Logging every data change with Entity Framework

Question

There is a need from a customer to log every data change to a logging table with the actual user who made the modification. The application is using one SQL user to access t

Answer 1

Simply force an execution of the SET CONTEXT_INFO by using your DbContext or ObjectContext:

...
FileMoverContext context = new FileMoverContext();
context.SetSessionContextInfo(Environment.UserName);
...
context.SaveChanges();

FileMoverContext inherits from DbContext and has a SetSessionContextInfo method. Here is what my SetSessionContextInfo(...) looks like:

public bool SetSessionContextInfo(string infoValue)
{
   try
   {
      if (infoValue == null)
         throw new ArgumentNullException("infoValue");

      string rawQuery =
                   @"DECLARE @temp varbinary(128)
                     SET @temp = CONVERT(varbinary(128), '";

      rawQuery = rawQuery + infoValue + @"');
                    SET CONTEXT_INFO @temp";
      this.Database.ExecuteSqlCommand(rawQuery);

      return true;
   }
   catch (Exception e)
   {
      return false;
   }
}

Now you just set up a database trigger which can access the CONTEXT_INFO() and set a database field using it.

Answer 2

Thanks for pointing me in the right direction. However, in my case, I also need to set the context info when doing select statements, because I am querying views that use the context info to control row-level security by user.

I found it easiest to attach to the StateChanged event of the connection and just watch for the change from not-open to open. Then I call the proc that sets context and it works every time, even if EF decides to reset the connection.

private int _contextUserId;

public void SomeMethod()
{
    var db = new MyEntities();
    db.Connection.StateChange += this.Connection_StateChange;
    this._contextUserId = theCurrentUserId;

    // whatever else you want to do
}

private void Connection_StateChange(object sender, StateChangeEventArgs e)
{
    // only do this when we first open the connection
    if (e.OriginalState == ConnectionState.Open ||
        e.CurrentState != ConnectionState.Open)
        return;

    // use the existing open connection to set the context info
    var connection = ((EntityConnection) sender).StoreConnection;
    var command = connection.CreateCommand();
    command.CommandText = "proc_ContextInfoSet";
    command.CommandType = CommandType.StoredProcedure;
    command.Parameters.Add(new SqlParameter("ContextUserID", this._contextUserId));
    command.ExecuteNonQuery();
}