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    <p>Firstly, I would check that the relationship is set from the other side by logging <code>self.session</code>. If that shows as null then you have no reciprocal relationship set in the model.</p> <p>I think that your fetch is poorly constructed. You are relying on the sort descriptor to provide the last used session but you only have a fetch limit of 1. You seem to think that the fetch will find all existing <code>Session</code> objects, sort them and then return the first one. However, sorts execute last so the fetch will find a single session object (because of the fetch limit) and will then apply the sort to that single object. This makes it likely that you will be dealing with a more or less random <code>Session</code> object. </p> <p>You probably don't need a fetch at all because you are only interested in the <code>Session</code> objects in a relationship with the <code>User</code> object which is <code>self</code>. If you already have the object in one side of a relationship, you don't need to fetch, you just need to walk the relationship. All you really need to do is:</p> <pre><code>if ([self.session count]==0){ //...create new session and set relationship }else{ //... find latest session } </code></pre> <p>I think your problem with this particular chunk of code is in the reporting. When you get a return value, you use the <code>self.user</code> notation but where you get a <code>null</code> return you use <code>valueForKey:</code>. </p> <p>While in theory both return the same value, they don't have to because they don't use the same mechanism to return the value. The self-dot notation calls an accessor method while <code>valueForKey:</code> may or may not depending on the specifics of a class' implementation. I would test if the <code>self.session</code> returns a value where <code>valueForKey:</code> does not. </p>
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    1. POWhy is Core Data losing one of my values?
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    1. COI have responded above. And that's very interesting about the application order of limit vs sort. I had expected the sort to apply first. Isn't the limit pretty much useless when it is picking unsorted records at random??
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    2. COSorting before limiting the fetch would defeat the purpose of the limiting the fetch. You limit a fetch so that you only have to hit the store so much at anyone time. If you sort first, you would have to process an arbitrary number of records and then return on a few. That would not be efficient. Sorts are really only for purposes of display i.e. they are a convenience. You can always sort a fetched array or objects yourself. Predicate, by contrast, have to evaluated against the store.
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    3. COYou really want a min/max predicate here instead of relying on a sort.
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