What field attribute will allow me to calculate if a Case exists with certain criteria?

I would like to add a custom field to a Business Account which will automatically calculate if a Case exists for the Business Account in question with a Case Class matching one of a few, and with a Subject starting with ‘2021’.

I have this so far, which does not work:

[PXDBScalar(typeof(Switch<Case<Where<SearchFor<CRCase.caseCD>.
  In<SelectFrom<CRCase>.
    LeftJoin<BAccount>.
      On<CRCase.customerID.IsEqual<BAccount.bAccountID>>.
    Where<BAccount.bAccountID.IsEqual<BAccount.bAccountID.FromCurrent>.
      And<CRCase.subject.StartsWith<CstConstant.year>>.
      And<Brackets<CRCase.caseClassID.IsEqual<CstConstant.txReturnType_CTR>.
        Or<CRCase.caseClassID.IsEqual<CstConstant.txReturnType_FTR>>.
          Or<CRCase.caseClassID.IsEqual<CstConstant.txReturnType_ITR>>.
            Or<CRCase.caseClassID.IsEqual<CstConstant.txReturnType_PTR>>.
              Or<CRCase.caseClassID.IsEqual<CstConstant.txReturnType_SCTR>>.
                Or<CRCase.caseClassID.IsEqual<CstConstant.txReturnType_SMLLC>>>>>>, IsNotNull>, True>, False>))]