Question

所以基本上我有一个Soap webservice，可以从SqlServer数据库中插入和检索一些数据。

webservice使用负责数据库内容的Singleton。

public class Service : System.Web.Services.WebService
{
    private DBAccess dbaccess;
    public Service()
    {
        dbaccess = DBAccessLocalhost.GetInstance();
    }

    [WebMethod]
    public List<Profile> XXX(Guid a, uint b, DateTime c)
    {
        return dbaccess.XXX(a, b, c);
    }
    ...
}

访问数据库的单例。它有很多方法基本上都可以做到这一点。

public class DBAccessLocalhost : DBAccess
{
    private static DBAccess instance = null;
    private string connectionString;

    public static DBAccess GetInstance()
    {
        if (instance == null)
            instance = new DBAccessLocalhost();

        return instance;
    }

    private DBAccessLocalhost()
    {
        connectionString = "Data Source=localhost;Initial Catalog=DBName;Integrated Security=True;Max Pool Size=2000;Pooling=false";
    }

    public override void XXX(Guid a, uint b, DateTime c)
    {
        SqlCommand cmd;
        SqlDataReader dr;
        string strSql = "SP_Name";
        SqlConnection conn;
        conn = new SqlConnection(connectionString);

        try
        {
            conn.Open();

            cmd = new SqlCommand(strSql, conn);
            cmd.CommandType = System.Data.CommandType.StoredProcedure;

            cmd.Parameters.AddWithValue("@a", a.ToString());
            cmd.Parameters.AddWithValue("@b", (int)b);
            cmd.Parameters.AddWithValue("@c", c);
            dr = cmd.ExecuteReader();

            while (dr.Read() && dr.HasRows)
            {
                //Do stuff...
            }

            dr.Close();

        }catch (Exception ex)
        {
            throw new DBError("Errors: " + ex.Message);
        }
        finally
        {
            conn.Close();
        }
     }

第二版：

public class DBAccessLocalhost : DBAccess
{
    private static DBAccess instance = null;
    private string connectionString;

    public static DBAccess GetInstance()
    {
        if (instance == null)
            instance = new DBAccessLocalhost();

        return instance;
    }

    private DBAccessLocalhost()
    {
        connectionString = "Data Source=localhost;Initial Catalog=DBName;Integrated Security=True;Max Pool Size=2000;Pooling=true";
    }

    public override void XXX(Guid a, uint b, DateTime c)
    {
        string strSql = "SP_Name";

        using (SqlConnection conn = new SqlConnection(connectionString))
        {
            using (SqlCommand cmd = new SqlCommand(strSql, conn))
            {
                cmd.CommandType = System.Data.CommandType.StoredProcedure;

                cmd.Parameters.AddWithValue("@a", a.ToString());
                cmd.Parameters.AddWithValue("@b", (int)b);
                cmd.Parameters.AddWithValue("@c", c);

                try
                {
                    conn.Open();

                    using (SqlDataReader dr = cmd.ExecuteReader())
                    {
                        while (dr.Read())
                        {
                            //....
                        }
                    }
                }
                catch (Exception ex)
                {
                    throw new DBError("Error: " + ex.Message);
                }
                finally
                {
                    conn.Close();
                }
            }
        }

问题是有时我会遇到这个例外：

 DBAccessWebSerice,System.ServiceModel.FaultException: Server was unable to process 
 request. ---> Errors: ExecuteNonQuery requires an open and available    
 Connection. The connection's current state is closed (Sometimes says connecting).

 Server stack trace: 
 at System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime 
 operation, ProxyRpc& rpc)
 at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, 
 ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
 at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage  
 methodCall, ProxyOperationRuntime operation)
 at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)

问题可能是因为数据库同时存在多个连接？

可能这不是最好的办法。但是，如果您有更好的方法来解决这个问题，请说明一下。

Answer 1

Singleton不是Db Access的好模式。使用静态方法检索数据。最有可能的是，您的问题是2个线程访问了您的实例，并且您无法阻止它。其他要点：

不要使用“SP_”前缀
在处理诸如datareader

using

使用连接池

我发现您在此处提供的代码中存在各种问题的可能性。例如，如果读取datareader错误，则不会清除资源。

这是一种方式：

public override void XXX(Guid a, uint b, DateTime c)
{
    string strSql = "SP_Name";
    lock (lockObject) {  // lock the code for the duration of execution so it is thread safe now (because you in singleton) 
// But this is bad for DB access !!!! What if SP executes long - other threads have to wait
// Use simple static methods for data access and no `lock`
        using (SqlConnection conn = new SqlConnection(connectionString))
        {
            conn.Open();
            using (SqlCommand cmd = new SqlCommand(strSql, conn))
            {
                cmd.CommandType = System.Data.CommandType.StoredProcedure;

                cmd.Parameters.AddWithValue("@a", a.ToString());
                cmd.Parameters.AddWithValue("@b", (int)b);
                cmd.Parameters.AddWithValue("@c", c);
                // no need for any `try-catch` here because `using` is that and `finally`
                using (SqlDataReader dr = cmd.ExecuteReader())
                {
                    while (dr.Read())
                    {
                        //....
                    }
                }

            }
            conn.Close();
        }
    }
}

其他选项，如果您希望更好地控制异常处理，则使用try-catch-finally代替using。然后，最后，您将执行另一个try-catch来清理资源。 //伪代码

try
       connection
       command
       datareader
   catch (Exception ex)
       prepare user message
       log or
       throw/throw new, etc // depends. This is Webservice, may be log and response with error message
   finally
       try
          if datareader alive
             close datareader 
             dispose datareader 
       catch // do nothing here
       try
          if command alive
             dispose command
       catch // do nothing here
       try
          if connection alive
             close connection 
             dispose connection 
       catch // do nothing here

Answer 2

这是一种方法，放弃单身人士的想法，正如另一个答案所暗示的那样：

将Func传递给您的服务，该服务是数据访问对象的工厂

让DBAccess实现IDisposable并使用using块

public class Service : System.Web.Services.WebService
{
   private Func<DBAccess> getDBAccess;

   public Service(Func<DBAccess> getDBAccess)
   {
      this.getDBAccess = getDBAccess;
   }

   [WebMethod]
   public List<Profile> XXX(Guid a, uint b, DateTime c)
   {
        using(var dbaccess = this.getDBAccess())
        {
            return dbaccess.XXX(a, b, c);
        }  
   }
   ...
 }

具有数据库访问权限的Soap Web Service

2 个答案: