http://www.gekko-software.nl/DotNet/Art09.htm Creating a Delphi Component for a .net XML dataset Wrapping up the DNdataset The DNdataset, described in detail in another paper, can wrap up a XMLdataset as returned by a .NET webservice. The objects of this class need the tHTTPrio component to get to the webservice supplying the dataset. I will build a component which descends from the tHHTPrio component, manages a DNdataSetobject and publishes all data relevant to other Delphi components. The component invokes the webservice via its public Get and Update method. The component internally keeps an invocation state to guide the process type tDataRequestState = (RequestLoad, RequestSave, RequestNone); Get Calling the Get method will set the component's state and fire the OnRequestInvocation event. In the assigned eventhandler the user of the component is requested to invoke the method returning the XML dataset. To conclude the state is set back to Request None. procedure TGekkoDotNetDataSet.Get; begin fDataRequestState:= RequestLoad; if Assigned(fOnRequestGetInvocation) then fOnRequestGetInvocation(self); fDataRequestState:= RequestNone; end; Intercepting the response from a webservice The responses from the webservice can be caught in the virtual DoAfterExecute method of the tRio class. The response contains all the XML the DNdataset needs to fill its values. I override the method, read the response to construct the object, and pass the response on to the inherited DoAfterExecute. procedure TGekkoDotNetDataSet.DoAfterExecute(const MethodName: string; Response: TStream); begin case fDataRequestState of RequestLoad : begin fDNdataset:= tDNdataSet.Create(self); fDNdataset.CreateFromStream(Response); end; end; inherited DoAfterExecute(MethodName, Response); end; Update Calling the Update method sets, after a check if there are any updates available, the state to RequestSave and it will fire the OnRequestUpdateInvocation event. The user of the component is requested to invoke the update method. The signature of the update method is fixed. It has one parameter, an xmlDocument typed by a schema. The component will provide the actual contents of this document. procedure TGekkoDotNetDataSet.Update; begin if fDNdataSet.IsUpdated then begin fDataRequestState:= RequestSave; if Assigned(fOnRequestUpdateInvocation) then fOnRequestUpdateInvocation(self); fDataRequestState:= RequestNone; end; end; Intercepting the request to a webservice. The request to the webservice can be intercepted in the virtual DoBeforeExecute method of tRio. The component does override this method. This takes some extra attention as Borland decided to change the signature of this method when moving from D6 to D7. In D6 the request is a string and the Response is a stream. The request also is a var parameter in D6, which implies that the method can effectively change the request. Which is what the component wants to do, it will substitute the parameter with the UpdateXML document created by the DNdataSet object. {$IFDEF VER140} { Delphi 6 } procedure TGekkoDotNetDataSet.DoBeforeExecute(const MethodName: string; var Request: InvString); begin case fDataRequestState of RequestLoad : FreeAndNil(fDNdataSet); RequestSave : Request := AnsiReplaceStr(Request, '<' fParamName '/>', fDNdataSet.UpdateXML(fParamName)); end; inherited DoBeforeExecute(MethodName, Request); end; {$ENDIF} After which the inherited DoBeforeExecute is called. There are many benefits in working with the request as a stream. Borland chose only to change the DoBeforeEvent method, not the signature of the OnBeforeExecute event of tHTTPrio componenet. To quote rio.pas : { Ideally we would change the signature of this event to take a Stream. The change to stream was necessary for attachment and encoding support. And it makes the event consistent.... However, for the sake of backward compatibility.... } For the sake of backward compatibility the signature of the associated event handler, OnBeforeExecute did not change. The implementation of the method changed, the fact that the OnbeforeExcute signature had a var parameter is neglected in D7. { NOTE: We ignore the var WideString passed in... ???? } Which rises a version problem. I will have to create a separate override of this method for D6 and D7. Using compiler directives the right version of the method will be used when the component is build. {$IFDEF VER150} {Delphi 7} procedure TGekkoDotNetDataSet.DoBeforeExecute(const MethodName: string; Request: TStream); var RequestAsString : string; StrStrm : TStringStream; begin case fDataRequestState of RequestLoad : FreeAndNil(fDNdataSet); RequestSave : begin StrStrm := TStringStream.Create(''); try StrStrm.CopyFrom(Request, 0); Request.Position := 0; RequestAsString := AnsiReplaceStr(StrStrm.DataString, '<' fParamName '/>', fDNdataSet.UpdateXML(fParamName)); StrStrm.Position:= 0; StrStrm.WriteString(RequestAsString); Request.Position:= 0; Request.CopyFrom(StrStrm, 0); finally StrStrm.Free; end; end; end; inherited DoBeforeExecute(MethodName, Request); end; {$ENDIF} This implementation uses a temporary tStringStream. The request is copied into this stream after which the string representation, in DataString, can be accessed. In this string the parameter is substituted with the xmlDocument generated by the DNdataSet. The resulting string is written back to the string-stream. I start writing at position 0 so the new request is copied over the original request. I make the assumption that the request always grows in size. When the request is ready it is copied back to the original request stream. Again I overwrite the original request. The inherited DoBeforeExecute will receive the changed request. To sum this up protected { Protected declarations } {$IFDEF VER140} { Delphi 6 } procedure DoBeforeExecute(const MethodName: string; var Request: InvString); override; {$ENDIF} {$IFDEF VER150} {Delphi 7} procedure DoBeforeExecute(const MethodName: string; Request: TStream); override; {$ENDIF} procedure DoAfterExecute(const MethodName: string; Response: TStream); override; The implementations are also enclosed in IFDEF directives. Your compiler will select the right source. Thanks for drBob for helping me getting this to work, thanks to Alex Kovalev for making clear to me why my previous code didn't work in D7. I have to admit I got stuck in 6.02 (pro). Installing the component The component, the dotnetdataset class and all other helper classes are in the GekkoDotNet pacakage. This package can be opened in Delphi to build and install it. The component will install itself on the webservices page. In the next paper I will show how to use the GekkoDotNetDataSet component. What's next ? Using the component. Download the code. Inside the tDNdataset class. Data in .NET. .NET from a Delphi perspective Introducing .NET Comparing features of C#/Delphi and .NET/VCL Where does your Delphi knowledge fit in ? XML from a Delphi perpesctive Data in .NET, it's all about XML. An object oriented introduction to XML serialization and ADO.NET (sdgn) Data in .NET. Similarities and dissimilarities between the Delphi and .NET data classes. Working with .NET data in Delphi. Creating a Delphi Component wrapper for a .NET XML dataset. Inside the tDNdataset class. ASP.NET architecture Users, Sessions, Applications and Queues: Peaking the Architecture of an ASP.NET Application (dnj) ASP.NET webforms The datagrid revisited:Editing a live database in template columns Working with the datagrid component. (dnj) Taking Full Control: Build Your Own Reusable Datalist with VS.NET. Creating a custom datalist component. (dnj) User controls and other useful things. Building a real-world web applications (dnj) ASP.NET web services Building RADical Web Services with VS.NET. style="COLOR: black; font-style:normal; font-variant:normal; font-size:16px; font-family:Arial, Helvetica, sans-serif">Use an An XML web service to interface to a database. (dnj) Passing data in and out of web services using (typed) xml (-datasets). The Message is the Medium - Invoking a XML Web Service (dnj) Building a real-life web-experience : Don´t trip over the threads (dnj) COM interop in .NET Using automation in C# An introduction to using connectable automation objects in C#. Using automation (ActiveX/COM) objects in ASP.NET. dnj Building an automation server using C# Building automation servers in C# using the Gekko class library. Demo application A C# automation client and a C# automation server. The full story A big story which starts from scratch and ends with a full C# connectable COM server being used by MS-Word. Covers a lot of details of object oriented programming in .NET. Miscellaneous Creating a .net library Dynamic events on an ASP.NET Page. Working with eventhandlers in asp.net. (dnj) Threading Use a multithreaded Windows form to investigate threads in .NET. Building a Windows service to check email (sdgn) Smart apps voor smart devices met VS.NET 2003 (In Dutch !) (sdgn) The source of all evil, over de variabelen in je code. (In Dutch !) (sdgn) Learning .NET (Book reviews) A programmers' introduction to C# by Eric Gunnerson. An excellent jumpstart on programming C# which keeps its value as a reference guide. Inside C# by Tom Archer. A very good book to learn the C# programming language which does include a lot of technical background. If you want to know more about the internals of the framework read Applied Microsoft .NET Framework Programming by Jeffrey Richter. To understand how ASP.NET works and how you can build on this framework read Developing Microsoft ASP.NET server controls and components XML is everywhere in .NET. Applied XML programming for Microsoft .NET covers covers a lot of aspects of using XML to build real-life applications, .net style. For a very thorough coverage of XML you should read XML for ASP.NET developers. DNJ : This article is a on the site of the dotnetjunkies as a part of my contributions to their tutorials. SDGN : This article is in Dutch and on the site of the SDGN. Other stories