Can I stop the dbml designer from adding a connection string to the dbml file?

Question

We have a custom function AppSettings.GetConnectionString() which is always called to determine the connection string that should be used. How this function works is unimportant to the discussion. It suffices to say that it returns a connection string and I have to use it.

I want my LINQ to SQL DataContext to use this so I removed all connection string informatin from the dbml file and created a partial class with a default constructor like this:

public partial class SampleDataContext
{
    public SampleDataContext() : base(AppSettings.GetConnectionString()) { }
}

This works fine until I use the designer to drag and drop a table into the diagram. The act of dragging a table into the diagram will do several unwanted things:

• A settings file will be created
• A app.config file will be created
• My dbml file will have the connection string embedded in it

All of this is done before I even save the file!

When I save the diagram the designer file is recreated and it will contain its own default constructor which uses the wrong connection string. Of course this means my DataContext now has two default constructors and I can't build anymore!

I can undo all of these bad things but it is annoying. I have to manually remove the connection string and the new files after each change!

Is there anyway I can stop the designer from making these changes without asking?

EDIT

The requirement to use the AppSettings.GetConnectionString() method was imposed on me rather late in the game. I used to use something very similar to what it generates for me. There are quite a few places that call the default constructor. I am aware that I dould change them all to create the data context in another way (using a different constructor, static method, factory, ect..). That kind of change would only be slightly annoying since it would only have to be done once. However, I feel, that it is sidestepping the real issue. The dbml file and configuration files would still contain an incorrect, if unused, connection string which at best could confuse other developers.

Answer 1

You could use something like SqlMetal to generate your own DataContext designer file, but you're right - the DataContext by default is pretty hard to crack open.

Your other option is to obtain your DataContext from a factory method, so that you can hide which constructor is actually used. Even better if you do this via an IoC framework like Castle Windsor. Then you'd be able to do things like:

var context = container.Resolve<DataContext>();

Answer 2

This is a bit 'hacky' but you could add a parameter to your constructor (an unused one?), use this constructor everywhere and the default one created by the designer won't cause you any problems.

Kindness,

Dan

Answer 3

While in the designer for the DBML, you can right-click on any white-space, and click on Properties (not the same as right-clicking on the DBML file and clicking Properties). From there, expand the "Connection" option. Set "Application Settings" to False and clear out the "Connection String" setting. These settings are what the designer uses to create that default constructor.

From there, you can add use the default constructor you've created outside of the designer.cs file. Unfortunately, you'll have to repeat this process everything you add any new tables to the designer. It's annoying, and I feel your pain.