fix(board): commit a search only after its query succeeds and report read failures

A failed read on a UI path (sort change, clear, refresh after a write, opening a
card, the tag picker, the tags tab) used to escape as an unhandled exception.
Reads now run before the view is cleared and report Error_Read_* instead; the
active filter changes only once its query has run. DataWritten and TagsChanged
fire only after a successful refresh, so a broken database shows one dialog.

YKanBan.Tests/ViewModels/BoardViewModelTests.cs

@@ -285,6 +285,52 @@ public class BoardViewModelTests
         Assert.AreEqual(0, fixture.Repository.GetCards().Count);
     }
 
+    [TestMethod]
+    public async Task FailedSearchQueryIsReportedAndKeepsThePreviousResultAndFilter()
+    {
+        using var fixture = new Fixture();
+        ColumnModel column = fixture.Repository.AddColumn("A", "");
+        fixture.Repository.AddCard(column.Id, "alpha", "", []);
+        fixture.Repository.AddCard(column.Id, "beta", "", []);
+        BoardViewModel board = fixture.CreateBoard();
+        board.SearchText = "alpha";
+        await board.SearchCommand.ExecuteAsync(null);
+        CompiledSearch? alphaFilter = board.ActiveFilter;
+
+        // Every read fails from now on.
+        fixture.Repository.Dispose();
+        board.SearchText = "beta";
+        await board.SearchCommand.ExecuteAsync(null);
+
+        var error = (MessageDialogViewModel)fixture.Dialogs.Shown.Single();
+        Assert.AreEqual(Resources.Error_Read_Title, error.Title);
+        Assert.AreSame(alphaFilter, board.ActiveFilter);
+        CollectionAssert.AreEqual(new[] { "alpha" }, board.Columns.Single().Cards.Select(card => card.Title).ToArray());
+    }
+
+    [TestMethod]
+    public async Task ReadFailuresOnBoardCommandsAreReportedInsteadOfThrown()
+    {
+        using var fixture = new Fixture();
+        ColumnModel column = fixture.Repository.AddColumn("A", "");
+        CardModel card = fixture.Repository.AddCard(column.Id, "a", "", []);
+        BoardViewModel board = fixture.CreateBoard();
+        var editor = CardEditorDialogViewModel.ForExistingCard(fixture.Repository, fixture.Dialogs, card, confirmDiscard: false);
+        fixture.Repository.Dispose();
+
+        board.SelectedSort = board.SortOptions.Single(option => (CardSortOption)option.Value == CardSortOption.Title);
+        await board.ClearSearchCommand.ExecuteAsync(null);
+        await board.Columns.Single().Cards.Single().EditCommand.ExecuteAsync(null);
+        await board.Columns.Single().Cards.Single().MoveToCommand.ExecuteAsync(column.Id);
+        await editor.AddTagCommand.ExecuteAsync(null);
+
+        // Sort, clear, edit, the failed move with its refresh, and the tag picker.
+        string read = Resources.Error_Read_Title;
+        CollectionAssert.AreEqual(
+            new[] { read, read, read, Resources.Error_Operation_Title, read, read },
+            fixture.Dialogs.Shown.Select(dialog => ((MessageDialogViewModel)dialog).Title).ToArray());
+    }
+
     [TestMethod]
     public void TagPickerReportsInvalidColorAndDuplicateNameWithoutClosing()
     {

YKanBan.Tests/ViewModels/TagsAndSearchViewModelTests.cs

@@ -138,7 +138,7 @@ public class TagsAndSearchViewModelTests
         board.SearchText = "alpha";
         await board.SearchCommand.ExecuteAsync(null);
         Assert.IsTrue(board.HasSearchText);
-        board.ClearSearchCommand.Execute(null);
+        await board.ClearSearchCommand.ExecuteAsync(null);
 
         Assert.AreEqual("", board.SearchText);
         Assert.IsFalse(board.HasSearchText);
@@ -312,6 +312,24 @@ public class TagsAndSearchViewModelTests
         Assert.AreEqual(0, fixture.Repository.GetTags().Count);
     }
 
+    [TestMethod]
+    public async Task TagReadFailuresAreReportedInsteadOfThrown()
+    {
+        using var fixture = new Fixture();
+        fixture.Repository.AddTag("bug", new RgbColor(1, 2, 3), "");
+        fixture.Config.Confirmations.DeleteTag = false;
+        TagsViewModel tags = fixture.CreateTags();
+
+        // Every read and write fails from now on.
+        fixture.Repository.Dispose();
+        await tags.Tags[0].DeleteCommand.ExecuteAsync(null);
+
+        CollectionAssert.AreEqual(
+            new[] { Resources.Error_Operation_Title, Resources.Error_Read_Title },
+            fixture.Dialogs.Shown.Select(dialog => ((MessageDialogViewModel)dialog).Title).ToArray());
+        Assert.AreEqual("bug", tags.Tags.Single().Tag.Name);
+    }
+
     #endregion
 
     #region Workspace wiring and export
@@ -334,7 +352,7 @@ public class TagsAndSearchViewModelTests
         Assert.AreEqual(0, workspace.Board.Columns.Sum(column => column.CardCount));
 
         // Re-tag through the repository, then a board write updates the usage count.
-        workspace.Board.ClearSearchCommand.Execute(null);
+        await workspace.Board.ClearSearchCommand.ExecuteAsync(null);
         TagModel ui = fixture.Repository.AddTag("ui", new RgbColor(4, 5, 6), "");
         fixture.Repository.UpdateCard(card.Id, "a", "", [ui.Id]);
         Assert.AreEqual(0, workspace.Tags.Tags.Count);

YKanBan/Assets/Locales/Resources.resx

@@ -343,6 +343,12 @@
   <data name="Error_Operation_Message" xml:space="preserve">
     <value>The change could not be written to the workspace. The board shows the stored state.</value>
   </data>
+  <data name="Error_Read_Title" xml:space="preserve">
+    <value>Reading failed</value>
+  </data>
+  <data name="Error_Read_Message" xml:space="preserve">
+    <value>The data could not be read from the workspace. What is shown may be out of date.</value>
+  </data>
   <data name="TagEditor_TitleNew" xml:space="preserve">
     <value>New tag</value>
   </data>

YKanBan/Assets/Locales/Resources.zh-Hans.resx

@@ -343,6 +343,12 @@
   <data name="Error_Operation_Message" xml:space="preserve">
     <value>更改未能写入工作区，看板显示的是已保存的状态。</value>
   </data>
+  <data name="Error_Read_Title" xml:space="preserve">
+    <value>读取失败</value>
+  </data>
+  <data name="Error_Read_Message" xml:space="preserve">
+    <value>无法从工作区读取数据，当前显示的内容可能不是最新的。</value>
+  </data>
   <data name="TagEditor_TitleNew" xml:space="preserve">
     <value>新建标签</value>
   </data>

YKanBan/ViewModels/Board/BoardViewModel.cs

@@ -107,10 +107,25 @@ public sealed partial class BoardViewModel : ViewModelBase
     /// <summary>
     /// Reloads the columns and the cards matching <see cref="ActiveFilter"/>.
     /// </summary>
-    public void Refresh()
+    /// <exception cref="Exception">Reading the workspace failed; the board is left unchanged.</exception>
+    public void Refresh() => Load(ActiveFilter);
+
+    /// <summary>
+    /// Reloads like <see cref="Refresh"/>, but reports a read failure in a
+    /// message dialog instead of throwing.
+    /// </summary>
+    /// <returns><see langword="true"/> when the board was reloaded.</returns>
+    public Task<bool> RefreshOrReportAsync() => TryLoadAsync(ActiveFilter);
+
+    /// <summary>
+    /// Reloads the board with the given filter; the columns are only replaced
+    /// once both queries have succeeded.
+    /// </summary>
+    /// <param name="filter">The search to apply; <see langword="null"/> shows every card.</param>
+    private void Load(CompiledSearch? filter)
     {
         IReadOnlyList<ColumnModel> columns = _repository.GetColumns();
-        ILookup<long, CardModel> cardsByColumn = _repository.GetCards(ActiveFilter).ToLookup(card => card.ColumnId);
+        ILookup<long, CardModel> cardsByColumn = _repository.GetCards(filter).ToLookup(card => card.ColumnId);
         var sort = (CardSortOption)SelectedSort.Value;
 
         ColumnModels = columns;
@@ -121,9 +136,30 @@ public sealed partial class BoardViewModel : ViewModelBase
         }
     }
 
+    /// <summary>
+    /// Reloads the board with the given filter and reports a read failure in a message dialog.
+    /// </summary>
+    /// <param name="filter">The search to apply; <see langword="null"/> shows every card.</param>
+    /// <returns><see langword="true"/> when the board was reloaded.</returns>
+    private async Task<bool> TryLoadAsync(CompiledSearch? filter)
+    {
+        try
+        {
+            Load(filter);
+            return true;
+        }
+        catch (Exception exception)
+        {
+            await _dialogs.ShowReadFailedAsync(exception);
+            return false;
+        }
+    }
+
     /// <summary>
     /// Parses and runs the search box text; blank text shows every card. An
-    /// invalid expression only shows the error dialog.
+    /// invalid expression only shows the error dialog. The expression becomes
+    /// <see cref="ActiveFilter"/> only once its query has succeeded, so a failed
+    /// search leaves the previous result and later refreshes untouched.
     /// </summary>
     /// <returns>A task completing after the refresh or the error dialog.</returns>
     [RelayCommand]
@@ -143,19 +179,24 @@ public sealed partial class BoardViewModel : ViewModelBase
             return;
         }
 
-        ActiveFilter = filter;
-        Refresh();
+        if (await TryLoadAsync(filter))
+        {
+            ActiveFilter = filter;
+        }
     }
 
     /// <summary>
     /// Empties the search box and shows every card again.
     /// </summary>
+    /// <returns>A task completing after the refresh.</returns>
     [RelayCommand]
-    private void ClearSearch()
+    private async Task ClearSearchAsync()
     {
         SearchText = "";
-        ActiveFilter = null;
-        Refresh();
+        if (await TryLoadAsync(null))
+        {
+            ActiveFilter = null;
+        }
     }
 
     /// <summary>
@@ -168,7 +209,7 @@ public sealed partial class BoardViewModel : ViewModelBase
         var dialog = new ColumnEditorDialogViewModel(null, (title, description) => _repository.AddColumn(title, description));
         if (await _dialogs.ShowAsync(dialog))
         {
-            RefreshAfterWrite();
+            await RefreshAfterWriteAsync();
         }
     }
 
@@ -196,7 +237,7 @@ public sealed partial class BoardViewModel : ViewModelBase
             column, (title, description) => _repository.UpdateColumn(column.Id, title, description));
         if (await _dialogs.ShowAsync(dialog))
         {
-            RefreshAfterWrite();
+            await RefreshAfterWriteAsync();
         }
     }
 
@@ -235,7 +276,7 @@ public sealed partial class BoardViewModel : ViewModelBase
         await _dialogs.ShowAsync(editor);
 
         // Refresh even after a cancel: the nested picker may have created tags.
-        RefreshAfterWrite();
+        await RefreshAfterWriteAsync();
     }
 
     /// <summary>
@@ -245,17 +286,27 @@ public sealed partial class BoardViewModel : ViewModelBase
     /// <returns>A task completing when the editor closes.</returns>
     internal async Task EditCardAsync(long cardId)
     {
-        CardModel? card = _repository.GetCard(cardId);
+        CardModel? card;
+        try
+        {
+            card = _repository.GetCard(cardId);
+        }
+        catch (Exception exception)
+        {
+            await _dialogs.ShowReadFailedAsync(exception);
+            return;
+        }
+
         if (card is null)
         {
-            Refresh();
+            await RefreshOrReportAsync();
             return;
         }
 
         var editor = CardEditorDialogViewModel.ForExistingCard(
             _repository, _dialogs, card, _config.Confirmations.DiscardEdit);
         await _dialogs.ShowAsync(editor);
-        RefreshAfterWrite();
+        await RefreshAfterWriteAsync();
     }
 
     /// <summary>
@@ -314,16 +365,20 @@ public sealed partial class BoardViewModel : ViewModelBase
             await _dialogs.ShowMessageAsync(
                 Resources.Error_Operation_Title, Resources.Error_Operation_Message, exception.Message);
         }
-        RefreshAfterWrite();
+        await RefreshAfterWriteAsync();
     }
 
     /// <summary>
-    /// Refreshes after a write and announces it.
+    /// Refreshes after a write and announces it; a failed refresh is reported
+    /// and not announced, so a broken workspace yields one read-failure dialog.
     /// </summary>
-    private void RefreshAfterWrite()
+    /// <returns>A task completing after the refresh.</returns>
+    private async Task RefreshAfterWriteAsync()
     {
-        Refresh();
-        DataWritten?.Invoke(this, EventArgs.Empty);
+        if (await RefreshOrReportAsync())
+        {
+            DataWritten?.Invoke(this, EventArgs.Empty);
+        }
     }
 
     /// <summary>
@@ -333,6 +388,8 @@ public sealed partial class BoardViewModel : ViewModelBase
     partial void OnSelectedSortChanged(OptionItem value)
     {
         _config.Sort.Card = (CardSortOption)value.Value;
-        Refresh();
+
+        // A property setter cannot await; the refresh reports its own failures.
+        _ = RefreshOrReportAsync();
     }
 }

YKanBan/ViewModels/Dialogs/CardEditorDialogViewModel.cs

@@ -156,7 +156,18 @@ public sealed partial class CardEditorDialogViewModel : DialogViewModelBase
     [RelayCommand]
     private async Task AddTagAsync()
     {
-        var picker = new TagPickerDialogViewModel(_repository, Tags.Select(tag => tag.Tag.Id).ToHashSet());
+        TagPickerDialogViewModel picker;
+        try
+        {
+            picker = new TagPickerDialogViewModel(_repository, Tags.Select(tag => tag.Tag.Id).ToHashSet());
+        }
+        catch (Exception exception)
+        {
+            // The picker lists the tags as it opens; a read failure must not escape the command.
+            await _dialogs.ShowReadFailedAsync(exception);
+            return;
+        }
+
         if (await _dialogs.ShowAsync(picker) && picker.PickedTag is { } picked)
         {
             Tags.Add(new TagBadgeViewModel(picked));

YKanBan/ViewModels/Dialogs/IDialogService.cs

@@ -1,3 +1,5 @@
+using System.Diagnostics;
+
 namespace YKanBan.ViewModels.Dialogs;
 
 /// <summary>
@@ -47,4 +49,16 @@ public static class DialogServiceExtensions
     /// <returns>A task completing when the dialog closes.</returns>
     public static Task ShowMessageAsync(this IDialogService dialogs, string title, string message, string? details = null) =>
         dialogs.ShowAsync(new MessageDialogViewModel(title, message, details));
+
+    /// <summary>
+    /// Reports that reading from the workspace failed, so the view may be stale.
+    /// </summary>
+    /// <param name="dialogs">The dialog service.</param>
+    /// <param name="exception">The read failure; its untranslated message is shown as details.</param>
+    /// <returns>A task completing when the dialog closes.</returns>
+    public static Task ShowReadFailedAsync(this IDialogService dialogs, Exception exception)
+    {
+        Debug.WriteLine(exception);
+        return dialogs.ShowMessageAsync(Resources.Error_Read_Title, Resources.Error_Read_Message, exception.Message);
+    }
 }

YKanBan/ViewModels/Tags/TagsViewModel.cs

@@ -57,10 +57,12 @@ public sealed partial class TagsViewModel : ViewModelBase
     /// <summary>
     /// Reloads the tags with their usage counts.
     /// </summary>
+    /// <exception cref="Exception">Reading the workspace failed; the list is left unchanged.</exception>
     public void Refresh()
     {
+        IReadOnlyList<(TagModel Tag, long UsageCount)> tags = _repository.GetTagsWithUsage();
         Tags.Clear();
-        foreach ((TagModel tag, long usage) in _repository.GetTagsWithUsage())
+        foreach ((TagModel tag, long usage) in tags)
         {
             Tags.Add(new TagRowViewModel(this, tag, usage));
         }
@@ -68,6 +70,25 @@ public sealed partial class TagsViewModel : ViewModelBase
         OnPropertyChanged(nameof(IsEmpty));
     }
 
+    /// <summary>
+    /// Reloads like <see cref="Refresh"/>, but reports a read failure in a
+    /// message dialog instead of throwing.
+    /// </summary>
+    /// <returns><see langword="true"/> when the list was reloaded.</returns>
+    public async Task<bool> RefreshOrReportAsync()
+    {
+        try
+        {
+            Refresh();
+            return true;
+        }
+        catch (Exception exception)
+        {
+            await _dialogs.ShowReadFailedAsync(exception);
+            return false;
+        }
+    }
+
     /// <summary>
     /// Opens the new-tag dialog.
     /// </summary>
@@ -81,7 +102,7 @@ public sealed partial class TagsViewModel : ViewModelBase
             (name, color, description) => _repository.AddTag(name, color, description));
         if (await _dialogs.ShowAsync(dialog))
         {
-            AfterWrite();
+            await AfterWriteAsync();
         }
     }
 
@@ -98,7 +119,7 @@ public sealed partial class TagsViewModel : ViewModelBase
             (name, color, description) => _repository.UpdateTag(tag.Id, name, color, description));
         if (await _dialogs.ShowAsync(dialog))
         {
-            AfterWrite();
+            await AfterWriteAsync();
         }
     }
 
@@ -130,15 +151,19 @@ public sealed partial class TagsViewModel : ViewModelBase
             await _dialogs.ShowMessageAsync(
                 Resources.Error_Operation_Title, Resources.Error_Operation_Message, exception.Message);
         }
-        AfterWrite();
+        await AfterWriteAsync();
     }
 
     /// <summary>
-    /// Reloads the list and tells the board that tags changed.
+    /// Reloads the list and tells the board that tags changed; a failed reload
+    /// is reported and not announced.
     /// </summary>
-    private void AfterWrite()
+    /// <returns>A task completing after the reload.</returns>
+    private async Task AfterWriteAsync()
     {
-        Refresh();
-        TagsChanged?.Invoke(this, EventArgs.Empty);
+        if (await RefreshOrReportAsync())
+        {
+            TagsChanged?.Invoke(this, EventArgs.Empty);
+        }
     }
 }

YKanBan/ViewModels/WorkspaceViewModel.cs

@@ -45,8 +45,8 @@ public sealed partial class WorkspaceViewModel : ViewModelBase
         _dialogs = dialogs;
         Board = new BoardViewModel(session.Repository, config, dialogs);
         Tags = new TagsViewModel(session.Repository, config, dialogs);
-        Board.DataWritten += (_, _) => Tags.Refresh();
-        Tags.TagsChanged += (_, _) => Board.Refresh();
+        Board.DataWritten += async (_, _) => await Tags.RefreshOrReportAsync();
+        Tags.TagsChanged += async (_, _) => await Board.RefreshOrReportAsync();
     }
 
     /// <summary>