"Object Aware" GUI Controls

Question

I have some business objects written in Delphi with a custom scheme of database persistence which is finally working for my needs. Ok, great. Now it's time for GUI implementations. And here begins the problems.

How to bind my object to the GUI properly?

I cannot use Data Aware controls since I isolated all data access components into the ORM layer, so I start to write some "Object Aware" controls using the RTTI unit (I'm working with Delphi 2010), but I have the feeling I'm going the wrong way...

Some ideas on how to resolve this using only the VCL controls?

Answer 1

You have several patterns for linking ORM with User Interface.

See for instance the Model GUI Mediator pattern. In short, you write an observer which will reflect the ORM content into the UI components, and vice versa. This has been implemented for instance in the tiOpf framework for Delphi (this link has videos).

Another approach is to map your data at runtime: you design your form just like usual, then you fill the content in the OnShow event, then the "Save" or "OK" button will validate then save the content into the ORM record. This is what is done in the main Sample application of our framework. Easy to code in this simple sample, but could lead into spaghetti code if you have a lot of fields and validation to operate.

The last approach is to let your ORM creates the form.

In our framework, you can define some UI properties about each table, in a dedicated structure. Then a single unit will create a form with all editable fields of your ORM object. Links to other records will be displayed as a combo box, booleans as checkboxes, sets as radioboxes, and so on. Then the filtering (e.g. trim a text field from spaces on left or right side) and the validation (e.g. ensure that a field value is unique or a valid IP address) is handled not in the UI part, but in the business logic itself, i.e. the ORM.

IMHO it's mandatory to keep a true multi-tier architecture. That is, the UI has to rely mostly on the business logic. For instance, data validation must be part of the ORM, not of the UI. For instance, if you decide to add a web client to your Delphi client application, you won't have to code the validation another time: it will be common to both clients, separated from the UI implementation details.