return System.Linq.Queryable
                // ReSharper disable once InvokeAsExtensionMethod
                .Union(
                    ProjectProduct.All
                        .OfType<ProjectCable>()
                        .Where(pc => pc.SignalProtocol == this)
                        .OfType<ProjectProduct>(),
                    ProjectProduct.All
                        .OfType<ProjectConnector>()
                        .Where(pc => pc.Io.Protocol == this)
                        .OfType<ProjectProduct>())
                .Join(ProjectProductDrawing.All,
                    pp => pp,
                    ppd => ppd.ProjectProduct,
                    (pp, ppd) => ppd.Drawing)
                .Distinct();