public IEnumerable <ValidationResult> Validate(ValidationContext validationContext) { var errors = new List <ValidationResult>(); if (TechnicalAssistanceRequestSimples != null) { var reportedYears = TechnicalAssistanceRequestSimples.Select(x => x.FiscalYear).Distinct().OrderByDescending(x => x).ToList(); var reportedYearsMissingData = reportedYears?.Select(x => x).Where(x => TechnicalAssistanceRequestSimples.Any(y => y.FiscalYear == x && y.TechnicalAssistanceTypeID == null)).ToList(); reportedYearsMissingData?.ForEach(x => errors.Add(new ValidationResult($"{x} has rows missing a value for Assistance Type."))); } return(errors); }