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我试图连接到本地数据库 - 我可以使用localhost/phpmyadmin访问 - 使用ASP.NET Core。我对这门语言很陌生，而且我正在努力解决与MySQL相关的异常问题。ASP.NET核心 - 执行命令时没有找到密钥
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();
}
}
该异常发生在线路使用（VAR = SqlDataReader的cmd.ExecuteReader（））。
这是我的连接字符串：
"ConnectionStrings": {
"con": "Server=localhost;Database=musense;User=root;Password=********;Charset=utf8"
}
我从appsettings.json内设置连接字符串。没有字符集，我会得到一个例外，“'windows-1252'不是受支持的编码名称。”
在运行上面的代码，我在该行得到下面的异常使用（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，正在建立连接。因此，例如，我可以更新一行或执行SELECT VERSION（）。只有当我尝试在ASP.NET Core的表上执行SELECT语句时，才会出现问题。声明本身似乎是有效的，因为它通常在phpmyadmin中执行。
测试表有以下模式：
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;
我已经试过各种排序规则，但仍存在例外。欢迎任何帮助！
MySQL连接器返回一个可以与DBNull.Value进行比较的值。它看起来像数据库从记录返回空值。 – Adrian
@AnirudhaGupta哪个连接器应该返回一个值？ – MemoNick
我认为这是你的主键，它是否存在。因为如果它是空的，它将会产生类型转换异常，并且你的异常提示没有任何东西返回0索引。 – Adrian