Domain Driven Design with Web API extensions part 10: the MongoDb context

December 10, 2015 Leave a comment

Introduction

In the previous post we installed MongoDb locally. We also started the MongoDb server and connected to it with a client. We then inserted a test console application into our DDD skeleton project, imported the MongoDb .NET driver and connected to the MongoDb server using the driver.

In this post we’ll continue to explore the MongoDb context and some practical limitations compared to the automated tools available in EntityFramework. We’ll also add a new C# console library to the DDD skeleton project. The new library will eventually contain the MongoDb equivalent classes of what we have in the WebSuiteDemo.Loadtesting.Repository.EF layer.

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Customise your list by overriding Collection of T with C# .NET

December 9, 2015 Leave a comment

Imagine that you’d like to build a list type of collection where you want to restrict the insertion and/or deletion of items in some way. Let’s say we need an integer list with the following rules:

  • The allowed range of integers is between 0 and 10 inclusive
  • A user should not be able to remove an item at index 0
  • A user should not be able to remove all items at once

One possible solution is to derive from the Collection of T class. The generic Collection of T class in the System.Collections.ObjectModel namespace provides virtual methods that you can override in your custom collection.

The virtual InsertItem and SetItem methods are necessary to control the behaviour of the Collection.Add and the way items can be modified through an indexer:

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Resolving null values in C#

December 8, 2015 1 Comment

Say you have a method which accepts a string parameter. The method may need to handle null values in some way. One strategy is to validate the parameter and throw an exception:

private static string Resolve(string input)
{
	if (input == null) throw new ArgumentNullException("Input");
.
.
.
}

Another strategy is to provide some default value with an if-else statement:

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Domain Driven Design with Web API extensions part 9: setting up MongoDb

December 7, 2015 1 Comment

Introduction

In the previous post we set out the main topic of this new extension to the DDD model project. We said that we would add another repository mechanism, namely MongoDb. We went through the basic idea and some terminology behind MongoDb, e.g. what a document, a collection or an object ID means.

In this post we’ll set up MongoDb locally and try to connect to it from .NET using the MongoDb .NET driver.

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Python language basics 70: starting with classes

December 6, 2015 1 Comment

Introduction

In the previous post we extended the topic of comprehensions and looked at comprehension filters. We saw that it was really easy to extend the standard comprehension “formula” with an if-clause. The filter is then applied to every element in the iteration and the comprehension function only considers those elements that pass the boolean test.

In this post we’ll start looking at something completely different: classes. Classes are probably the most important building blocks of object oriented languages.

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Python language basics 69: filtering comprehensions

December 5, 2015 1 Comment

Introduction

In the previous post we discussed how to iterate over a dictionary with the concise comprehension syntax. We saw that it wasn’t very different from how list comprehensions are written.

In this post we’ll look at how to attach a conditional clause to a comprehension function.

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How to create custom string formatters with C# .NET

December 4, 2015 Leave a comment

.NET has a fairly large number of built-in string formatters that you can pass into the string.Format method. Here are some examples from the MSDN page about formatting:

String.Format("{0,-12}{1,8:yyyy}{2,12:N0}{3,8:yyyy}{4,12:N0}{5,14:P1}",
                                city.Item1, city.Item2, city.Item3, city.Item4, city.Item5,
                                (city.Item5 - city.Item3)/ (double)city.Item3);
String.Format("{0,-12}{1,8}{2,12}{1,8}{2,12}{3,14}\n",
                                    "City", "Year", "Population", "Change (%)");
String.Format("{0,-10:C}", 126347.89m);

The IFormatProvider and ICustomFormatter interfaces will provide you with the methods required to create your own formats.

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Domain Driven Design with Web API extensions part 8: domain repository with MongoDb

December 3, 2015 1 Comment

Introduction

Some months ago we went through an updated series on Domain Driven Design starting with this post. We built a functioning skeleton project with EntityFramework as the backing store, a Web API layer as the top consumer, a loosely coupled service layer and a central domain layer with some logic.

In this extension series we’ll investigate how to implement the domain repository in a data store that’s markedly different from SQL Server. In particular we’ll take a look at the NoSql document-based MongoDb.

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Type conversion example in C# .NET using the IConvertible interface

December 2, 2015 1 Comment

In this we saw how to convert between numeric types explicitly and implicitly. There are other ways to implement conversions in C#. You must have come across the System.Convert static methods such as System.ConvertToInt32 or System.ConvertToByte.

You can implement your own conversions by implementing the IConvertible interface. Consider the following object:

public class House
{
	public double Area { get; set; }
	public int NumberOfRooms { get; set; }
	public string Address { get; set; }
	public bool ForSale { get; set; }
        public DateTime DateBuilt { get; set; }
}

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Keyword function arguments in C#

December 1, 2015 Leave a comment

In this post we’ll quickly go through positional vs. keyword function arguments in C#.

Say you have the following function:

public string GetContent(bool base64encode, bool compress, bool withUniqueId, string filename, int maxSize)
{
	return string.Empty;
}

You’ll learn very early in your programming class that you can call a function by supplying the arguments in exactly the same order as they are listed in the method signature. Here’s an example:

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