dorm, “The Delphi ORM” and Spring for Delphi Framework

"The Delphi ORM", Spring4D, dorm 5 Comments »

Great news for all the dorm and Spring4D users!

As you probably know, finally has been announced the official Spring framework for Delphi.

There is a lot of good technology in Spring4D!

So, I’m glad to announce that in a future version (hopefully, the next one) dorm, “The Delphi ORM” will use Spring4D and will become the ORM part of Spring4D.

So, dorm will be part of the Spring4D framework.

More info to come, so stay tuned.

#1 “dorm, the Delphi ORM” bullettin

"The Delphi ORM" 1 Comment »

This is the first post regarding a fast update on the last changes to the dorm project in terms of management and code.

  • Welcome to 2 new contributors: mrbar2000 and magnomp (this is the full list http://code.google.com/p/delphi-orm/people/list)
  • Added a PersistentStrategy for SQLite.
  • New Google Group related to dorm. Post your questions, comments and request here!
  • Added support for Generics Collections. No more needs of TdormCollection. You classes are completely decoupled from the framework.
  • A brand new mapping strategy is under development. There will be “3 levels” of mapping: Config File, RTTI Attributes and “Conventions Over Configuration” (CoC) (do you wanna check the code in dev branch? Click here)
  • Added more unittests
  • Roadmap updated
  • Initial support for MS SQLServer in a development branch (Thanks to Claudio Regonat)
There are plenty of new features still to come. Stay tuned!

Duck Typing in Delphi

"The Delphi ORM", Delphi XE2, Programming, Uncategorized 9 Comments »

During a new dorm feature development, I’m faced a nice problem:

I want to have a generic access to a “kind” of list

Let’s say:

  1. procedure DoSomething(Obj: TMyListType);
  2. begin
  3. end;

But, I want to have that generic access without a Layer Supertype object, because I need to be able to use objects from other libraries or 3rd party. In this case traditional polimorphism is not usable, so I’ve opted for an interface…

  1. procedure DoSomething(MyIntf: IMyListInterface);
  2. begin
  3. end;

Cool, but I want to have that access without any change to that object. So implement an interface is not a viable solution. This is particulary true because the generics data structure in Delphi do not implement an interface. Will be nice to have a fully interfaced list and dictionaries in a future Delphi version.

So, how I could implement a generic access to a generic list?

  1. procedure DoSomething(MySomething: ???);
  2. begin
  3. end;

However, operations on that list are few and well known, so I’ve opted for a “DuckTyping“.

Introducing The Duck

Introducing The Duck

The name of the concept refers to the duck test, attributed to James Whitcomb Riley, which may be phrased as follows:

“When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck.”

So, in my case, I’ve created an Adapter object wich adapts the external interface (few, well know operations) to the “duck” inside it.

The adapter is useful because I can use the compiler checking that the RAW RTTI access doesn’t allow.

Write an “RTTI adapter” using the new Delphi RTTI, is very simple. This is the code of the class TDuckTypedList that allow to use any object as a “list”. How I can define that the object is actually a list?

The criteria is:

If the object has
- An “Add” method with one parameter of type TObject (or descendant);
- A “Count” property;
- A “GetItem” method that have an integer parameter and return an object;
- A “Clear” method;
then, that object is a list.

So I can write the following:

  1. DuckObject := TDuckTypedList.Create(Coll);  //the adapter
  2. for x := 0 to DuckObject.Count - 1 do
  3.   DoSomething(DuckObject.GetItem(x));

I’ve done some speed tests comparing this way to the classic static way, and the speed is almost the same because the RTTI lookup is cached in the constructor of the adapter. So, so far so good.

This solution is already in use inside the dorm code in a feature branch.

Full code is available in the dorm SVN

Any comments?

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