Really weird C# code

My ServiceLocator (which has been further updated since my last post on it, so on the off chance that anybody wants the latest version, leave me a comment) can only register functions with no parameters - Func<T>. What happens if one wants to register a function with one or more parameters?

As an example, let's say that I have many possible connection strings, and in some cases when I want an instance of DataContext I have to initialize it with one of those. Since my ServiceLocator doesn't accept functions with parameters, I cannot write

    var dc = ServiceLocator.GetInstanceOf<DataContext>(connectionString);

Here's a way of transforming a function with parameters to one without: create a function that returns the original function. That is, given

    Func<T1, T> f;

I need another function that will return f:

    Func<Func<T1, T>> g = () => (a) => f(a);

So, in order to register my DataContext I am now going to use the following syntax:

    Bind<Func<string, DataContext>>.To(() => (connectionString => new DBDataContext(connectionString)));

and to retrieve the instance and initialize it correctly, I must use:

    var dc = ServiceLocator.GetInstanceOf<Func<string, DataContext>>()(connectionString);

Not extremely clear, so some helper functions (and confining in a library of sorts) are probably needed.

Edit: I just made a change to the ServiceLocator code; one can now write:

    var dc = ServiceLocator.GetInstanceOf<string, DataContext>("connectionString");

This is the overload for one argument:

    public static T GetInstanceOf<T1, T>(T1 arg1) where T : class  
    {  
      return GetInstanceOf<Func<T1, T>>()(arg1);  
    }

I only have 3 overloads (up to Func<T1, T2, T3, T>) but that should be enough for anything I might need in the foreseeable future. Oh, and I can still have / use the initial binding too (the one with no connection string). Cool :)

Comments

Post a Comment

Popular posts from this blog

Posting dynamic Master / Detail forms with Knockout

Image
I have the following dynamic form in my GitHub Inventory project : I created the form with KnockoutJS , using some ideas from this article . The detail view looks like this: <table id="acquisition_items" class="jtable"> <thead> <tr> <th>Product Name</th> <th>Quantity</th> <th>Price</th> <th>Value</th> <th><button data-bind="click: addItem">[+]</button></th> </tr> </thead> <tbody data-bind="foreach: items"> <tr> <td> <input data-bind="value: ProductName" type="text" value="" /> </td> <td> <input data-bind="value: Quantity" type="text" value="" /> </td> <td> ...
Read more

Comparing Excel files, take two

Image
I already wrote this project once, on GitHub , but I can't say that I like the result. I wrote that code without TDD, mostly to see if I can still work in the "normal" fashion. I can, but I had a bug that took me a while to even discover and then was difficult to write tests for. I also hate the temporal dependency in that design (if you don't call the SortBy method first, the ExcludeRecords method will return incorrect results). Anyway; here's attempt number two, writing that code using TDD. Structure I start by creating my usual structure for projects of this type - a library for the logic, a console application for the main program and a test project for tests. I also use the Enable NuGet Package Restore option (right-click on the solution node) to add the three NuGet files that will allow someone to automatically download all the packages I'm referencing without wasting space in the source code repository. (Right now I've only added the Moq pa...
Read more

EF Code First: seeding with foreign keys

This is just a quick tip, more for future reference for myself than anything else. When using Entity Framework Code First, one of the things you might want to do while developing the application is to seed your database with some test data. This can be something as easy as: protected override void Seed(InventoryDB context) { context.Products.AddOrUpdate( p => p.Name, new Product { Name = "Hammer", SalePrice = 11.99m, }, new Product { Name = "Nail Pack x100", SalePrice = 0.05m, }, new Product { Name = "Saw", SalePrice = 19.99m, }, new Product { Name = "Toolkit", SalePrice = 39.99m, } ); //... } (I am using the AddOrUpdate method so the code detects whether those products already exist and doesn't add them again if they do.) The Product class is quite simple and – most importantly – doesn't depend on any other: public class Product { public int Id { g...
Read more