| Hello,
I have a WODisplayGroup displayGroup containing a collection of EOs. The entity is registered as a taggable entity, and its tag entity is "TemplateTag", a subclass of ERTag. I want to find the set of all TemplateTags that are currently applied to any object in displayGroup.allObjects()—that is, if I called tags() on each object in allObjects(), what would be the union of all the results (a subset of _all_ TemplateTags)? And that's literally how I'm finding them at the moment: by looping over each EO, calling tags(), and adding the result to an NSMutableSet.
This approach seems slow, and, indeed, is resulting in a lot of hits to the database. I've tried calling setPrefetchingRelationshipKeyPaths() on the WODisplayGroup's EOFetchSpecification in a couple of ways:
* using the keyPath "tags"—this lead ERProfiling.framework to claim a reduction in SQL statements to an acceptable level, but this wasn't reflected in logging out the actual SQL. * attempting to unroll that flattened relationship by using the internal names created for the intermediate relationships—this didn't seem to work at all.
I also tried ERXBatchFetchUtilities.batchFetch() on displayGroup.allObjects() using both of those key paths. The first made no difference (to the SQL output) and the second failed with an exception. (In all cases, the majority of the SQL statements were SELECTs from the join table.)
I have two questions:
1. Should I expect to be able to pre-fetch/batch-fetch ERTags like this at all?
2. If not, or in any case, can anyone suggest a better method to solve the original problem? (That is, how do I find the subset of all tags being those currently applied to a set of taggable EOs?)
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