Some function

public async Task<List<ProductCombinationsModel>> GetProductAvailableCategoryAttributeCombinations(SearchAttributesModel searchModel)
        {
            List<ProductAttributeDetail> productAttributeDetails = new List<ProductAttributeDetail>();

            //if (searchModel.SelectedCategoryAttributeValueIds != null)
            //{
            //    productAttributeDetails = _productAttributeDetailRepository
            //        .Table.Where(x => x.ProductAttribute.ProductId == searchModel.ProductId && searchModel.SelectedCategoryAttributeValueIds.Contains(x.CategoryAttributeValueId)).SelectMany(x => x.ProductAttribute.ProductAttributeDetail).ToList();

            //    productAttributeDetails = _productAttributeRepository
            //        .Table.Where(x => x.ProductId == searchModel.ProductId && x.ProductAttributeDetail.Count(pad => searchModel.SelectedCategoryAttributeValueIds.Contains(pad.CategoryAttributeValueId)) >= searchModel.SelectedCategoryAttributeValueIds.Count - 1).SelectMany(x => x.ProductAttributeDetail).ToList();
            //}
            //else
            //{
                productAttributeDetails = _productAttributeDetailRepository
                    .Table.Where(x => x.ProductAttribute.ProductId == searchModel.ProductId).SelectMany(x => x.ProductAttribute.ProductAttributeDetail).ToList();
            //}


            var groupedResult = productAttributeDetails.GroupBy(x => x.CategoryAttributeId);

            var list = groupedResult.ToList();


            List<ProductCombinationsModel> data = new List<ProductCombinationsModel>();
            foreach(var result in groupedResult)
            {
                ProductCombinationsModel model = new ProductCombinationsModel();

                model.ProductId = searchModel.ProductId;
                model.CategoryAttributeId = result.Key;
                model.CategoryAttributeName = _categoryAttributeRepository.GetNameById(model.CategoryAttributeId);

                var valueIds = result.Select(x => x.CategoryAttributeValueId).Distinct();
                var otherValues = searchModel.SelectedCategoryAttributeValueIds != null
                    ? searchModel.SelectedCategoryAttributeValueIds.Where(x => !valueIds.Contains(x))
                    : null;

                if (searchModel.SelectedCategoryAttributeValueIds != null && otherValues != null)
                {
                    model.CategoryAttributeValues = _productAttributeDetailRepository.Table.Where(x => x.CategoryAttributeId == model.CategoryAttributeId && x.ProductAttribute.ProductId == searchModel.ProductId && x.ProductAttribute.ProductAttributeDetail.Count(pad => otherValues.Contains(pad.CategoryAttributeValueId)) == otherValues.Count())
                        .Select(x => x.CategoryAttributeValue).Distinct().ProjectTo<CategoryAttributeValueViewModel>().ToList();

                    foreach (var attributeValue in model.CategoryAttributeValues)
                    {
                        if (searchModel.SelectedCategoryAttributeValueIds.Contains(attributeValue.Id.Value))
                        {
                            attributeValue.Selected = true;
                        }
                    }
                }
                else
                {
                    model.CategoryAttributeValues = _categoryAttributeValueRepository.Table.Where(x => valueIds.Contains(x.Id)).ProjectTo<CategoryAttributeValueViewModel>().ToList();
                }

                data.Add(model);
            }

            foreach(var model in data)
            {
                var categoryId = model.CategoryAttributeId;
                var categoryValueId = model.CategoryAttributeValues.FirstOrDefault(x => x.Selected);

                if (categoryValueId == null) break;

                var productAttributeId = _productAttributeDetailRepository.GetMany(x => x.CategoryAttributeId == categoryId && x.CategoryAttributeValueId == categoryValueId.Id).Select(x => x.ProductAttributeId).ToList();
                foreach (var id in productAttributeId)
                {
                    var productAtttibute = _productAttributeRepository.Get(x => x.Id == id);
                    if (productAtttibute.ProductId == searchModel.ProductId)
                    {
                        var quantity = productAtttibute.Quantity;
                        var items = await _orderItemRepository.CountAsync(x => x.ProductAttributeId == id && x.RentalStartDateUtc <= searchModel.ToDate && x.ProductId == searchModel.ProductId || x.ProductAttributeId == id && x.RentalEndDateUtc >= searchModel.FromDate && x.ProductId == searchModel.ProductId);

                        if (quantity - items == 0)
                        {
                            var detail = productAtttibute.ProductAttributeDetail;
                            if (detail.Count == 1)
                            {
                                var deleteModel = model.CategoryAttributeValues.First(x => x.Id == detail.FirstOrDefault().CategoryAttributeValueId);
                                Debug.WriteLine(id);
                                foreach (var tt in data)
                                {
                                    tt.CategoryAttributeValues.Remove(deleteModel);
                                }
                            }
                        }
                    }
                }
            }

            return data;
        }