CODEWITHSUNDEEP
core-data
clx
clx

Reputation: 175

Core Data - fetch distinct records with all properties

considering I have core data objects stored like this:

|Name | ActionType | Content | Date      |
|-----|------------|---------|-----------|
|Abe  | Create     | "Hello" | 2014-07-01|
|Cat  | Create     | "Well"  | 2014-07-01|
|Abe  | Create     | "Hi"    | 2014-07-02|
|Bob  | Edit       | "Yo"    | 2014-07-03|
|Cat  | Delete     | "What"  | 2014-07-04|
|Abe  | Edit       | "Haha"  | 2014-07-05|

I would like to get the last action of each user, so the results would be

|Abe  | Edit       | "Haha"  | 2014-07-05|
|Cat  | Delete     | "What"  | 2014-07-04|
|Bob  | Edit       | "Yo"    | 2014-07-03|

Does anyone knows how to do that with a NSFetchRequest? So far from what I've gathered, if you want to use "group by", you can only retrieve the values in the group by cause (it will return "Abe, Cat, Bob" without the rest of the data in the core data object). Similar with "returnsDistinctResults", it will not return the whole object.

I have a feeling that core data is not equipped for that, any helps & hints would be appreciated!

Upvotes: 0

Views: 81

Answers (1)

quellish
quellish

Reputation: 21244

Core Data is an object graph, not a database. Core Data itself has no concept of uniqueness, it's up to you to implement that in your application. This is most typically done using the find or create pattern. This pattern helps you prevent duplicate objects from being stored.

That said, you CAN return distinct results from Core Data using the NSDictionaryResultType. This will not prevent duplicates from being stored, but can be used to return distinct results from a fetch. There is an example of this in the programming guide. You can give this request all properties for a given entity by working with the NSEntityDescription of the managed object you are fetching.

For getting the object with the "last" timestamp for each, you actually want to get the object with the maximum value for that key path. That can be done a number of ways - a subquery, key path operators, expressions, etc.

Upvotes: 1

Related Questions