Cannot cast generic 'Group' to 'NoMDEntriesGroup' about quickfixn HOT 15 CLOSED

Mail list thread:
http://lists.quickfixn.com/pipermail/quickfixn-quickfixn.com/2012q2/000124.html

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Has anyone looked at how Java does it?

from quickfixn.

A bit heavy handed, but would this work?

public void OnMessage(QuickFix.FIX42.MarketDataIncrementalRefresh message, SessionID sessionID)
{
    MDReqID mdReqID = message.MDReqID;

    int count = message.GetInt(Tags.NoMDEntries);
    var list = new List<QuickFix.Group>();
    for (int grpIndex = 1; grpIndex <= count; grpIndex++)
    {
        list.Add(message.GetGroup(grpIndex, Tags.NoMDEntries));        
    }

    foreach (var noMDEntriesGroup in list.OfType<QuickFix.FIX42.MarketDataIncrementalRefresh.NoMDEntriesGroup>())
    {
      // code omitted here
    }
}

If you're expecting them to all be NoMDEntriesGroup you might replace OfType with Cast.

from quickfixn.

Sorry I missed the part where you already tried the explicit cast. The above code probably won't be of any use.

from quickfixn.

Unfortunately, bigger hammers aren't the solution here. I've tried :).

So as far as a solution in code, what does everyone else think is the best method?

I'm a bit pressed for time but am willing to do some work on this. It'll make my life easier in the long run so my boss shouldn't mind.

from quickfixn.

We'd really like to maintain some semblance of similarity between QF/n and QF for C++/Java.

I'd really like to see how QF/J handles this. They might have a design we can steal. I'll have a look later if I can find the time.

from quickfixn.

I had the same problem with a MarketDataSnapshotFullRefresh.

A workaround was :

       QuickFix.Group mdGroup;

       for(int i = 1; i < message.GetInt(Tags.NoMDEntries);i++)
       {
           mdGroup = message.GetGroup(i, Tags.NoMDEntries);

           Console.WriteLine(mdGroup.GetString(Tags.MDEntryPx));
           Console.WriteLine(mdGroup.GetString(Tags.MDEntrySize));
       }

Hope this help !

S

from quickfixn.

That's how I ended up having to do it. Thanks Steven.

This is still a bug, so how should we go about fixing it? I don't mind doing some of the work, but I wouldn't want to attempt anything without guidance. I'm new to contributing to open source projects.

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Notes on methods of other QF versions:

QF: msg.getGroup(1,group_object) (this is a member of Message, not FieldMap)
QF/j: msg.getGroup(1,group_object) and group_object=msg.getGroup(1,tag_int) (each are from FieldMap)
QF/n: group_object = msg.GetGroup(1, tag_int)

Java: http://quickfixj.org/quickfixj/usermanual/1.5.1/usage/repeating_groups.html
C++: http://www.quickfixengine.org/quickfix/doc/html/repeating_groups.html

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Unit tests: https://github.com/gbirchmeier/quickfixn/tree/56_group

from quickfixn.

I see the root cause now. When Message::FromString() creates a Message object from a string, it constructs Group objects instead the type-specific subclasses of Group. Therefore, the objects retrieved by GetGroup() are also Group objects. You can't cast a base class to a subclass if it was never a subclass-type object in the first place.

So I need to see if we have some kind of Group factory to create the typed Group objects. If we don't, then I guess I need to generate one.

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Each of the following classes implements IMessageFactory that has a method called 'Create' that returns a Typed Group object based on the arguments passed in, it has the following signiture:
public Group Create(string beginString, string msgType, int correspondingFieldID)

The classes are:
QuickFix.FIX40.MessageFactory();
QuickFix.FIX41.MessageFactory();
QuickFix.FIX42.MessageFactory();
QuickFix.FIX43.MessageFactory();
QuickFix.FIX44.MessageFactory();

from quickfixn.

Thanks, Nick. I figured it was in there somewhere, but couldn't remember where. With this, I will probably be able to knock this out this week.

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I think I solved it on my branch. Will integrate tomorrow.
https://github.com/gbirchmeier/quickfixn/tree/56_group

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Damn, still failing AT 14i in the FIX50x sets.

Note to self:
cd AcceptanceTest
runat.bat release 5006 definitions\server\fix50\14i_RepeatingGroupCountNotEqual.def cfg\at_50.cfg
runat.bat release 5007 definitions\server\fix50sp1\14i_RepeatingGroupCountNotEqual.def cfg\at_50_sp1.cfg
runat.bat release 5008 definitions\server\fix50sp2\14i_RepeatingGroupCountNotEqual.def cfg\at_50_sp2.cfg

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