.net MVC 4 Web API服务连接到SQL Server问题

Question

The setup

We have a .net mvc 4 web api service layer, that is accessed via a web app, which gets data from a SQL Server 2008 database.

The problem

When more than 5 GET requests are being made to the web service at the same time, a 500 Interal Server Error is returned to the web app. When I look closer at the .net error I see the following:

An error has occurred.
The connection was not closed. The connection's current state is open

The C# service code where the exception is being thrown:

public class ImageLinkRepository : IImageLinkRepository
{
  private SqlConnection cnnSQL = new SqlConnection(...);

  public IEnumerable<ImageLink> Get(String userId)
        {

            ImageLinks = new List<ImageLink>();

            // open connection to DB
            cnnSQL.Open();

            try
            {
                SqlCommand cmmSQL = new SqlCommand("nVision_select_lcimagelinks_sp", cnnSQL);
                cmmSQL.CommandType = System.Data.CommandType.StoredProcedure;

                SqlParameter prmSQL = cmmSQL.Parameters.Add(new SqlParameter
                {
                    ParameterName = "@LCIMGLINKUSERID",
                    Value = userId
                });

                SqlDataReader rdrSQL = cmmSQL.ExecuteReader();

                if (rdrSQL.HasRows)
                {
                    while (rdrSQL.Read())
                    {
                        ImageLinks.Add(new ImageLink 
                        { 
                            // set new ImageLink object's properties    
                            imageTopicId = DBReader.SQLString(rdrSQL, "LCIMGLINKIMGTOPICID"), 
                            id = DBReader.SQLInt(rdrSQL, "LCIMGLINKPK"),
                            recordId = DBReader.SQLString(rdrSQL, "LCIMGLINKRECORDID"),
                            text = DBReader.SQLString(rdrSQL, "LCIMGLINKTEXT"),
                            topicId = DBReader.SQLString(rdrSQL, "LCIMGLINKTOPICID"),
                            topicItem = DBReader.SQLString(rdrSQL, "LCIMGLINKTOPICITEM"),
                            url = DBReader.SQLString(rdrSQL, "LCIMGLINKURL"),
                            user = DBReader.SQLString(rdrSQL, "LCIMGLINKUSERID")
                        });
                    }
                }    
            }

            // close connection to DB
            cnnSQL.Close();

            return ImageLinks;
        }
}

I have tried to manually close the connection if it is open and I have tried to only open the connection if its closed, neither of them work.

I must be doing something wrong, surely, the service should be able to handle simultaneous requests. What am I missing?

Answer 1

You're likely exhausting the SQL Connection Pool. To start with you should be wrapping your SqlCommand , SqlConnection , and SqlReaders with using() statements to ensure they are correctly disposed of and closed.

The SqlConnection being constructed as a field means that your controller has to be responsible for Disposing of it. It's easier to construct it within the method, where it can be wrapped in a using() as well (otherwise you're class should implement IDisposable() , calling .Dispose() on the Connection in turn).

try
{
  using (var cnnSQL = new SqlConnection(...))
  {
    using (var cmmSQL = new SqlCommand("nVision_select_lcimagelinks_sp", cnnSQL))
    {
      cmmSQL.CommandType = System.Data.CommandType.StoredProcedure;

      SqlParameter prmSQL = cmmSQL.Parameters.Add(new SqlParameter
      {
          ParameterName = "@LCIMGLINKUSERID",
          Value = userId
      });

      using (var rdrSQL = cmmSQL.ExecuteReader())
      {
      ...
      }
    }
  {
} ...