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copied!<p>Yes.</p> <blockquote> <p>There is however one aspect which still leaves me puzzled: how to properly model to-many relationships, especially when the collection is to be publicly immutable, but privately mutable ….</p> </blockquote> <p>Easy: Declare the property as <code>readonly</code> in the header, then <a href="http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/Articles/ocProperties.html#//apple_ref/doc/uid/TP30001163-CH17-SW19" rel="nofollow noreferrer">redeclare it as <code>readwrite, copy</code> in a class extension</a> in the implementation file.</p> <blockquote> <p>I do understand how to implement the KVC accessor methods for to-many relationships (<code>countOf<Key></code>, <code>objectsIn<Key>AtIndex</code>, etc.) and this is the route I've been following so far.</p> </blockquote> <p>There are mutative ones, too. With these, you don't need to use <code>mutableArrayValueForKey:</code>; instead, you can use the mutative accessors directly. You'll still get KVO notifications, because KVO wraps those methods the first time something adds itself as an observer for the property.</p> <p>I have <a href="http://boredzo.org/blog/archives/2007-08-07/a-complete-raw-list-of-kvc-accessor-selector-formats" rel="nofollow noreferrer">a list of the accessor selector formats</a>, including the mutative accessors, on my blog.</p> <p>Edit:</p> <blockquote> <p>Even when I declare a to-many property as readonly, like in the example above, external code can still call <code>mutableArrayValueForKey:@"transactions"</code> on the model object and mutate the collection.</p> </blockquote> <p>This is a good reason to make it a habit to use the mutative accessors and avoid <code>mutableArrayValueForKey:</code>. You won't send mutation messages from outside the class if you get a compiler warning (no such [public] method) any time you try it.</p> <p>Despite the availability of <code>mutableArrayValueForKey:</code> and the risk that someone will use it, KVO-compliant properties <em>are</em> the way to go here.</p>

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