MAUI Hybrid-Blazor应用SQLite Error 14数据库无法打开问题求助

问题背景 #

连续两天卡在这个问题上：开发首个搭载本地SQLite数据库的MAUI Hybrid-Blazor应用时，触发错误SQLite Error 14: 'unable to open database file'，报错栈指向ServiceData.cs第26行。单独用控制台应用测试时，数据库连接和查询都正常运行，怀疑遗漏了MAUI专属配置。

相关代码 #

ServiceData.cs #

public class ServiceData
{
    private readonly string _connectionString;
    public ServiceData(string connectionString)
    {
        _connectionString = connectionString ?? throw new ArgumentNullException(nameof(connectionString));
    }

    public async Task<List<Cryptocurrency>?> GetAllCryptocurrenciesAsync()
    {
        try
        {
            var items = new List<Cryptocurrency>();

            using (var connection = new SqliteConnection(_connectionString))
            {
                await connection.OpenAsync();

                using (var command = connection.CreateCommand())
                {
                    command.CommandText = "SELECT * FROM cryptocurrencies;";

                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            var item = new Cryptocurrency
                            {
                                Id = reader.GetInt32(0),
                                Name = reader.GetString(1),
                                Icon = reader.GetString(2)
                            };
                            items.Add(item);
                        }
                    }
                }
            }

            return items;
        }
        catch (Exception ex)
        {
            string exceptionmsg = $"[*] - {ex.Message} - {ex.StackTrace} - [{DateTime.Now}]";
            return null;
        }
    }
}

MauiProgram.cs（原代码） #

public static class MauiProgram
{
    private static readonly string _databasePath = Path.Combine(FileSystem.AppDataDirectory, "Data/theboss.db");
    public static MauiApp CreateMauiApp()
    {
        var builder = MauiApp.CreateBuilder();
        builder
            .UseMauiApp<App>()
            .ConfigureFonts(fonts =>
            {
                fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
            });

        // Add SQLite connection
        var connectionStringBuilder = new SqliteConnectionStringBuilder
        {
            DataSource = $"Data Source= " + _databasePath
        };
        var connection = new SqliteConnection(connectionStringBuilder.ConnectionString);
        builder.Services.AddSingleton(connection);

        builder.Services.AddMauiBlazorWebView();

#if DEBUG
        builder.Services.AddBlazorWebViewDeveloperTools();
        builder.Logging.AddDebug();
#endif

        return builder.Build();
    }
}

已做排查（未解决） #

• 尝试路径：Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Data", "theboss.db")

  • 实际路径：/data/user/0/com.theboss.myapp/files/Data/theboss.db
  • 报错：Microsoft.Data.Sqlite.SqliteException (0x80004005): SQLite Error 14: 'unable to open database file'.

• 尝试路径：Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "theboss.db3")

  • 实际路径：/data/user/0/com.theboss.myapp/files/theboss.db3
  • 报错：Microsoft.Data.Sqlite.SqliteException (0x80004005): SQLite Error 1: 'no such table: cryptocurrencies'.

问题根源及修正方案 #

1. 连接字符串格式错误 #

原代码中SqliteConnectionStringBuilder.DataSource被错误拼接了"Data Source= "前缀，导致最终连接字符串变成Data Source= Data Source= /xxx/xxx.db的无效格式，直接去掉前缀即可。

2. 数据库目录未创建 #

FileSystem.AppDataDirectory下的Data文件夹默认不存在，SQLite无法在不存在的目录中创建数据库文件，需要手动创建目录。

3. 服务注册逻辑错误 #

直接注册SqliteConnection单例不合理，SQLite连接应随用随创建，建议注册ServiceData服务并传入正确的连接字符串。

修正后的MauiProgram.cs #

public static class MauiProgram
{
    public static MauiApp CreateMauiApp()
    {
        var builder = MauiApp.CreateBuilder();
        builder
            .UseMauiApp<App>()
            .ConfigureFonts(fonts =>
            {
                fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
            });

        // 创建数据库目录
        var dataDir = Path.Combine(FileSystem.AppDataDirectory, "Data");
        if (!Directory.Exists(dataDir))
        {
            Directory.CreateDirectory(dataDir);
        }
        var databasePath = Path.Combine(dataDir, "theboss.db");

        // 构建正确的连接字符串
        var connectionString = new SqliteConnectionStringBuilder
        {
            DataSource = databasePath,
            Mode = SqliteOpenMode.ReadWriteCreate // 不存在时自动创建数据库
        }.ConnectionString;

        // 注册ServiceData服务
        builder.Services.AddSingleton<ServiceData>(sp => new ServiceData(connectionString));

        builder.Services.AddMauiBlazorWebView();

#if DEBUG
        builder.Services.AddBlazorWebViewDeveloperTools();
        builder.Logging.AddDebug();
#endif

        return builder.Build();
    }
}

4. 预生成数据库部署（若使用现有数据库） #

如果theboss.db是预先创建好的数据库文件，需完成两步操作：

1. 将文件添加到项目中，设置复制到输出目录为如果较新则复制
2. 在应用启动时将文件从资源目录复制到目标路径，示例代码（可放在App.xaml.cs的OnStart方法中）：

var targetPath = Path.Combine(FileSystem.AppDataDirectory, "Data/theboss.db");
if (!File.Exists(targetPath))
{
    using var stream = await FileSystem.OpenAppPackageFileAsync("Data/theboss.db");
    using var outputStream = File.OpenWrite(targetPath);
    await stream.CopyToAsync(outputStream);
}

补充说明 #

第二个排查案例中出现no such table错误，是因为指定路径下无数据库文件，SQLite自动创建了空数据库，自然不存在cryptocurrencies表，解决上述路径和目录问题后即可避免。

内容的提问来源于stack exchange，提问作者Maryan