2010 SPWebConfigModifications Applied

I have been noticing a few issues about SPWebConfigModifications and how they are applied.

Service Level SPWebConfigModification Applied

For instance if you have two web applications on your content service one on port 80 and other on port 8080. You can choose to have your web config modifications added to all of web applications by adding them at the SPWebService level.

SPWebService.ContentService.WebConfigModificaitons.Add(myWebConfigModification);
SPWebService.ContentService.Update();
SPWebService.ContentService.ApplyWebConfigModifications();

Advantages:

• Applied to all web applications at once
• Applied to new web applications when created
• Can be used in an auto activated farm SPFeatureDefinition

Disadvantages

• Will be applied to web applications set up by third party applications that may have special purposes which may damage these applications
• The actual SPWebModificaitons may reference specific solution based software that may not be deployed globally

Web Application Level SPWebConfigModificaitons

Alternatively it is possible to apply SPWebConfigModificaiton to a specific SPWebApplicaiton.

SPWebApplication myWebApplication;
:
myWebApplication.WebConfigModifications.Add(myWebConfigModification);
myWebApplication.Update();
SPWebService.ContentService.ApplyWebConfigModifications();

Advantages:

• Scopes to the WebApplication level SPFeatureDefinition
• Can be added to a WebApplication deployed SPSolution
• Can be added to a WebApplicaition feature that may be auto activated/deactivated

Disadvantages:

• Auto activate features always activate on create new web application.  You must make sure all necessary infrastructure pieces are in place to support the new web application as it bootstraps into IIS.

Summary:

In general the create new web application use case is often the most overlooked use case by developers.  SPWebService level SPWebConfigModificaitons will be applied to this use case.  Additionally WebApplication auto activate features will be applied to this use case.  As you program SPWebConfigModificaitons, make sure you do not block the farm administrator from creating new web applications.

Programmatically Activating Features just after Deployment

There are a variety of scenarios where features need to be programmatically activated just after a solution has been deployed.  I have found that even when the SPSolution object says it has been deployed, it really isn’t finished deploying.  Sometimes my SPFeatureDefinitions are either non existents or not installed even when the deployment is “done”.  They eventually do show up. Until they do, feature activation fails when the feature is added to the SPFeatureCollection of the SPFarm, SPWebApplication, SPSite, or SPWeb.  I ended up coding a small bit of code to work around this problem.  This example shows activation of a web application scope feature, but the algorithm can be applied to a feature of any scope.

private void ActivateWebApplicationFeature(Uri webApplicaitonUri, Guid featureId, int timeoutSeconds)
{
    const int sleepTime = 1000;
    for (int i = 0; i < timeoutSeconds; i++)
    {
        try
        {
            SPFeatureDefinition definition = SPFarm.Local.FeatureDefinitions[featureId];
            if (definition.Status == SPObjectStatus.Online)
            {
                break;
            }
            Thread.Sleep(sleepTime);
        }
        catch
        {
            Thread.Sleep(sleepTime);
        }
    }
    SPWebApplication application = SPWebApplication.Lookup(webApplicaitonUri);
    if (application.Features[featureId] == null)
    {
        AddWebApplicationFeature(webApplicaitonUri, featureId);
    }
}

private void AddWebApplicationFeature(string webApplicaitonUri, Guid featureId)
{
    int count = 0;
    while (true)
    {
        try
        {
            SPWebApplication application = SPWebApplication.Lookup(webApplicaitonUri);
            application.Features.Add(featureId);
            application.Update();
            break;
        }
        catch (SPDeletedConcurrencyException)
        {
            // Done. This object is gone so we are finished.
            // Optional logging of condition
            break;
        }
        catch (SPUpdatedConcurrencyException)
        {
            count++;
            if (count > 10)
            {
                throw;
            }
        }
    }
}

The algorithm is to first wait for the feature definition to appear.   When looking up the SPFeatureDefinition in the SPFeatureDefinitionCollection an exception will be thrown until the definition has been added.  The code waits a second between checks.  It continues waiting for the SPFeatureDefinition to install.  Finally it activates the feature if the feature needs activation (in certain upgrade scenarios the feature may already be active).  You will notice that the second method uses my technique to control SPDeletedConcurrencyException and SPUpdatedConcurrencyException.