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.

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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.

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Modeling: From Structured Data Representation to Problem Domain

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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.

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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.

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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.

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