Synopse Open Source

In our documentation, and in all our code source, we avoid using the VCL DB.pas related units, and all the associated RAD components.

This is by design, since our experiment encouraged us to "think ORM, forget anything about RAD (and even SQL in most cases)" in mORMot.
And it introduced some nice border-side effect to Delphi users, e.g. that even a "Delphi Starter Edition" is able to use mORMot, have access to SQLite3, MS SQL or Oracle or any other DB, add interface-based RESTful JSON services over it, just for free...

But in the real world, you may need to upgrade some existing application, get rid of the BDE, or add a SOA layer over an existing business intelligence.
And mORMot is able to serve you well in those scenarios.
That's why we just added a first attempt to expose SynDB results and mORMOt TSQLTableJSON content into a TDataSet.

The memory allocation model of the Delphi interface type uses some kind of Automatic Reference Counting (ARC). In order to avoid memory and resource leaks and potential random errors in the applications (aka the terrible EAccessViolation exception on customer side) when using interface, a SOA framework like mORMot has to offer so-called Weak pointers and Zeroing Weak pointers features.

Note that garbage collector based languages (like Java or C#) do not suffer from this problem, since the circular references are handled by their memory model: objects lifetime are maintained globally by the memory manager. Of course, it will increase memory use, slowdown the process due to additional actions during allocation and assignments (all objects and their references have to be maintained in internal lists), and may slow down the application when garbage collector enters in action. In order to avoid such issues when performance matters, experts tend to pre-allocate and re-use objects: this is one common limitation of this memory model, and why Delphi is still a good candidate (like unmanaged C or C++ - and also Objective C) when it deals with performance and stability.

It is pretty useful, in some cases, to retrieve a class instance from a given interface.
You should better use interfaces in your business logic, but having access to the underlying implementation is needed at lower level.

Beginning with Delphi 2010, you are able to use the as operator, e.g. via aObject := aInterface as TObject or aObject  := TObject(aInterface).
This operator use a special hidden interface GUID (ObjCastGUID) to retrieve the object instance, calling an enhanced version of TObject.GetInterface.

But if you want to maintain compatibility with older version of Delphi (as we want for mORMot to work with the beloved Delphi 6 or 7), you'll have to find a way.