Fix Race conditions, thread-safety issues, and code quality in Developer Balance sample

10.0/Apps/DeveloperBalance/AppShell.xaml.cs

@@ -16,7 +16,7 @@ public AppShell()
 	}
 	public static async Task DisplaySnackbarAsync(string message)
 	{
-		CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
+		using var cancellationTokenSource = new CancellationTokenSource(TimeSpan.FromSeconds(5));
 
 		var snackbarOptions = new SnackbarOptions
 		{
@@ -41,7 +41,7 @@ public static async Task DisplayToastAsync(string message)
 
 		var toast = Toast.Make(message, textSize: 18);
 
-		var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
+		using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(5));
 		await toast.Show(cts.Token);
 	}
 

10.0/Apps/DeveloperBalance/Data/CategoryRepository.cs

@@ -10,6 +10,7 @@ namespace DeveloperBalance.Data;
 public class CategoryRepository
 {
 	private bool _hasBeenInitialized = false;
+	private readonly SemaphoreSlim _initLock = new(1, 1);
 	private readonly ILogger _logger;
 
 	/// <summary>
@@ -29,11 +30,15 @@ private async Task Init()
 		if (_hasBeenInitialized)
 			return;
 
-		await using var connection = new SqliteConnection(Constants.DatabasePath);
-		await connection.OpenAsync();
-
+		await _initLock.WaitAsync();
 		try
 		{
+			if (_hasBeenInitialized)
+				return;
+
+			await using var connection = new SqliteConnection(Constants.DatabasePath);
+			await connection.OpenAsync();
+
 			var createTableCmd = connection.CreateCommand();
 			createTableCmd.CommandText = @"
             CREATE TABLE IF NOT EXISTS Category (
@@ -42,14 +47,18 @@ CREATE TABLE IF NOT EXISTS Category (
                 Color TEXT NOT NULL
             );";
 			await createTableCmd.ExecuteNonQueryAsync();
+
+			_hasBeenInitialized = true;
 		}
 		catch (Exception e)
 		{
 			_logger.LogError(e, "Error creating Category table");
 			throw;
 		}
-
-		_hasBeenInitialized = true;
+		finally
+		{
+			_initLock.Release();
+		}
 	}
 
 	/// <summary>
@@ -171,14 +180,22 @@ public async Task<int> DeleteItemAsync(Category item)
 	/// </summary>
 	public async Task DropTableAsync()
 	{
-		await Init();
-		await using var connection = new SqliteConnection(Constants.DatabasePath);
-		await connection.OpenAsync();
+		await _initLock.WaitAsync();
+		try
+		{
+			await using var connection = new SqliteConnection(Constants.DatabasePath);
+			await connection.OpenAsync();
 
-		var dropTableCmd = connection.CreateCommand();
-		dropTableCmd.CommandText = "DROP TABLE IF EXISTS Category";
+			var dropTableCmd = connection.CreateCommand();
+			dropTableCmd.CommandText = "DROP TABLE IF EXISTS Category";
 
-		await dropTableCmd.ExecuteNonQueryAsync();
-		_hasBeenInitialized = false;
+			await dropTableCmd.ExecuteNonQueryAsync();
+
+			_hasBeenInitialized = false;
+		}
+		finally
+		{
+			_initLock.Release();
+		}
 	}
 }

10.0/Apps/DeveloperBalance/Data/JsonContext.cs

@@ -1,6 +1,8 @@
 using System.Text.Json.Serialization;
 using DeveloperBalance.Models;
 
+namespace DeveloperBalance.Data;
+
 [JsonSerializable(typeof(Project))]
 [JsonSerializable(typeof(ProjectTask))]
 [JsonSerializable(typeof(ProjectsJson))]

10.0/Apps/DeveloperBalance/Data/ProjectRepository.cs

@@ -10,6 +10,7 @@ namespace DeveloperBalance.Data;
 public class ProjectRepository
 {
 	private bool _hasBeenInitialized = false;
+	private readonly SemaphoreSlim _initLock = new(1, 1);
 	private readonly ILogger _logger;
 	private readonly TaskRepository _taskRepository;
 	private readonly TagRepository _tagRepository;
@@ -35,11 +36,15 @@ private async Task Init()
 		if (_hasBeenInitialized)
 			return;
 
-		await using var connection = new SqliteConnection(Constants.DatabasePath);
-		await connection.OpenAsync();
-
+		await _initLock.WaitAsync();
 		try
 		{
+			if (_hasBeenInitialized)
+				return;
+
+			await using var connection = new SqliteConnection(Constants.DatabasePath);
+			await connection.OpenAsync();
+
 			var createTableCmd = connection.CreateCommand();
 			createTableCmd.CommandText = @"
             CREATE TABLE IF NOT EXISTS Project (
@@ -50,14 +55,18 @@ CREATE TABLE IF NOT EXISTS Project (
                 CategoryID INTEGER NOT NULL
             );";
 			await createTableCmd.ExecuteNonQueryAsync();
+
+			_hasBeenInitialized = true;
 		}
 		catch (Exception e)
 		{
 			_logger.LogError(e, "Error creating Project table");
 			throw;
 		}
-
-		_hasBeenInitialized = true;
+		finally
+		{
+			_initLock.Release();
+		}
 	}
 
 	/// <summary>
@@ -87,10 +96,19 @@ public async Task<List<Project>> ListAsync()
 			});
 		}
 
+		// Fetch all tasks and all tags in one query each, then assign in memory.
+		// This reduces 2N+1 queries to 3 regardless of project count.
+		var allTasks = await _taskRepository.ListAsync();
+		var allTagsByProject = await _tagRepository.ListAllByProjectAsync();
+
+		var tasksByProject = allTasks
+			.GroupBy(t => t.ProjectID)
+			.ToDictionary(g => g.Key, g => g.ToList());
+
 		foreach (var project in projects)
 		{
-			project.Tags = await _tagRepository.ListAsync(project.ID);
-			project.Tasks = await _taskRepository.ListAsync(project.ID);
+			project.Tasks = tasksByProject.TryGetValue(project.ID, out var tasks) ? tasks : [];
+			project.Tags = allTagsByProject.TryGetValue(project.ID, out var tags) ? tags : [];
 		}
 
 		return projects;
@@ -197,16 +215,24 @@ public async Task<int> DeleteItemAsync(Project item)
 	/// </summary>
 	public async Task DropTableAsync()
 	{
-		await Init();
-		await using var connection = new SqliteConnection(Constants.DatabasePath);
-		await connection.OpenAsync();
+		await _initLock.WaitAsync();
+		try
+		{
+			await using var connection = new SqliteConnection(Constants.DatabasePath);
+			await connection.OpenAsync();
+
+			var dropCmd = connection.CreateCommand();
+			dropCmd.CommandText = "DROP TABLE IF EXISTS Project";
+			await dropCmd.ExecuteNonQueryAsync();
 
-		var dropCmd = connection.CreateCommand();
-		dropCmd.CommandText = "DROP TABLE IF EXISTS Project";
-		await dropCmd.ExecuteNonQueryAsync();
+			_hasBeenInitialized = false;
+		}
+		finally
+		{
+			_initLock.Release();
+		}
 
 		await _taskRepository.DropTableAsync();
 		await _tagRepository.DropTableAsync();
-		_hasBeenInitialized = false;
 	}
 }

10.0/Apps/DeveloperBalance/Data/SeedDataService.cs

@@ -24,7 +24,7 @@ public SeedDataService(ProjectRepository projectRepository, TaskRepository taskR
 
 	public async Task LoadSeedDataAsync()
 	{
-		ClearTables();
+		await ClearTables();
 
 		await using Stream templateStream = await FileSystem.OpenAppPackageFileAsync(_seedDataFilePath);
 
@@ -83,19 +83,9 @@ public async Task LoadSeedDataAsync()
 		}
 	}
 
-	private async void ClearTables()
+	private async Task ClearTables()
 	{
-		try
-		{
-			await Task.WhenAll(
-				_projectRepository.DropTableAsync(),
-				_taskRepository.DropTableAsync(),
-				_tagRepository.DropTableAsync(),
-				_categoryRepository.DropTableAsync());
-		}
-		catch (Exception e)
-		{
-			Console.WriteLine(e);
-		}
+		await _projectRepository.DropTableAsync();
+		await _categoryRepository.DropTableAsync();
 	}
 }

10.0/Apps/DeveloperBalance/Data/TagRepository.cs

@@ -10,6 +10,7 @@ namespace DeveloperBalance.Data;
 public class TagRepository
 {
 	private bool _hasBeenInitialized = false;
+	private readonly SemaphoreSlim _initLock = new(1, 1);
 	private readonly ILogger _logger;
 
 	/// <summary>
@@ -29,11 +30,15 @@ private async Task Init()
 		if (_hasBeenInitialized)
 			return;
 
-		await using var connection = new SqliteConnection(Constants.DatabasePath);
-		await connection.OpenAsync();
-
+		await _initLock.WaitAsync();
 		try
 		{
+			if (_hasBeenInitialized)
+				return;
+
+			await using var connection = new SqliteConnection(Constants.DatabasePath);
+			await connection.OpenAsync();
+
 			var createTableCmd = connection.CreateCommand();
 			createTableCmd.CommandText = @"
             CREATE TABLE IF NOT EXISTS Tag (
@@ -50,14 +55,18 @@ CREATE TABLE IF NOT EXISTS ProjectsTags (
                 PRIMARY KEY(ProjectID, TagID)
             );";
 			await createTableCmd.ExecuteNonQueryAsync();
+
+			_hasBeenInitialized = true;
 		}
 		catch (Exception e)
 		{
 			_logger.LogError(e, "Error creating tables");
 			throw;
 		}
-
-		_hasBeenInitialized = true;
+		finally
+		{
+			_initLock.Release();
+		}
 	}
 
 	/// <summary>
@@ -88,6 +97,46 @@ public async Task<List<Tag>> ListAsync()
 		return tags;
 	}
 
+	/// <summary>
+	/// Retrieves all tags grouped by their associated project ID in a single query.
+	/// </summary>
+	/// <returns>A dictionary mapping project ID to its list of <see cref="Tag"/> objects.</returns>
+	public async Task<Dictionary<int, List<Tag>>> ListAllByProjectAsync()
+	{
+		await Init();
+		await using var connection = new SqliteConnection(Constants.DatabasePath);
+		await connection.OpenAsync();
+
+		var selectCmd = connection.CreateCommand();
+		selectCmd.CommandText = @"
+        SELECT t.ID, t.Title, t.Color, pt.ProjectID
+        FROM Tag t
+        JOIN ProjectsTags pt ON t.ID = pt.TagID";
+
+		var result = new Dictionary<int, List<Tag>>();
+
+		await using var reader = await selectCmd.ExecuteReaderAsync();
+		while (await reader.ReadAsync())
+		{
+			var tag = new Tag
+			{
+				ID = reader.GetInt32(0),
+				Title = reader.GetString(1),
+				Color = reader.GetString(2)
+			};
+			var projectID = reader.GetInt32(3);
+
+			if (!result.TryGetValue(projectID, out var list))
+			{
+				list = [];
+				result[projectID] = list;
+			}
+			list.Add(tag);
+		}
+
+		return result;
+	}
+
 	/// <summary>
 	/// Retrieves a list of tags associated with a specific project.
 	/// </summary>
@@ -105,7 +154,7 @@ SELECT t.*
         FROM Tag t
         JOIN ProjectsTags pt ON t.ID = pt.TagID
         WHERE pt.ProjectID = @ProjectID";
-		selectCmd.Parameters.AddWithValue("ProjectID", projectID);
+		selectCmd.Parameters.AddWithValue("@ProjectID", projectID);
 
 		var tags = new List<Tag>();
 
@@ -288,17 +337,24 @@ public async Task<int> DeleteItemAsync(Tag item, int projectID)
 	/// </summary>
 	public async Task DropTableAsync()
 	{
-		await Init();
-		await using var connection = new SqliteConnection(Constants.DatabasePath);
-		await connection.OpenAsync();
+		await _initLock.WaitAsync();
+		try
+		{
+			await using var connection = new SqliteConnection(Constants.DatabasePath);
+			await connection.OpenAsync();
 
-		var dropTableCmd = connection.CreateCommand();
-		dropTableCmd.CommandText = "DROP TABLE IF EXISTS Tag";
-		await dropTableCmd.ExecuteNonQueryAsync();
+			var dropTableCmd = connection.CreateCommand();
+			dropTableCmd.CommandText = "DROP TABLE IF EXISTS Tag";
+			await dropTableCmd.ExecuteNonQueryAsync();
 
-		dropTableCmd.CommandText = "DROP TABLE IF EXISTS ProjectsTags";
-		await dropTableCmd.ExecuteNonQueryAsync();
+			dropTableCmd.CommandText = "DROP TABLE IF EXISTS ProjectsTags";
+			await dropTableCmd.ExecuteNonQueryAsync();
 
-		_hasBeenInitialized = false;
+			_hasBeenInitialized = false;
+		}
+		finally
+		{
+			_initLock.Release();
+		}
 	}
 }