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For various reasons I would like to not store the connection string for my Entity Framework DB model in one of the various .config files. (I am using the latest and greatest DBContext API with the new Entity Framework version 4.1, .NET 4 and Visual Studio 2010 C#.) However, the code generation template for DBContext only creates a single parameterless constructor. (If I don't use the DBContext API, then my entity framework model has 7 different constructors to chose from, including the one I want.)

The only way I could figure out how to do this was to directly modify the code-generation template (context.tt file) to give me the constructor I want (example code below). This works, but it feels like I'm doing it "the hard way". What is the correct way to get a DBContext constructor that accepts a connection string?

    public <#=Code.Escape(container)#>(string connectionString)
        : base(connectionString)
    {
<#
        WriteLazyLoadingEnabled(container);
#>
    }

One final note in case it might help somebody else. Although this method works, it took me a while to realize that the "connection string" is not strictly the DB connection string, but rather the special entity framework connection string which contains the DB connection string (just like what would be stored in the app.config file).

Keith Morgan
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1 Answers1

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Your approach looks like the most correct way to do this. It's what the t4 templates were created for, and you're basically doing the same thing that the model-first templates do by default.

Another possibility would be to make the db context class be partial (if it isn't by default) and create another partial class file alongside it to add the constructor you want. But it seems likely that you'll want all of your t4-generated contexts to follow this pattern, so I think it's best to leverage the code generation to do this automatically the way you do in the question.

StriplingWarrior
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  • Thanks Helaman for the lightning fast response. I guess I still don't understand why the default template from MS doesn't include all of the different constructors. They are all explicitly mentioned on the EF team blog [link](http://blogs.msdn.com/b/adonet/archive/2011/01/27/using-dbcontext-in-ef-feature-ctp5-part-2-connections-and-models.aspx). But I guess I can live with it if that is how they expect you to do it. I hadn't thought of using a partial class, but that is a reasonable option too. – Keith Morgan Sep 30 '11 at 07:15
  • @ksm: The idea with the code-first templates was to cater to the crowd who were complaining that the edmx-generated code was too bloated. I imagine they figured they'd keep it minimal, and let users modify the t4 if they wanted to add to it. Nice catch on the name reference, btw. – StriplingWarrior Sep 30 '11 at 14:24