LINQ to SQL generator fails due to custom code

Today I decided to do something quite innocuous, or so I thought, on an existing application that happened to use LINQ to SQL. I needed to add an additional field to an existing table which I did quite easily via SSMS. However, when I came to update the LINQ to SQL model file I ran into all sorts of issues. The easiest way I’ve found in the past to update the LINQ to SQL model is to simply delete the table that you need to update and drag it onto the design surface from Server Explorer. Normally this updates the model and doesn’t usually break anything (unless you say delete a field that is in use in your code in which case the compile error is an artefact you want).

Today this process seemed to go completely haywire for no reason. I was getting 10-15 compile errors – since I was just adding a field I shouldn’t have seen any. Thinking that I’d broken something accidentally I reverted back to the version in subversion and tried again. Same result. Looking in Solution Explorer it was clear why these errors were being generated – there was no .designer.cs file to go alongside the .dbml LINQ to SQL model file.

I right-click on the dbml file in Solution Explorer and selected “Run Custom Tool” (for those unfamiliar with the Visual Studio custom tool model this is essentially an external executable that is called to automatically create or modify files in your solution – in this case create the .designer.cs file). This time I at least got an error message:


Error: The custom tool ‘MSLinqToSQLGenerator’ failed. Unsepecifed error

Interestingly it also opened up a file in which I had added some custom properties for my LINQ to SQL entities. I found that if I excluded this file from my solution I was again able to run the custom tool to generate the .designer.cs file. So, in order to make schema changes from now on I need to:

-Exclude my custom properties file

-Make changes to my LINQ to SQL model

-Run the Custom tool to generate the .designer.cs file – this is automatically run if you save or close the model designer

Update: Actually, you need to do a build of the project that contains the LINQ to SQL model prior to adding the custom properties file back into the project. Otherwise Visual Studio decides to nuke the .designer.cs file again.

-Include my custom properties files

-Rebuild my solution.

Hope this helps anyone else seeing the same issue

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