Domain Driven Design with Web API extensions part 11: the MongoDb database objects

December 14, 2015 Leave a comment

Introduction

In the previous post we mainly discussed the advantages and limitations of coding against MongoDb using .NET. We also discussed the MongoDb context a little bit and started building the MongoDb version of the repository. We said that there’s not much automation available in the .NET MongoDb driver compared to what you get in EF. However, that’s not necessarily a bad thing since you’re not tied to some “secret” and “magic” underlying mechanism that does a lot of work in the background. Instead you’re free to implement the objects, the rules, the conversions etc. as you wish. It usually means more code, but you get absolute freedom for your repository implementation in return.

In this post we’ll first add a new element to the common infrastructure layer. Then we’ll add the MongoDb database representation of our domain objects.

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Python language basics 72: object initializers and class level properties

December 13, 2015 1 Comment

Introduction

We continued to explore the notion of classes in the previous post. We looked at the difference between constructors and initializers although we haven’t seen the initialisers in action yet. We also built our first class called Person that had one class method called shout. The shout method could be called on an instance of the Person class, i.e. a Person object using the standard dot notation.

In this post we’ll look at the role of initializers and how to supply method arguments to class methods.

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Python language basics 71: continuing with classes

December 12, 2015 2 Comments

Introduction

In the previous post we started discussing classes. We said that classes are the models for objects. The objects are instantiated based on the classes. A class describes the properties for the objects. E.g. a Car class can have a number of variables, such as colour, make, etc. A class can not only contain simple properties, but methods as well, as we’ll see later. Also, a class controls how an object can be instantiated.

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Projection in LINQ C# with the Select operator

December 11, 2015 1 Comment

You can use the Select() extension method in LINQ to create an output of type T from an input sequence of type other than T. Let’s see some examples:

Source data:

string[] bands = { "ACDC", "Queen", "Aerosmith", "Iron Maiden", "Megadeth", "Metallica", "Cream", "Oasis", "Abba", "Blur" , "Chic", "Eurythmics", "Genesis", "INXS", "Midnight Oil", "Kent", "Madness", "Manic Street Preachers", "Noir Desir", "The Offspring", "Pink Floyd", "Rammstein", "Red Hot Chili Peppers", "Tears for Fears", "Deep Purple", "KISS"};

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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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