CODEWITHSUNDEEP
iosuitableviewcore-data
rattletrap99
rattletrap99

Reputation: 1479

iOS retrieving and ordering Core Data entities with relationships

I recently asked this question about how best to retrieve and display in a tableview the titles my FRC is using for section headers.

Following a line of research suggested by @Mike Pollard in the second answer to my question, I ran across this question and was immediately struck by the similarity to my situation, and by the 4th answer, posted by @aroth.

Aroth's approach certainly appears sound, and I've created a new Category entity. Specifically, Category has a to-many relationship with Item, and Item has a to-one relationship with Category. However I'm having trouble understanding one aspect implicit in his proposed solution, and, more fundamentally, in this relationship:

In my case, both Category(s) and Item(s)--"Item" is called "ListActivity" in my case, but "Item" will do for illustration purposes-- will be named via two corresponding user input fields, which seems like it could result in multiple entries of the same name in the Category list.

My question:

How can I ensure that when I fetch a list of Categories that I get a singular instance of each category, i.e., one category per row in the tableview, with no repeats? Will Core Data automatically assign each new incoming Item to a singular instance of the appropriate Category via the relationship? Or will it somehow test for and winnow the list down to one entry per Category name upon receiving the fetch request? Or must the filtering be done with a predicate in the fetch request?

Thanks!

Upvotes: 0

Views: 58

Answers (1)

Wain
Wain

Reputation: 119021

Core Data will do what you tell it to. This sounds like an issue related to you creating content in your data store rather than an issue with the FRC and table view. It's your responsibility to search for and reuse existing objects rather than creating duplicates and adding them to the store - indeed, only you (your code) knows what constitutes a duplicate.

So, basically, as you create new items, use a fetch request and predicate to find the suitable existing category (or suggest categories based on partially entered names). Then, either connect to the existing category or create a new one.

Upvotes: 1

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