# Pastebin XhDlFzqH

namespace API.Services
{
    public class EntityDataTableService<TEntity> : IEntityDataTableService<TEntity> where TEntity : EntityBase, new()
    {
        private readonly ILogger<TEntity> _logger;
        private readonly IMapper _mapper;
        private WuitCMDBDbContext _context;
        string errorMessage = string.Empty;

        public EntityDataTableService(
            WuitCMDBDbContext context,
            ILogger<TEntity> logger,
            IMapper mapper)
        {
            this._context = context;
            _logger = logger;
            _mapper = mapper;
        }

        public DataTableResponseJsonModel<TViewModel> JQueryDataTable<TViewModel>(
            DataTablesAjaxPostViewModel dataTableRequest,
            Expression<Func<TViewModel, bool>> customFilterPredicate = null)
        {
            // if columns[i].search is populated, but stringProperties is null, we are just going to ignore the search.
            // Maybe we should throw a warning so the developer can be made aware that searches are taking place but are not configured?

            if (dataTableRequest == null)
            {
                throw new ArgumentNullException(nameof(dataTableRequest));
            }

            if (dataTableRequest.order == null || dataTableRequest.order.Count <= 0)
            {
                throw new ArgumentNullException(nameof(dataTableRequest.order));
            }

            IQueryable<TEntity> query = _context.Set<TEntity>();

            var projectedQuery = query
                .AsNoTracking()
                .ProjectTo<TViewModel>();

            //
            // Global filtering
            //
            if(customFilterPredicate != null)
            {
                projectedQuery = projectedQuery.Where(customFilterPredicate);
            }

            //
            // Column Searching
            //
            if (stringProperties != null)
            {
                foreach (var column in dataTableRequest.columns.Where(x => x.searchable && !string.IsNullOrWhiteSpace(x.search.value)))
                {
                    projectedQuery = projectedQuery
                        .Search( ... ) // PROBLEM. All I have is `dataTableRequest.columns[i].name`, I also only have TViewModel, so I am unable to configure the properties of TViewModel I want to search against.
                        // Should I move this up and out so the caller (controller action) can configure it knowing the real type? Is there some magic reflection I can use here?
                        .Containing(column.search.value);
                }
            }

            //
            // Ordering
            //
            foreach (var orderRequest in dataTableRequest.order)
            {
                var orderColumn = dataTableRequest.columns[orderRequest.column];
                if (orderColumn.orderable)
                {
                    var orderColumnsName = !string.IsNullOrWhiteSpace(orderColumn.name) ? orderColumn.name : orderColumn.data;
                    projectedQuery = projectedQuery.OrderBy($"{orderColumnsName} {orderRequest.dir}");
                }
            }

            //
            // Paging
            //
            var responseViewModel =
                projectedQuery
                .ToPagedList(dataTableRequest.StartPage, dataTableRequest.length) // Query Execution
                .ToResponseViewModel(query.Count(), dataTableRequest.draw); // Query Execution

            return responseViewModel;
        }
    }
}