Add Safe control entry in web.coinfig using SPWebConfigModification Class

SPWebConfigModification Class : Holds modifications that are made to the web.config. Following example helps you to add the safe control entry on feature activation.

public override void FeatureActivated(SPFeatureReceiverProperties properties)

        {

            try

            {

                SPWebService contentService = SPWebService.ContentService;

                contentService.WebConfigModifications.Add(GetConfigModification());

                // Serialize the web application state and propagate changes across the farm.

                contentService.Update();

                // Save web.config changes.

                contentService.ApplyWebConfigModifications();

            }

            catch (Exception e)

            {

                Console.WriteLine(e.ToString());

                throw;

            }

        }

        public override void FeatureDeactivating(SPFeatureReceiverProperties properties)

        {

            try

            {

                SPWebService contentService = SPWebService.ContentService;

                contentService.WebConfigModifications.Remove(GetConfigModification());

                // Serialize the web application state and propagate changes across the farm.

                contentService.Update();

                // Save web.config changes.

                contentService.ApplyWebConfigModifications();

            }

            catch (Exception e)

            {

                Console.WriteLine(e.ToString());

                throw;

            }

        }

public SPWebConfigModification GetConfigModification()

        {

            string assemblyValue = typeof(Purchaseclass).Assembly.FullName;

            string namespaceValue = typeof(Purchaseclass).Namespace;

            SPWebConfigModification modification = new SPWebConfigModification(

                string.Format(CultureInfo.CurrentCulture,

                    "SafeControl[@Assembly='{0}'][@Namespace='{1}'][@TypeName='*'][@Safe='True']", assemblyValue, namespaceValue),

                "configuration/SharePoint/SafeControls");

            modification.Owner = "Patterns and Practices";

            modification.Sequence = 0;

            modification.Type = SPWebConfigModification.SPWebConfigModificationType.EnsureChildNode;

            modification.Value =

                string.Format(CultureInfo.CurrentCulture,

                "<SafeControl  Assembly=\"{0}\" Namespace=\"{1}\" TypeName=\"*\" Safe=\"True\" />", assemblyValue, namespaceValue);

            return modification;

        }