Datatables implementation, backend only.

GetTrackerPaginatedList.cs

/// <summary>
/// Retrieves a paginated list of trackers for a given request, supporting sorting, searching, and pagination.
/// Returns an object tailored for listing, <see cref="ListedTrackerDto"/>.
/// This method may be used with frontend calls compatible with DataTables.
/// </summary>
/// <param name="requestId">The ID of the specific request for which trackers are being retrieved.</param>
/// <returns>A JSON object containing paginated tracker data, total records, and any error messages if an exception occurs.</returns>
[HttpPost]
public virtual ActionResult GetTrackerPaginatedList(int requestId)
{
    // Retrieve the current user ID from the account service to ensure access is scoped to this user
    int userId = _accountService.UserID;

    try
    {

        // DataTables Parameters: fetch values from the form data, using safe fallback values
        string draw = Request.Form["draw"] ?? string.Empty; // Unique identifier for the DataTables request
        string start = Request.Form["start"] ?? "0"; // Starting index of records (pagination)
        string length = Request.Form["length"] ?? "10"; // Number of records to return (page size)
        string sortColumn = Request.Form[$"columns[{Request.Form["order[0][column]"]}][name]"] ?? string.Empty; // Column to sort by
        string sortColumnDirection = Request.Form["order[0][dir]"] ?? "asc"; // Sort direction (asc or desc)
        string searchedValue = Request.Form["search[value]"] ?? string.Empty; // Search query entered by the user

        // Parse pagination parameters safely
        int pageSize = int.TryParse(length, out int len) ? len : 10;
        int skip = int.TryParse(start, out int st) ? st : 0;

        // Fetch the list of trackers with IQueryable for deferred execution
        IQueryable<ListedTrackerDto> listedTrackers = _trackerService.GetListedTrackerQueryable(userId, requestId);

        // Apply search filter: match trackers by various properties if a search value is provided
        if (!string.IsNullOrEmpty(searchedValue))
        {
            listedTrackers = listedTrackers.Where(m => m.TrackerCode.Contains(searchedValue)
                                                        || m.MineralName.Contains(searchedValue)
                                                        || m.ExpeditionDate.Contains(searchedValue)
                                                        || m.ExpeditionTime.Contains(searchedValue)
                                                        || m.MineralQuantity.Contains(searchedValue));
        }

        // Count the total records after filtering, for pagination
        int recordsTotal = listedTrackers.Count();

        // Apply sorting dynamically if a valid column and direction are provided
        if (!string.IsNullOrEmpty(sortColumn) && !string.IsNullOrEmpty(sortColumnDirection))
        {
            // Dynamically build an order expression using LINQ's dynamic sorting syntax
            listedTrackers = listedTrackers.OrderBy($"{sortColumn} {sortColumnDirection}");
        }

        // Handle pagination: retrieve a subset based on page size if provided
        List<ListedTrackerDto> listedTrackersJson = pageSize < 0
            ? listedTrackers.ToList() // No pagination, return all records
            : listedTrackers.Skip(skip).Take(pageSize).ToList(); // Skip and take for paginated results

        // Return JSON response in a DataTables-compatible format
        return Json(new { draw, recordsFiltered = recordsTotal, recordsTotal, data = listedTrackersJson });
    }
    catch (Exception ex)
    {
        // Log the error with additional context, capturing user ID and request ID for debugging
        string errorId = LogHelper.LogError(ex, "Tracker", "GetTrackerPaginatedList");
        //string errorId = LogHelper.LogError(ex, "Tracker", "GetTrackerPaginatedList", $"UserId: {userId}, RequestId: {requestId}");

        // Return a JSON response with a user-friendly error message and type
        return Json(new
        {
            type = Config.ReturnViewType.Alert, // Return an alert to inform the user of the error
            data = string.Format(Resources.Global.TRY_CATCH_ERROR_MESSAGE, errorId) // Display a general error message with log reference
        });
    }
}