ASP.NET核心 - 執行命令時沒有找到密鑰

我試圖連接到本地數據庫 - 我可以使用localhost/phpmyadmin訪問 - 使用ASP.NET Core。我對這門語言很陌生，而且我正在努力解決與MySQL相關的異常問題。ASP.NET核心 - 執行命令時沒有找到密鑰

string constr = Configuration.GetSection("ConnectionStrings:con").Value; 
using (MySqlConnection con = new MySqlConnection(constr)) 
{ 
    string query = @"SELECT id 
        FROM `test`"; 
    using (MySqlCommand cmd = new MySqlCommand(query, con)) 
    { 
     con.Open(); 
     using (var sqlDataReader = cmd.ExecuteReader()) 
     { 
      while (sqlDataReader.Read()) 
      { 
       var id = sqlDataReader.GetInt32(0); 
      } 
     } 
     con.Close(); 
    } 
}

該異常發生在線路使用（VAR = SqlDataReader的cmd.ExecuteReader（））。

這是我的連接字符串：

"ConnectionStrings": { 
    "con": "Server=localhost;Database=musense;User=root;Password=********;Charset=utf8" 
}

我從appsettings.json內設置連接字符串。沒有字符集，我會得到一個例外，「'windows-1252'不是受支持的編碼名稱。」

在運行上面的代碼，我在該行得到下面的異常使用（VAR SqlDataReader的= cmd.ExecuteReader（））：

/home/memonick/Documents/Projects/musense/musense.csproj : warning NU1701: Package 'MySql.Data 6.9.9' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'. This package may not be fully compatible with your project. 
/home/memonick/Documents/Projects/musense/musense.csproj : warning NU1701: Package 'MySql.Data 6.9.9' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'. This package may not be fully compatible with your project. 

Unhandled Exception: System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary. 
    at System.ThrowHelper.ThrowKeyNotFoundException() 
    at System.Collections.Generic.Dictionary`2.get_Item(TKey key) 
    at MySql.Data.MySqlClient.MySqlField.SetFieldEncoding() 
    at MySql.Data.MySqlClient.NativeDriver.GetColumnData(MySqlField field) 
    at MySql.Data.MySqlClient.NativeDriver.GetColumnsData(MySqlField[] columns) 
    at MySql.Data.MySqlClient.Driver.GetColumns(Int32 count) 
    at MySql.Data.MySqlClient.ResultSet.LoadColumns(Int32 numCols) 
    at MySql.Data.MySqlClient.ResultSet..ctor(Driver d, Int32 statementId, Int32 numCols) 
    at MySql.Data.MySqlClient.Driver.NextResult(Int32 statementId, Boolean force) 
    at MySql.Data.MySqlClient.MySqlDataReader.NextResult() 
    at MySql.Data.MySqlClient.MySqlDataReader.Close() 
    at MySql.Data.MySqlClient.MySqlCommand.ResetReader() 
    at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior) 
    at musense.Startup.ConfigureServices(IServiceCollection services) in /home/memonick/Documents/Projects/musense/Startup.cs:line 46 
--- End of stack trace from previous location where exception was thrown --- 
    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() 
    at Microsoft.AspNetCore.Hosting.ConventionBasedStartup.ConfigureServices(IServiceCollection services) 
    at Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureApplicationServices() 
    at Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication() 
    at Microsoft.AspNetCore.Hosting.WebHostBuilder.Build() 
    at musense.Program.BuildWebHost(String[] args) in /home/memonick/Documents/Projects/musense/Program.cs:line 21 
    at musense.Program.Main(String[] args) in /home/memonick/Documents/Projects/musense/Program.cs:line 17

值得一提的是，正在建立連接。因此，例如，我可以更新一行或執行SELECT VERSION（）。只有當我嘗試在ASP.NET Core的表上執行SELECT語句時，纔會出現問題。聲明本身似乎是有效的，因爲它通常在phpmyadmin中執行。

測試表有以下模式：

CREATE TABLE IF NOT EXISTS `test` (
    `id` int(11) NOT NULL, 
    `value` int(11) NOT NULL, 
    PRIMARY KEY (`id`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_swedish_ci;

我已經試過各種排序規則，但仍存在例外。歡迎任何幫助！

來源

2017-09-02 MemoNick

MySQL連接器返回一個可以與DBNull.Value進行比較的值。它看起來像數據庫從記錄返回空值。 – Adrian

@AnirudhaGupta哪個連接器應該返回一個值？ – MemoNick

我認爲這是你的主鍵，它是否存在。因爲如果它是空的，它將會產生類型轉換異常，並且你的異常提示沒有任何東西返回0索引。 – Adrian

您的問題上升的事實，您使用的是NuGet包不兼容.NETCoreApp2.0：

/home/memonick/Documents/Projects/musense/musense.csproj : warning NU1701: Package 'MySql.Data 6.9.9' was restored using '.NETFramework,Version=v4.6.1' instead of the project target framework '.NETCoreApp,Version=v2.0'. This package may not be fully compatible with your project.

您需要升級MySql.Data 6.9.9和使用至少6.10.3-rc版本（記得檢查節目搶鮮包在nuget瀏覽器），與.netstandard1.3及以上（含.NETCoreApp2.0）兼容。

來源

2017-09-02 16:12:11

ASP.NET核心 - 執行命令時沒有找到密鑰

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