C＃将侦听器附加到Npgsql连接

Question

I'm building an app in C# that use npgsql connection for queries in postgres database. I want to know if there is a way to be notified at all steps of query execution; I mean i want to receive messages :

• "open" : when connection is open
• "connecting" : when connection is connecting
• "executing" : when connection is executing
• "close" : when query is executed and connection closed

Is there a way to do that ?

Answer 1

You can do this, but you have to trigger the notifications yourself. It is doable and even easy. In ADO.NET you have code flow similar to:

DbProviderFactory factory = DbProviderFactories.GetFactory("Npgsql");
using(DbConnection con = factory.CreateConnection()) 
{
      con.ConnectionString = ConfigurationManager.AppSettings[connectionName];
      con.Open();  
      // Connection is open, notify user
      DbCommand cmd = connection.CreateCommand();
      cmd.CommandText = query; 

      // Query execution is going to start, add code to inform user
      cmd.ExecuteXXX();
      // Query execution is done, add code to inform user
}

// the connection is closed - notify user

Notifications should be asynchronous to avoid blocking the database code you can implement them with events.

Answer 2

Are you looking to trap the StateChange event? Hope this will point you at the right direction.

    Dim csb = New NpgsqlConnectionStringBuilder(GetConnectionString(connectionName))
    csb.CommandTimeout = 0
    Using connection = New NpgsqlConnection(csb.ConnectionString)
        AddHandler connection.StateChange, AddressOf myHandler  ' <== This is where you specify the event Handler
        Using transaction = connection.BeginTransaction()
            ' Do your thing here.
            transaction.Commit()
        End Using
    End Using
End Sub


' This function will get called whenever the connection state changes.
Private Function myHandler(sender As Object, e As StateChangeEventArgs) As Object
    ' Do something here
End Function