Building a Rich Domain In Iterations
I’m currently revising code from 3 years ago. The result is a replica of the old stuff – updating isn’t worth the effort, it’s written in Swift 3 and the code base is small, so I rewrite it and copy useful parts over. The public interface already differs from what I wrote 3 years ago. In the first step, I translated the old code but took what was there. For example, back then I had a DateRange type. Swift Ranges were less powerful back then, so I added a couple of convenient methods that I can now replace with the standard library protocols instead. So I demoted the type to typealias DateRange = Range<Date>. I also had a Date type (this was before NSDate dropped the “NS”) that I renamed to NormalizedDate. In the domain I work on, a date isn’t a date-time-combination, but just the year, month, and day. Confusingly, this type was a mere wrapper for NSDate that dropped the time information for quick comparisons.
Core Data is Invasive. You Can Hide It, Or You Can Embrace It
Found this nice post about using Swift protocols to expose read-only properties of Core Data managed objects so you don’t couple your whole app to Core Data. Using Swift protocols in Core Data NSManagedObjects is a great way to limit the visibility of properties and methods. In my 1st book on Mac app development I talked about this, too, and this is a lot easier to handle than a custom layer of structs that you have to map to NSManagedObject and back again. Core Data is designed to be invasive and convenient. It’s not designed to be used as a simple object-relational mapper.
Modeling: From Structured Data Representation to Problem Domain
Recently, I was discussing adding a feature to an application which is about event creation and booking. The project manager has a strong database background and works on the schema himself. The schema is also his go-to tool to express changes in the features. But thinking about the real Domain in terms of objects revealed much, much more.
Revisiting the Core Data + Domain Model Architecture
It happens that just yesterday I read about architecture smells in code. Among the examples was “subclasses don’t redefine methods”. In my post about Core Data and expressive domains earlier this week, I did just that: create a Egg subclass of CoreDataEgg to inherit CoreDataEgg’s behavior. That’s not what abstraction to superclasses is meant to do.
Expressive Domain Model, Core Data, and You
I’ve written a whole book on the topic of architecting a Mac app using Core Data. Today I found an approach which doesn’t add lots of overhead and which also doesn’t clutter everything everywhere. It’s pretty simple and involves Swift.
How to Create Flexible Components with Two Levels of Service Objects
Again I was reminded about the value of service objects to encapsulate sequences in two places: the Domain, where business rules are kept, and in client code, where database management and transactions play a role. This distinction helps create clean code and deliver flexible components. I am building a feature for the Word Counter in a separate “library” project until everything runs smoothly. Then I’ll integrate the code into the main application. Since I consider this to be some kind of library, I thought I wouldn’t need many service objects, but I was wrong.