Re: Standalone prefetch without main query?

1.  Remember that EOEditingContexts do uniquing, meaning that if there's a 
'fault' for a particular StockItem, and then you fetch that StockItem on 
your own with a fetch spec, that 'fault' is now a real object and accessing 
it won't be a trip to the db.  That is, you don't need to run the query 
against the StockGroup to 'populate' it's relationship---you just need to 
fetch the StockItems in question.

I forgot this myself for a while and gave myself a lot of unneccesary work.

So, one option would be to construct a fetch spec to fetch all those 
StockItems you know you'll need. Some qualifier like "stockGroup = %@ OR 
stockGroup = %@ OR stockGroup =%@" etc.  Note that you can construct an 
EOQualifier of the form "relationship = EOEnterpriseObject", you don't 
actually need to deal with the primary/foreign keys.

2.  Batch faulting, as opposed to fetching, may also be of use to you here. 
See:
http://developer.apple.com/techpubs/webobjects/WebObjects_5/Topics/ProgrammingTopics.8.html

Actually, that documentation is kind of sketchy (and not updated for WO5), 
now that I look at it. 'Batch faulting' is kind of a misnomer for what I'm 
reccomending, which is specifically the EODatabaseContext method

batchFetchRelationship(EORelationship relationship, NSArray objects, 
EOEditingContext editingContext)

It does pretty much exactly what you want, although you inconveniently need 
to look up the actual EORelationship object, not just give it the name of 
the relationship. You could write a utility method that takes a String 
relationship name instead, and looks up the EORelationship (by taking a 
typical object from the NSArray and looking up it's EOEntity).


At 11:14 AM 10/30/2002 +0000, John Pollard wrote:
>An eof prefetch brain teaser,
>
>I have an object StockGroup that has a relationship stockItems(). I have a 
>number of StockGroup objects already in my editing context. I know I am 
>going to access all of the stockItems() arrays so I don't want a query 
>triggered for each one.
>
>The solution I have come up with is to write a fetch spec to fetch 
>StockGroups based on their primary keys and to prefetch the stockItems 
>relationship.
>
>That is not bad because it results in just two queries (the StockGroup 
>query and the StockItem prefetch query). However, in an ideal world I only 
>need the second (prefetch) query to execute because I already have the 
>StockGroups in memory.
>
>I am only running the query against the StockGroup entity because it is 
>the only way I know to populate the stockItems() of a number of 
>StockGroups in one go. Is there another way? Some way I can just run the 
>prefetch bit of the query which is the bit I need?
>
>Thanks
>John
>
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