method.Name,
            args.Exception.Message);
    }
}

Note that PostSharp contains a number of predefined aspect classes that you can derive from depending on your particular use case. For instance, the class PostSharp.Aspects.MethodInterceptionAspect is particularly useful for implementing security on methods (i.e. you can decide in your aspect whether to allow the intercepted call to proceeed through).

Back to the example above, the OnEntry method is called just before the target method (the method that we'll annotate with this attribute) is called. The OnExit method is called once the target method completes executing and the OnException method is called if the target method raises an exception. Each of these three methods provide useful points for us to do some logging. The MethodExecutionArgs instance passed to each method also contains some useful context information for us to add to the log.

To now use this aspect, it's a simple case of annotating the methods you want to log with the [LogAspect] attribute, as shown below.

[LogAspect]
void SayHelloToWithoutException(string name)
{
    Console.WriteLine("Hello, {0}!", name);
}

[LogAspect]
void SayHelloToWithException(string name)
{
    Console.WriteLine("Hello, {0}!", name);
    throw new Exception("Oops! Something went wrong...");
}

The logging logic is now neatly encapsulated in one location. If we call the two methods above, one after the other, we'll get the debug output:

10 C#/.NET Features You May Not Know About

I thought it would be useful to document some of the typically lesser known features of the C# programming language and the .NET framework as a series of posts. Some of these features I've found useful and others I probably just haven't found a suitable use case for yet.

1. Anonymous Code Scopes in Methods

It's possible to have anonymous inner scopes within your method definitions. (I'm yet to come across a non-contrived use case for this!)

void MethodWithAnonymousScope()
{
    var helloPart = "Hello";

    {
        var worldPart = "world";
        Console.WriteLine("{0} {1}", helloPart, worldPart);
    }

    // "worldPart" doesn't resolve in this scope
}

2. Increment/Decrement Operator Position Significance

The position of the increment (++) and decrement (--) operators is significant. In the example below, when the increment operator is used as a postfix, it returns the value of 'number' before it has been incremented. Conversely, the prefix increment operator returns the value after it has been incremented. The decrement operator works with the same logic but decrements the number.

void PlusPlusOperator()
{
    var number = 0;

    Console.WriteLine(number++); // Outputs zero
    Console.WriteLine(++number); // Outputs two
}

3. The Default Keyword

The default keyword is a neat way to get the default value for a specified type. It's especially useful when working in a generic context.

void DefaultKeyword()
{
    var intDefault = default(int); // default(int) == 0
    var boolDefault = default(bool); // default(bool) == false

    // default(string) == null (as for all reference types)
    var stringDefault = default(string); 
}

4. Null-Coalescing Operator

The null-coalescing operator (??) provides a succinct way of returning a default value if your reference or nullable-value type is null. In the following example, if myNullableInteger (left operand) is not null, then it's returned, else the default value for int is returned (right operand).

int NullCoalescingOperator()
{
    int? myNullableInteger = SomeMethodThatCouldReturnNull();
    return myNullableInteger ?? default(int);
}

5. Short-Circuit Evaluation with Boolean Operators

The logical AND (&&) and OR (||) operators are short-circuit evaluated (left to right). For example, if the left operand of a logical AND is false, the right operand is not evaluated (as the whole condition will always be false). Similarly, if the left operand of a logical OR is true, the right operand is not evaluated. This can be demonstrated by observing the output of:

void ShortCircuitEvaluation()
{
    bool result;
            
    result = LeftOperand(true) || RightOperand(false);
    result = LeftOperand(false) || RightOperand(true);
    result = LeftOperand(true) && RightOperand(false);
    result = LeftOperand(false) && RightOperand(true);
}

bool LeftOperand(bool value)
{
    Console.WriteLine("Left operand evaluated");
    return value;
}

bool RightOperand(bool value)
{
    Console.WriteLine("Right operand evaluated");
    return value;
}

It's useful to know this so that you can safely perform multiple tests in a single if statement. In the example below, if myObject is null, the right operand is not evaluated (which is good because it'd cause a NullReferenceException).

if (myObject != null && myObject.SomeProperty == SomeValue)
    ...

Also note that if you use a single '&' and single '|' you bypass short-circuit evaluation and force the entire condition to be evaluated.

6. Aliases for Generic Types

You can assign an alias to a namespace but you can also assign an alias to a specific generic type to save yourself from typing the awkward generic syntax over and over again (especially useful when working with key/value pair based generic types where the value may also be a key/value pair!).

using StringList = System.Collections.Generic.List<string>;
...
void GenericAliases()
{
    // Can use the alias "StringList"
    // instead of List<string> 

    var stringList = new StringList();
    stringList.Add("Hello");
    stringList.Add("World");
    stringList.ForEach(Console.WriteLine);
}

7. Extension Methods on Dynamic Types

I came across this one when working with the dynamic ViewBag in ASP.NET MVC. As the title states, you cannot invoke an extension method on a type (that has the extension method defined for it and is in scope) which is dynamically typed. I have documented this one in this post (click to view). As the post shows, you have to call your extension method in the same fashion as you would call a standard static method, then pass your dynamically typed variable in as a parameter to the extension method.

8. System.String supports an Indexer

The string class has a readonly (get) char indexer defined on it, thus allowing you to access characters in the string using a zero-based index.

void StringIndexer()
{
    string message = "Hello, world!";

    for (int i = 0; i < message.Length; i++)
    {
        Console.WriteLine(message[i]); 
    }
}

9. Using foreach with System.String

The string class implements the IEnumerable<char> interface, which means that you can use the foreach statement on a string to enumerate through each character.

void ForeachWithString()
{
    string message = "Hello, world!";

    foreach (char character in message)
    {
        Console.WriteLine(character);
    }
}

10. Introspecting Code with Expression Trees

The System.Linq.Expressions.Expression class enables you to represent a code expression in a tree-based data structure that can then be used for introspection. This is a powerful feature which also then enables code modification in the expression tree (at runtime) and then subsequent compilation and execution.

The following example shows how we can wrap a simple lambda expression into an Expression, introspect the expression, compile the expression (in this case returning a Func<int, int, int>) and then execute the expression.

void Expressions()
{
    Expression<Func<int, int, int>> addExpression = (a, b) => a + b;

    foreach (var param in addExpression.Parameters)
    {
        Console.WriteLine(
            "Func Param Name: {0}, Param Type: {1}", 
            param.Name, 
            param.Type);
    }

    Console.WriteLine("Func return type: {0}", 
        addExpression.ReturnType);

    Console.WriteLine("10 + 20 = {0}", 
        addExpression.Compile()(10, 20));
                        
    // Can also use the Invoke method on the returned Func<...>
    // to aid readability
    // e.g. addExpression.Compile().Invoke(10, 20);
}

You may have indirectly used expression trees if you're an ASP.NET MVC developer. The HTML helper classes make extensive use of them, for example, the Html.TextBoxFor method has an overload that accepts a single parameter of type Expression<Func<dynamic, dynamic>>. An example call to this method would be @Html.TextBoxFor(m => m.FirstName) where 'm' is an instance of your view model. The TextBoxFor method uses the supplied expression (a lambda) to construct the HTML that is put back into the view. In this case it outputs an input element with an id and name attribute value of "FirstName" - which was retrieved using introspection (made possible with expression trees).

Mocking Objects with Moq

A friend recently told me that his development team is trialing test-driven development on a new project and he asked me to recommend a mocking library for them to try. I recommended Moq (also available as a NuGet package). I have been using Moq as my go-to mocking library in C# for well over a year now. Having had experience with a couple of other mocking libraries prior to Moq, I can testify to its widely reported ease of use. It has a very neat fluent API that results in easy to understand code.

If you are new to the idea of mocking, then think of it as a way to simulate (or "mock") the behaviour of an object, where you can control exactly how you want the mocked object to behave. The mocked object can simulate a class that you have written from scratch or it can even simulate a class that you don't have the source code for (e.g. a BCL class).

A good example of when you would want to mock an object is when you are writing a unit test. Let's imagine that your unit test is exercising a method called RegisterUser on your UserService class. The UserService class constructor accepts an interface called IEmailService as one of its parameters. The IEmailService defines one method called SendRegSuccessEmail (which returns a boolean that indicates whether the email was fired off successfully). The RegisterUser method accepts two parameters, an email and a password and returns a boolean that indicates if registration was successful. The implementation of this method checks if the supplied email already exists, if it doesn't, then it saves the email and password in some repository, sends an e-mail to the user telling them that their registration was successful and returns true. If registration fails (e.g. if the user already exists in the repository) then false is returned.

With this setup, imagine that you now wanted to write a unit test that tests whether the RegisterUser method prevents multiple registrations for a single email. As the developer of the RegisterUser method, you know that it uses the IEmailService to fire off an e-mail - and that you (obviously) don't want to fire off e-mails in your unit test. This is where mocking comes into play. You can setup your test so that you mock an implementation of the IEmailService interface and control how you want the SendEmail method to behave. Using the Moq library, your setup would look like:

var emailServiceMock = new Mock<IEmailService>();
 emailServiceMock
   .Setup(es => es.SendRegSuccessEmail(It.IsAny<string>()))
     .Returns(true);

var userService = new UserService(emailServiceMock.Object, ...);

// Test userService.RegisterUser(...)

You can now write the remaining bit of your unit test using the userService object with the knowledge that you'll never fire off unnecessary e-mails when calls are made to the IEmailService.SendEmail method. As can be seen in the snippet above, it is quite simple to setup a mock, you instantiate an instance of the generic Mock class and pass in the object-to-mock as a type parameter (in this case IEmailService). The next line tells the mock object that whenever the SendRegSuccessEmail method is called with any string parameter (It.IsAny<string>()), then return the boolean value true. You can try this for yourself and you'll find that the following expression will always equal true:

emailServiceMock.Object.SendRegSuccessEmail("foo@bar.com")

Once the mock object is setup, you can get the actual mocked object instance using the "Object" property on the Mock class - the returned instance from this property can then be used in any location that it is expected (in the snippet, we've passed the mocked instance into the UserService constructor). The RegisterUser method will therefore use this mock and we'll avoid the unwanted scenario of emails getting fired off whenever our unit tests are executed!

Highcharts JS Library - Overlapping Points

I'm currently working on a small ASP.NET MVC4 application that reports some live numerical data in a chart. My manager pointed me to Highcharts JS which is a neat and simple to setup library. The particular chart type we chose to use was this.

The chart sits in its own partial view. It is periodically polling an action that returns data in JSON format for it to plot along an X-axis representing time. If you take a look at the JavaScript for the demo of the chart we decided to use (link above), it has two places where points are plotted.

Firstly, it plots points when you define a series for the chart - this is where I am plotting all the initial data accumulated since the view was requested by a user. Then, I'm plotting any subsequent data that has just been accumulated using a timer that is defined in the load event for the chart (this is the part that polls the action I mentioned earlier).

When plotting the chart in this way, I ran into an issue when we had no initial data to plot. In this scenario, the chart initially (and correctly) displays as empty. However, as data was coming in from my timer calls to the action - only one point would ever be plotted. After investigating this, it turned out that it was because I was passing in the boolean value true for the "shift" parameter to the Series.addPoint function.

This parameter tells the chart library to shift the graph to the left (thus removing the left-most plot) and hence my last plotted point was always being lost on each poll to the action. This in-turn gave the illusion that my points were being overwritten. To fix this, I passed in a boolean expression that tests if the series has 30 points plotted - this ensured that the chart always displays 30 plotted points at the most and resolved the problem of "overwriting" plotted points!

CRUD against MongoDB via C#

In my previous post, I gave some of my first thoughts about NoSQL in relation to MongoDB. In this post we will look at how you can perform basic CRUD operations against a MongoDB collection using the official C# driver. The purpose of this post is for me to use it as a handy reference when working with MongoDB in the future - hopefully you'll also find it useful. I will assume that the reader has some familiarity with using MongoDB on the shell.

Throughout the post I'll be using a simple collection of documents where each document stores some basic information about an aircraft. If you load the MongoDB shell and execute the following statements then we'll have a common ground to start with:

db.planes.insert({
    'Manufacturer':'Lockheed Skunk Works',
    'Model':'Blackbird SR-71',
    'FirstFlight': new Date('12/22/1964')
})
db.planes.insert({
    'Manufacturer':'Lockheed Skunk Works',
    'Model':'X-55 ACCA',
    'FirstFlight': new Date('06/02/2009')
})

At this point, you should have a database called mongotest with one collection containing two JSON documents. You can verify this by executing:

db.planes.find().pretty()

We'll now access and modify the planes collection using the C# driver. You can download the driver from here or add it to your solution using the NuGet package (it's easy to do using the NuGet package manager in Visual Studio). For this post, I'm using version 1.6.1 of the official MongoDB C# driver. Assuming you now have added references to MongoDB.Bson.dll and MongoDB.Driver.dll, add the following three using statements at the top of your class (FYI, I practiced with a standard console application directly within the Main method):

using MongoDB.Bson;
using MongoDB.Driver;
using MongoDB.Driver.Builders;

Now we can define a class that will map to a single plane document. We will use this class along with the MongoDB generic C# driver methods to insert, retrieve, update and remove documents from our planes collection.

public class Plane
{
    public ObjectId Id { get; set; }
    public string Manufacturer { get; set; }
    public string Model { get; set; }
    public DateTime FirstFlight { get; set; }
}

Note how we're using the MongoDB.Bson.ObjectId type for our identifier property (we're relying on MongoDB to add unique id's to newly inserted plane documents). Also note that the Plane class must support a parameterless constructor for the driver to be able to work with it.

Let's now take a look at how you can insert a new plane document into the planes collection using the driver. We'll first get a handle on the planes collection, I have the following four lines at the top of my Main method that gives me the required reference (planesCollection):

var connectionString = "mongodb://localhost/?safe=true";
var server = MongoServer.Create(connectionString);
var mongotestdb = server.GetDatabase("mongotest");
var planesCollection = mongotestdb.GetCollection<Plane>("planes");

To insert a new document into the planes collection (note that the Id property will be filled-in by the insert method):

planesCollection.Insert(new Plane {
    Manufacturer = "Unknown",
    Model = "Tornado IDS/ECR",
    FirstFlight = new DateTime(1974, 8, 14)
});

To retrieve a list of all the documents in the planes collection:

var planes = planesCollection.FindAll().ToList();

To retrieve a list of filtered documents - let's say we want only the planes that are manufactured by Lockheed:

var lockheedPlanes = planesCollection.Find(
    Query.EQ("Manufacturer", "Lockheed Skunk Works"))
        .ToList();

To update a document (as a whole block) in the planes collection:

var planeToUpdate = planesCollection.FindOne(
    Query.EQ("Manufacturer", "Unknown")
);
planeToUpdate.Manufacturer = "Panavia Aircraft GmbH";
planesCollection.Save(planeToUpdate);

Note that you can also perform a partial update to a document (not as a block), refer to the Update method on the MongoCollection class.

Finally, to remove a set of documents based on a query from the planes collection - in this case we'll remove all planes manufactured by Lockheed from the collection:

planesCollection.Remove(
    Query.EQ("Manufacturer", "Lockheed Skunk Works")
);

NDataFlow - Open Source .NET Dataflow Library

Last year, a colleague of mine showed me an open source .NET extract, transform and load (ETL) helper library that he's working on. It is called NDataFlow and allows you to annotate methods with attributes to create a dataflow in your application. It's a nice lightweight library that you can use whenever you are developing simple or complex ETL programs. The example below simulates a very simple ETL scenario where a set of people (hard-coded in the example) are filtered based on their location and then output to a file.

class Program : DataflowComponent
{
  static void Main(string[] args)
  {
    new Program().Run();
  }

  //First method in the flow
  [Operation]
  public void DataSource(Output output)
  {
    //Imagine retrieving people from a real data source
    //e.g. database, xml file, csv file, etc.
    output.Emit(new Person() { Name = "Alice", City = "London" });
    output.Emit(new Person() { Name = "Bob", City = "New York" });
    output.Emit(new Person() { Name = "Foo", City = "London" });
    output.Emit(new Person() { Name = "Bar", City = "Sydney" });
  }

  [Operation]
  public IEnumerable FilterForLondonPeople
    ([Link("DataSource")] IEnumerable input)
  {
    return input.Where
      (p => p.City.Equals("London", 
        StringComparison.InvariantCultureIgnoreCase));
  }

  [Operation]
  public void OutputResults
    ([Link("FilterForLondonPeople")] IEnumerable results)
  {
    using (var sw = new StreamWriter(@"C:\LondonPeople.txt", false)
    {
      foreach (var p in results)
        sw.WriteLine("{0} {1}", p.Name, p.City);
    }
  }
}

The example shows that there is little work needed to get a simple dataflow setup and running. You inherit the Run method by deriving from the NDataFlow.DataflowComponent class. Then, if you've setup your method and attributes correctly using the LinkAttribute it's a simple case of calling Run to start your dataflow. In this case, the first method in the dataflow would be DataSource, whose output is sent to FilterForLondonPeople and finally whose output is sent to the OutputResults method.

C# How To: JSON Serialisation and Deserialisation

I've started to make an active effort in using JSON over XML, the main reason being that I find JSON formatted data to be easier on the eye than XML formatted data. I found a project in our source control repository at work that used JSON formatted data as input. The project used a neat little JSON library that I'll now be using whenever required. The library is called Json.NET. The following code shows how easy it is to serialise a .NET POCO into JSON, and then reconstruct the object back from JSON using the aforementioned library.

Imagine we have a simple class that models a person:

internal class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }
}

We can create an instance of this class and then serialize the object into a JSON string using the JsonConvert class as follows:

var inputPerson = new Person() 
    { FirstName = "Alan", LastName = "Turing", Age = 41 };

string json = JsonConvert.SerializeObject(inputPerson);

The json string variable now contains the value:

{"FirstName":"Alan","LastName":"Turing","Age":41}

Reconstructing the object back from a JSON string is as simple as:

var outputPerson = JsonConvert.DeserializeObject<Person>(json);