使用DataSet

Question

有一个MVC Web应用程序，它有一个用ADO.NET实现的模块。 控制器代码如下：

private List<CustomTabModel> GenerateReports(ReportModel oViewModel)
{
    List<CentralDbCase> Cases = AppController.Instance.Prov.Cases(a, b, c, InitiativeTypes(submissionYear), includedDataSource, namePrefix, out message);

   //other code

    return DoWork(Cases);
}       
private List<CustomTabModel> DoWork(List<CentralDbCase> Cases)
{
   //other code
}

当尝试连接到SQL数据库时，当两个或更多人同时连接到应用程序时，我收到以下错误：

ExecuteReader需要一个开放且可用的连接。连接的当前状态已打开。

以下是Business Classes，我正在使用此模块： 1个Provider.cs（在BusinessLayer文件夹中）

public List<CentralDbCase> Cases(string a, int b, List<KeyValuePair<string, string>> c, List<string> SelectedTypes, string includedDataSource, string NamePrefix, out string message)
        {            
            List<CentralDbCase> theList = new List<CentralDbCase>();

            string sql = (AppController.Instance.DbConnection is System.Data.SqlClient.SqlConnection) ? ListCaseSqlEx(a, b, c) : ListCaseSql(a, b, c);

            IDbCommand cmd = DbHelper.NewCommandForConnection(AppController.Instance.DbConnection, sql);
            IDbDataAdapter da = DbHelper.NewDataAdapterForConnection(AppController.Instance.DbConnection);
            da.SelectCommand = cmd;

            DataSet ds = new DataSet();
            ds.CaseSensitive = true;

            da.Fill(ds);  //--getting error here--

            //other line of code

            return theList;
        }

2 ICentralDbProvider.cs（在BusinessLayer文件夹中）

namespace PJ.Business
{
    public interface ICentralDbProvider
    {
        List<CentralDbCase> Cases(string a, int b, List<KeyValuePair<string,string>> c, 
            List<string> SelectedTypes, string includedDataSource, string NamePrefix, out string message);

        Dictionary<string, string> ListNames(int submissionYear);

        VariableInfo[] VariableTypes { get; }

        DataTable GetDataTable(int submissionYear, string scenario, TableName tableName, string tablePrefix, string whereClause, string includedDataSource);        
    }
}

3 AppController.cs（在BusinessLayer文件夹中）

namespace PJ.Business
{
    public class AppController
    {
        IDbConnection dbConnection;
        ICentralDbProvider cdbProv;

        public static AppController Instance
        {
            get
            {
                if (_appController == null)
                {
                    _appController = new AppController();
                }
                return _appController;
            }
        }

        public void InitConnection()
        {
            string connString = ConfigurationManager.ConnectionStrings["ABC_Connection"].ConnectionString;
            string provider = ConfigurationManager.ConnectionStrings["ABC_Connection"].ProviderName;

            if (provider == EnumHelper.GetDescription(Provider.SQL))
            {
                dbConnection = new System.Data.SqlClient.SqlConnection(connString);                
            }
            else if (provider == EnumHelper.GetDescription(Provider.Oracle))
            {
                dbConnection = new System.Data.OracleClient.OracleConnection(connString);
            }
            else
            {
                throw new Exception("Invalid Connection");
            }
        }

        public IDbConnection DbConnection
        {
            get { return dbConnection; }
            set { dbConnection = value; }
        }

        public ICentralDbProvider Prov
        {
            get { return cdbProv; }
            set { cdbProv = value; }
        }

    }
}

4 DbHelper.cs（在BusinessLayer文件夹内）

namespace PJ.Business
{
    internal static class DbHelper
    {
        public static IDbCommand NewCommandForConnection(IDbConnection conn, string commandText)
        {
            IDbCommand cmd = NewCommandForConnection(conn);
            cmd.CommandText = commandText;
            return cmd;
        }

        public static IDbCommand NewCommandForConnection(IDbConnection conn)
        {
            IDbCommand cmd;
            if (conn is OracleConnection)
            {
                cmd = new OracleCommand();
            }
            else if (conn is SqlConnection)
            {
                cmd = new SqlCommand();
            }
            else
            {
                throw new Exception("Incorrect Connection class currently in use.");
            }
            cmd.Connection = conn;
            return cmd;
        }

        public static IDbDataAdapter NewDataAdapterForConnection(IDbConnection conn)
        {
            IDbDataAdapter da;
            if (conn is OracleConnection)
            {
                da = new OracleDataAdapter();
            }
            else if (conn is SqlConnection)
            {
                da = new SqlDataAdapter();
            }
            else
            {
                throw new Exception("Incorrect Connection class currently in use.");
            }

            return da;
        }
    }
}

注意：此模块使用Singelton Pattern。请告诉我代码中的错误。 提前致谢

编辑：堆栈跟踪

  

System.Data.SqlClient.SqlConnection.GetOpenConnection（String method）   System.Data.SqlClient.SqlConnection.ValidateConnectionForExecute（字符串   方法，SqlCommand命令）   System.Data.SqlClient.SqlCommand.ValidateCommand（String方法，   布尔异步）   System.Data.SqlClient.SqlCommand.RunExecuteReader（的CommandBehavior   cmdBehavior，RunBehavior runBehavior，Boolean returnStream，String   方法，TaskCompletionSource`1完成，Int32超时，任务＆amp;任务，   布尔asyncWrite）   System.Data.SqlClient.SqlCommand.RunExecuteReader（的CommandBehavior   cmdBehavior，RunBehavior runBehavior，Boolean returnStream，String   方法）System.Data.SqlClient.SqlCommand.ExecuteReader（CommandBehavior   行为，字符串方法）   System.Data.SqlClient.SqlCommand.ExecuteDbDataReader（的CommandBehavior   行为）   System.Data.Common.DbCommand.System.Data.IDbCommand.ExecuteReader（的CommandBehavior   行为）System.Data.Common.DbDataAdapter.FillInternal（DataSet   dataset，DataTable [] datatables，Int32 startRecord，Int32 maxRecords，   String srcTable，IDbCommand命令，CommandBehavior行为）   System.Data.Common.DbDataAdapter.Fill（DataSet dataSet，Int32   startRecord，Int32 maxRecords，String srcTable，IDbCommand命令，   CommandBehavior行为）   System.Data.Common.DbDataAdapter.Fill（DataSet dataSet）   PJ.Business.Provider.Cases（字符串a，int b，List＆gt; c，List SelectedTypes，string includedDataSource，   in string namePrefix，out string message）in   c：\ Temp \ PJ.Business \ Provider.cs：第952行   PJ.WebClient.Areas.Tool.Controllers.ReportController.GenerateReports（ReportModel   oViewModel）in   C：\ TEMP \ PJ.WebClient \区\工具\ \控制器ReportController.cs：行   213 at   PJ.WebClient.Areas.Tool.Controllers.ReportController.Index（ReportModel   m）in   C：\ TEMP \ PJ.WebClient \区\工具\ \控制器ReportController.cs：行   154