Problem:

When we turned off the soft delete filter on our Entity Framework DB connection, we got SQL Exception 26: Error Locating Server/Instance Specified. At first we thought it was a SQL Server configuration configuration or permissions issue, but we were able to isolate it to the soft delete filter.

Diagnosis:

The way we set up our Soft Delete Interceptor using the EntityFramework.DynamicFilters library, the soft delete filter was turned on in a base class that extended DbContext. It was set up like this:

class ApplicationDb : SoftDeleteDb 
{
	ApplicationDb(string connectionString, bool softDeleteFilterActive) : base(softDeleteFilterActive)
	{
		Database.Connection.ConnectionString = connectionString;
	
		Database.SetInitializer<ApplicationDb>(null);
	}
}

class SoftDeleteDb : DbContext 
{
	SoftDeleteDb(bool softDeleteFilterActive) 
	{
		if (!softDeleteFilterActive) 
		{
			// extension method for DbContext provided by EntityFramework.DynamicFilters library
            this.DisableFilter(SOFT_DELETE_FILTER_NAME);
		}
	}
}

Looking at the source of the extension method we call, it turns out it needs to use the DbContext's Database.Connection.ConnectionString. So, setting the connection string needed to be moved to the SoftDeleteDb constructor.

The connection string info must be passed as a parameter and set in the SoftDeleteDb constructor, because in C# the base class's constructor must always be called first if the subclass overrides a constructor. That is, the code below doesn't work:

class Subclass : BaseClass 
{
	Subclass(bool param) 
	{
		MyBaseClassProperty = param;
		// line below does not compile
		base();
	}	
}

Solution

Set the DbContext.Database.Connection.ConnectionString before calling DbContext.DisableFilter.

class ApplicationDb : SoftDeleteDb 
{
	ApplicationDb(string connectionString, bool softDeleteFilterActive) : base(connectionString, softDeleteFilterActive)
	{	
		Database.SetInitializer<ApplicationDb>(null);
	}
}

class SoftDeleteDb : DbContext 
{
	SoftDeleteDb(string connectionString, bool softDeleteFilterActive) 
	{
		Database.Connection.ConnectionString = connectionString;

		if (!softDeleteFilterActive) 
		{
			// extension method for DbContext provided by EntityFramework.DynamicFilters library
            this.DisableFilter(SOFT_DELETE_FILTER_NAME);
		}
	}
}