Server-side grid virtualization: DxGrid adapter & API

Implemented MgGridVirtualizedDataSource<T> for DevExpress DxGrid integration, enabling server-side paging/filtering/sorting via SignalR. Added developer-only test page and menu entry. Extended IFruitBankDataControllerCommon and client DTOs for virtualized queries. Renamed ToPagedListAsync to ToGridListAsync and improved AcGridCriteriaTranslator to whitelist only real DB columns. Temporarily relaxed relation-path filtering/sorting for closed testing (see ACCORE-SIGVDS-T-R7X2). Updated documentation, TODOs, icons, CSS, and local dev tooling. Feature is developer-only and not enabled in production grids.

AyCode.Blazor.Components/Components/Grids/MgGridVirtualizedDataSource.cs

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+using System.Collections;
+using AyCode.Core.Interfaces;
+using AyCode.Services.SignalRs;
+using DevExpress.Blazor;
+using DevExpress.Data.Filtering;
+using DevExpress.Data.Filtering.Helpers;   // ReferenceEqualsNull extension
+
+namespace AyCode.Blazor.Components.Components.Grids;
+
+/// <summary>
+/// DevExpress-facing adapter for <see cref="GridDataMode.ServerVirtualized"/>: translates DxGrid load options
+/// into <see cref="AcSignalRVirtualizedDataSource{TDataItem, TId}"/> calls. Composition, not inheritance — the
+/// datasource keeps its own base.
+/// </summary>
+/// <remarks>Contract: <c>AyCode.Services/docs/SIGNALR_VIRTUALIZED_DATASOURCE/README.md</c> (AyCode.Core repo).</remarks>
+public class MgGridVirtualizedDataSource<TDataItem, TId> : GridCustomDataSource
+    where TDataItem : class, IId<TId> where TId : struct
+{
+    private readonly AcSignalRVirtualizedDataSource<TDataItem, TId> _dataSource;
+
+    public MgGridVirtualizedDataSource(AcSignalRVirtualizedDataSource<TDataItem, TId> dataSource)
+        => _dataSource = dataSource ?? throw new ArgumentNullException(nameof(dataSource));
+
+    protected override Type DataItemType => typeof(TDataItem);
+
+    /// <summary>The wrapped datasource — for save operations and scope changes (<c>CustomFilterCriteria</c>).</summary>
+    public AcSignalRVirtualizedDataSource<TDataItem, TId> DataSource => _dataSource;
+
+    public override async Task<IList> GetItemsAsync(GridCustomDataSourceItemsOptions options, CancellationToken cancellationToken)
+    {
+        var result = await _dataSource.LoadPageAsync(
+            ToCriteriaString(options.FilterCriteria), ToSortDescriptors(options.SortInfo),
+            options.StartIndex, ToTake(options.Count));
+
+        // Server order IS display order: under a custom data source the grid does not re-sort.
+        return result.Items!;
+    }
+
+    /// <summary>
+    /// Count-only probe (<c>Take = 0</c>): the server computes the total and returns an EMPTY page, so this
+    /// costs a round trip but no rows. Deliberately naive for the first version — correct regardless of the
+    /// order in which DevExpress calls the two methods. Caching the total from the last page response (keyed by
+    /// filter, since paging does not change it) is the obvious optimization once the real call pattern is
+    /// measured.
+    /// </summary>
+    public override async Task<int> GetItemCountAsync(GridCustomDataSourceCountOptions options, CancellationToken cancellationToken)
+    {
+        var result = await _dataSource.LoadPageAsync(
+            ToCriteriaString(options.FilterCriteria), sort: null, skip: null, take: 0);
+
+        return result.TotalRecords!.Value;
+    }
+
+    #region Option translation
+
+    /// <summary>
+    /// <c>CriteriaOperator</c> overloads <c>==</c>, so <c>criteria == null</c> does NOT do what it looks like —
+    /// <c>ReferenceEqualsNull()</c> is the correct test.
+    /// </summary>
+    private static string? ToCriteriaString(CriteriaOperator criteria)
+        => criteria.ReferenceEqualsNull() ? null : CriteriaOperator.ToString(criteria);
+
+    /// <summary>
+    /// A NEGATIVE <c>Count</c> means "no paging, return everything" — passing it through would emit
+    /// <c>Take(-1)</c>. Maps to <c>null</c> (no page size).
+    /// </summary>
+    private static int? ToTake(int count) => count >= 0 ? count : null;
+
+    private static List<AcGridSortDescriptor>? ToSortDescriptors(IReadOnlyList<GridCustomDataSourceSortInfo>? sortInfo)
+    {
+        if (sortInfo is not { Count: > 0 })
+            return null;
+
+        var result = new List<AcGridSortDescriptor>(sortInfo.Count);
+        foreach (var info in sortInfo)
+            result.Add(new AcGridSortDescriptor { FieldName = info.FieldName, Descending = info.DescendingSortOrder });
+
+        return result;
+    }
+
+    #endregion
+}