Is this a problem typically solved with IOC?
- by Dirk
My current application allows users to define custom web forms through a set of admin screens. it's essentially an EAV type application. As such, I can't hard code HTML or ASP.NET markup to render a given page. Instead, the UI requests an instance of a Form object from the service layer, which in turn constructs one using a several RDMBS tables. Form contains the kind of classes you would expect to see in such a context: Form= IEnumerable<FormSections>=IEnumerable<FormFields>
Here's what the service layer looks like:
public class MyFormService: IFormService{
public Form OpenForm(int formId){
//construct and return a concrete implementation of Form
}
}
Everything works splendidly (for a while). The UI is none the wiser about what sections/fields exist in a given form: It happily renders the Form object it receives into a functional ASP.NET page.
A few weeks later, I get a new requirement from the business: When viewing a non-editable (i.e. read-only) versions of a form, certain field values should be merged together and other contrived/calculated fields should are added. No problem I say. Simply amend my service class so that its methods are more explicit:
public class MyFormService: IFormService{
public Form OpenFormForEditing(int formId){
//construct and return a concrete implementation of Form
}
public Form OpenFormForViewing(int formId){
//construct and a concrete implementation of Form
//apply additional transformations to the form
}
}
Again everything works great and balance has been restored to the force. The UI continues to be agnostic as to what is in the Form, and our separation of concerns is achieved. Only a few short weeks later, however, the business puts out a new requirement: in certain scenarios, we should apply only some of the form transformations I referenced above.
At this point, it feels like the "explicit method" approach has reached a dead end, unless I want to end up with an explosion of methods (OpenFormViewingScenario1, OpenFormViewingScenario2, etc). Instead, I introduce another level of indirection:
public interface IFormViewCreator{
void CreateView(Form form);
}
public class MyFormService: IFormService{
public Form OpenFormForEditing(int formId){
//construct and return a concrete implementation of Form
}
public Form OpenFormForViewing(int formId, IFormViewCreator formViewCreator){
//construct a concrete implementation of Form
//apply transformations to the dynamic field list
return formViewCreator.CreateView(form);
}
}
On the surface, this seems like acceptable approach and yet there is a certain smell. Namely, the UI, which had been living in ignorant bliss about the implementation details of OpenFormForViewing, must possess knowledge of and create an instance of IFormViewCreator.
My questions are twofold: Is there a
better way to achieve the
composability I'm after? (perhaps by
using an IoC container or a home
rolled factory to create the
concrete IFormViewCreator)?
Did I fundamentally screw up the
abstraction here?
