CODEWITHSUNDEEP
iosswiftuitableviewcore-data
David Robertson
David Robertson

Reputation: 1581

Core data skips fetch function Swift

I've been implementing the core data framework lately and every step of the implementation had a hidden issue behind. Here comes the issue i'm not really sure how to solve.
So far i've implemented a save and fetch functions for my tableview.
First of all fetch was returning data faults, so i've implemented 

fetchRequest.returnsObjectsAsFaults = false

now the data was fed and shown in the tableview, but it had a massive amount of duplicates and was in chaotic order, so i've added

fetchRequest.returnsDistinctResults = true

but this didn't work so after googling i've implemented the following one liner

fetchRequest.resultType = NSFetchRequestResultType.DictionaryResultType

as a final result the fetch function doesn't run at all. debugger simply skips the action and the app returns an empty tableview.

Here is my code. Looking forward to any suggestions:

func fetchItems() {

    // get the managed object context

    let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedObjectContext = appDelegate.managedObjectContext!

    // create fetch requests

    let fetchRequest = NSFetchRequest(entityName:"Entities")

    fetchRequest.returnsObjectsAsFaults = false
    fetchRequest.returnsDistinctResults = true
    fetchRequest.resultType = NSFetchRequestResultType.DictionaryResultType
    var fetchedResults : [NSManagedObject]?
    do {
        fetchedResults = try managedObjectContext.executeFetchRequest(fetchRequest) as? [NSManagedObject]
    }
    catch {
        print("Could not fetch \(error)")
    }

    if let results = fetchedResults {
        someOtherArray = [results]
    }
}

Upvotes: 0

Views: 364

Answers (1)

pbasdf
pbasdf

Reputation: 21536

I doubt very much that you want or need these lines:

fetchRequest.returnsObjectsAsFaults = false
fetchRequest.returnsDistinctResults = true
fetchRequest.resultType = NSFetchRequestResultType.DictionaryResultType

The first is primarily a performance optimisation. "Faults" are generally speaking not a cause for concern - CoreData is saving memory by not populating the property values for all the objects returned by the fetch. But it will do so automatically for each object as soon as you try to access any of its properties. So that line is fine, but unnecessary.

Regarding the duplicate data, you shouldn't be using returnsDistinctResults to suppress them, you should avoid creating them.

The final line is the cause of your empty table view. Because you specify DictionaryResultType, the array returned by the fetch is an array of dictionaries. But with this line:

    fetchedResults = try managedObjectContext.executeFetchRequest(fetchRequest) as? [NSManagedObject]

you are then trying to cast that array as an array of NSManagedObjects. That cast fails, and consequently fetchedResults is nil, and consequently someOtherArray is not set.

Regarding the chaotic order, you should use a sort descriptor (see the NSSortDescriptor documentation) to sort the results how you would like.

Finally, as in your other question, you are setting someOtherArray to be [results], which is an array containing the results array. I suspect you actually want:

 someOtherArray = results

Upvotes: 1

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