ASP.NET核心 - 执行命令时找不到密钥

I'm trying to connect to my local database - which I can access using localhost/phpmyadmin - using ASP.NET Core. I'm new to the language, and I am struggling with a MySQL-related exception.

我正在尝试使用ASP.NET Core连接到我的本地数据库 - 我可以使用localhost / phpmyadmin访问它。我是这门语言的新手，我正在努力解决与MySQL相关的异常问题。

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();
    }
}

The exception happens at the line using (var sqlDataReader = cmd.ExecuteReader()).

使用（var sqlDataReader = cmd.ExecuteReader（））的行发生异常。

This is my connection string:

这是我的连接字符串：

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

I am setting the connection string from within the appsettings.json. Without the charset, I get an exception that "'windows-1252' is not a supported encoding name."

我在appsettings.json中设置连接字符串。没有charset，我得到一个例外，“'windows-1252'不是受支持的编码名称。”

Upon running the above code, I get the following exception at the line using (var sqlDataReader = cmd.ExecuteReader()).:

运行上面的代码后，我在使用（var sqlDataReader = cmd.ExecuteReader（））的行中得到以下异常：

/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

It's worth noting that the connection is being established. Thus, for example, I can update a row, or execute SELECT VERSION(). The problem happens only when I try to execute a SELECT statement on a table from ASP.NET Core. The statement itself seems valid, as it executes normally in phpmyadmin.

值得注意的是，正在建立连接。因此，例如，我可以更新一行，或执行SELECT VERSION（）。只有当我尝试从ASP.NET Core对表执行SELECT语句时才会出现此问题。语句本身似乎有效，因为它在phpmyadmin中正常执行。

The test table has the following schema:

测试表具有以下模式：

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;

I've tried various collations, but the exception persists. Any help is welcome!

我尝试了各种排序规则，但例外情况仍然存在。欢迎任何帮助！

1 个解决方案

#1

Your issue rises by the fact that you are using a NuGet package not compatible with .NETCoreApp2.0:

您使用与.NETCoreApp2.0不兼容的NuGet包时，问题就出现了：

/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.

You need to upgrade MySql.Data 6.9.9 and use at least 6.10.3-rc version (remember to check show prerelease packages in nuget browser), which is compatible with .netstandard1.3 and above (including .NETCoreApp2.0).

您需要升级MySql.Data 6.9.9并使用至少6.10.3-rc版本（记得检查nuget浏览器中的show prerelease软件包），它与.netstandard1.3及更高版本（包括.NETCoreApp2.0）兼容。