Rock.Model.PageService.GetByParentPageId C# (CSharp) Method

        public IOrderedQueryable<Page> GetByParentPageId( int? parentPageId, string includes = null )
        {
            return Queryable( includes ).Where( t => ( t.ParentPageId == parentPageId || ( parentPageId == null && t.ParentPageId == null ) ) ).OrderBy( t => t.Order );
        }

        /// <summary>
        /// Handles the Click event of the btnSave control.
        /// </summary>
        /// <param name="sender">The source of the event.</param>
        /// <param name="e">The <see cref="EventArgs" /> instance containing the event data.</param>
        protected void btnSave_Click( object sender, EventArgs e )
        {
            Site site;

            if ( Page.IsValid )
            {
                var rockContext = new RockContext();
                SiteService siteService = new SiteService( rockContext );
                SiteDomainService siteDomainService = new SiteDomainService( rockContext );
                bool newSite = false;

                int siteId = int.Parse( hfSiteId.Value );

                if ( siteId == 0 )
                {
                    newSite = true;
                    site = new Rock.Model.Site();
                    siteService.Add( site );
                }
                else
                {
                    site = siteService.Get( siteId );
                }

                site.Name = tbSiteName.Text;
                site.Description = tbDescription.Text;
                site.Theme = ddlTheme.Text;
                site.DefaultPageId = ppDefaultPage.PageId;
                site.DefaultPageRouteId = ppDefaultPage.PageRouteId;
                site.LoginPageId = ppLoginPage.PageId;
                site.LoginPageRouteId = ppLoginPage.PageRouteId;
                site.CommunicationPageId = ppCommunicationPage.PageId;
                site.CommunicationPageRouteId = ppCommunicationPage.PageRouteId;
                site.RegistrationPageId = ppRegistrationPage.PageId;
                site.RegistrationPageRouteId = ppRegistrationPage.PageRouteId;
                site.PageNotFoundPageId = ppPageNotFoundPage.PageId;
                site.PageNotFoundPageRouteId = ppPageNotFoundPage.PageRouteId;
                site.ErrorPage = tbErrorPage.Text;
                site.GoogleAnalyticsCode = tbGoogleAnalytics.Text;
                site.FacebookAppId = tbFacebookAppId.Text;
                site.FacebookAppSecret = tbFacebookAppSecret.Text;

                var currentDomains = tbSiteDomains.Text.SplitDelimitedValues().ToList<string>();
                site.SiteDomains = site.SiteDomains ?? new List<SiteDomain>();

                // Remove any deleted domains
                foreach ( var domain in site.SiteDomains.Where( w => !currentDomains.Contains( w.Domain ) ).ToList() )
                {
                    site.SiteDomains.Remove( domain );
                    siteDomainService.Delete( domain );
                }

                foreach ( string domain in currentDomains )
                {
                    SiteDomain sd = site.SiteDomains.Where( d => d.Domain == domain ).FirstOrDefault();
                    if ( sd == null )
                    {
                        sd = new SiteDomain();
                        sd.Domain = domain;
                        sd.Guid = Guid.NewGuid();
                        site.SiteDomains.Add( sd );
                    }
                }

                if ( !site.DefaultPageId.HasValue && !newSite )
                {
                    ppDefaultPage.ShowErrorMessage( "Default Page is required." );
                    return;
                }

                if ( !site.IsValid )
                {
                    // Controls will render the error messages
                    return;
                }

                rockContext.WrapTransaction( () =>
                {
                    rockContext.SaveChanges();

                    if ( newSite )
                    {
                        Rock.Security.Authorization.CopyAuthorization( RockPage.Layout.Site, site, rockContext );
                    }
                } );

                SiteCache.Flush( site.Id );

                // Create the default page is this is a new site
                if ( !site.DefaultPageId.HasValue && newSite )
                {
                    var siteCache = SiteCache.Read( site.Id );

                    // Create the layouts for the site, and find the first one
                    LayoutService.RegisterLayouts( Request.MapPath( "~" ), siteCache );

                    var layoutService = new LayoutService( rockContext );
                    var layouts = layoutService.GetBySiteId( siteCache.Id );
                    Layout layout = layouts.FirstOrDefault( l => l.FileName.Equals( "FullWidth", StringComparison.OrdinalIgnoreCase ) );
                    if ( layout == null )
                    {
                        layout = layouts.FirstOrDefault();
                    }
                    if ( layout != null )
                    {
                        var pageService = new PageService( rockContext );
                        var page = new Page();
                        page.LayoutId = layout.Id;
                        page.PageTitle = siteCache.Name + " Home Page";
                        page.InternalName = page.PageTitle;
                        page.BrowserTitle = page.PageTitle;
                        page.EnableViewState = true;
                        page.IncludeAdminFooter = true;
                        page.MenuDisplayChildPages = true;

                        var lastPage = pageService.GetByParentPageId( null ).
                            OrderByDescending( b => b.Order ).FirstOrDefault();

                        page.Order = lastPage != null ? lastPage.Order + 1 : 0;
                        pageService.Add( page );

                        rockContext.SaveChanges();

                        site = siteService.Get( siteCache.Id );
                        site.DefaultPageId = page.Id;

                        rockContext.SaveChanges();

                        SiteCache.Flush( site.Id );
                    }
                }

                var qryParams = new Dictionary<string, string>();
                qryParams["siteId"] = site.Id.ToString();

                NavigateToPage( RockPage.Guid, qryParams );
            }
        }