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Dependency Injection Containers - Cheat Sheet

01/02/2015

There are a lot of articles out there that describe both Dependency Injection and Inversion of Control. The purpose of this one is to serve as a quick reference for the things I keep forgetting because configuring a DI container is something I do so infrequently. This is a very simple guide showing the easiest scenarios and the simplest syntax. It walks through the same 3 steps:

1. Create Container
2. Configure Container
3. Retrieve from Container

In the following DI libraries:

  • Ninject
  • Unity
  • SimpleInjector
  • StructureMap

Of course it will feature examples tenuously related to animals.

Principals

A Dependency Injection library makes dependency injection easier by doing the work of wiring up an "object graph" (collection of related objects) for your application to use. This is generally done at the entry point to an application:

  • For console apps this is in the main method of Program.cs.
  • For MVC and Web API apps this is in Startup.cs.
  • For class libraries it is difficult to include dependency injection in the library itself as these have no defined entry point. One approach is to rely on the calling application to wire up the dependencies.
  • For WebForms apps it is possible to setup the DI container in the Global.asax Application_Start method however it's a bit more complicated.

Console App Example

In this example we're going to begin building a console app which simulates an ecosystem of toads.

picture of a toad

...

EF7 Table Mapping Exception

15/01/2015

Note: This blog post relates to a library undergoing development and as such the information is likely to become outdated.

Even with Database First through the EDMX gone in Entity Framework 7 it's still possible to work with existing databases.

While trying this out with one of my databases I ran into the following Exception:

<Message>An error has occurred.</Message>

<ExceptionMessage>Invalid object name 'SomeClass'.</ExceptionMessage>

<ExceptionType>System.Data.SqlClient.SqlException</ExceptionType>

<StackTrace>
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction)[...]
</StackTrace>

The Entity Framework "Invalid object name [class name]" exception means that the matching table for one of your classes hasn't been found.

In this case I'm trying to map the SomeClass to the underlying SQL table Map.Test:

[Table("Test", Schema="Map")]
public class SomeClass
{
    public int Id { get; set; }
}

The current version of EF7 (7.0.0-rc1-11953) does not have support for mapping using attributes in this way. Instead one must use Fluent configuration in the DbContext as follows:

public class MyContext : DbContext
{
    public DbSet<SomeClass> SomeClasses { get; set; }

    protected override void OnConfiguring(DbContextOptions options)
    {
        options.UseSqlServer(ConnectionString);
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);

        modelBuilder.Entity<SomeClass>().ForRelational().Table(tableName: "Test", schemaName: "Map");
    }
}

The mapping is configured fluently in the OnModelCreating method. For slightly more useful information about setting EF7 up see this link.

I hope this helps!

...

C# Async for Slugs

07/12/2014

Fun fact for you dear reader, I've not been programming for long, my degree was in Chemistry and though I taught myself a little programming during my degree I was mainly focused on Chemistry. This means I've been programming professionally for less time than C# 5 has been released.

This is why I've found tutorials so far for the Async/Await features in C# 5 (Net 4.5) to be a little lacking, they generally assume the reader has been writing async programs prior to the release of the features.

As a solution to this I've endeavoured to write a guide to async for miserable slugs like myself who have not had exposure to async prior to these keywords.

Demo Scenario

We're going to stick with a very simple console app available on GitHub to make sure all the concepts can be understood by a slug.

Our Program.cs main method is shown below:

public static void Main(string[] args)
{   
    SlugService slugService = new SlugService();
    slugService.GetSlugs(generation: 1);
}

The GitHub version contains a lot more lines which allow the method calls to be timed with the built in stopwatch.

The Slug Service is tasked with retrieving the records of some slugs we've stored somewhere. Let's see what it does:

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