Custom rule property function. Based on https://dovetailsoftware.github.io/property-extensions/

NumberOfOpenChildCasesOnParent.cs

using System.Linq;
using Dovetail.SDK.Clarify;
using Dovetail.SDK.Properties;
using Dovetail.SDK.Properties.Functions;
using FubuCore;

namespace Dovetail.PropertyExtensionExamples.Functions
{
    // NumberOfOpenChildCasesOnParent
    public class NumberOfOpenChildCasesOnParent : IPropertyFunction
	{
		public static int ClosedStatus = 4;
		public static int ClosedAdminPendingStatus = 68;

		public string Execute(TemplateContext context, IServiceLocator services)
		{
			var session = services.GetInstance<IClarifySession>();
			var ds = session.CreateDataSet();
            var parentCaseObjId = 0;

            var childCaseGeneric = ds.CreateGenericWithFields("case", "case_victim2case");
            childCaseGeneric.Filter(_ => _.Equals("objid", (int)context.ObjectId));
            childCaseGeneric.Query();

            if (childCaseGeneric.Count == 1)
                parentCaseObjId = childCaseGeneric.Rows[0].AsInt("case_victim2case");

            var generic = ds.CreateGenericWithFields("victimcase");
			generic.Filter(_ => _.Equals("supercase_objid", (int)parentCaseObjId));
			generic.Filter(_ => _.IsNotIn("clarify_state", ClosedStatus, ClosedAdminPendingStatus));

			generic.Query();

			return generic.DataRows().Count().ToString();
		}
	}
	// ENDSAMPLE
}