CODEWITHSUNDEEP
iosobjective-ccore-datanspredicate
BBruce
BBruce

Reputation: 265

iOS Predicate Subquery not working

I am banging my head on this one... My app has the following coredata entities:

MenuItem ContentItem

MenuItems can have many ContentItems and each ContentItem can belong in many MenuItems, so I have a many to many relationship between the two.

The relationships are: MenuItem -->> ContentItem: menuContentItems

ContentItem -->> MenuItem: contentItemMenuItem

I am trying to use the MenuItem's title attribute for the predicate, so my selected MenuItem's title is used in the predicate.

When the user selects a MenuItem, I want to display the ContentItems related to that MenuItem.

To show the correct list of ContentItems, I tried a standard predicate like this:

[fetchedRequest setPredicate:[NSPredicate predicateWithFormat:@"ANY contentItemMenuItem.title = %@", selectedMenuItem.title]];

No luck. I get this error:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath contentMenuItem.title not found in entity <NSSQLEntity ContentItem id=2>'

I also tried a subquery like this:

[fetchedRequest setPredicate:[NSPredicate predicateWithFormat:@"SUBQUERY(MenuItem, m$, m.title =  %@)",selectedMenuItem.menuItemTitle]];

Also no luck. Error:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to parse the format string "SUBQUERY(MenuItem, m$, m.title =  %@)"'

There has to be a way for this to work.

Upvotes: 0

Views: 316

Answers (1)

Paul.s
Paul.s

Reputation: 38728

You should be able to just use

[selectedMenuItem valueForKey:@"menuContentItems"];

Out of curiosity if you ever needed to get that SUBQUERY working it would look like this

  This evaluates to a collection e.g. `contentItem.menuItems`
             |
             |              This is the predicate
             |                       |
             v                       V
SUBQUERY(menuItems, $menuItem, $menuItem.title == 'test').@count > 0
                       ^
                       |
       This is what each item will be referred as in the predicate

The subquery will return a collection of results so we then just ask if there are more than 0 items returned, if so then we had a match.

Upvotes: 4

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