Core Data - How can I get the max value from an entity attribute (Swift)

Question

Recipe

recipeID: Int
recipeName: String

I have an entity Recipe with an attribute recipeID. How can I get the max(recipeID) as an Int value in Swift?

I'm new in swift, please help me. Thanks in advance.

func fetchMaxID() {
    let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
    let fetchRequest = NSFetchRequest(entityName: "Recipe")

    fetchRequest.fetchLimit = 1
    let sortDescriptor = NSSortDescriptor(key: "recipeID", ascending: false)
    fetchRequest.sortDescriptors = [sortDescriptor]
    do {
        let maxID = try [managedObjectContext?.executeFetchRequest(fetchRequest)].first
        print(maxID)
    } catch _ {

    }
}

Possible duplicate of [Core Data - How to fetch an entity with max value property](https://stackoverflow.com/questions/10398019/core-data-how-to-fetch-an-entity-with-max-value-property) — Abizern, Aug 27 '17 at 12:12

jarora · Answer 1 · 2017-08-27T12:10:02.490

The way that Apple recommends and is the fastest is using NSExpressions. moc is a NSManagedObjectContext.

private func getLastContactSyncTimestamp() -> Int64? {

    let request: NSFetchRequest<NSFetchRequestResult> = NSFetchRequest()
    request.entity = NSEntityDescription.entity(forEntityName: "Contact", in: self.moc)
    request.resultType = NSFetchRequestResultType.dictionaryResultType

    let keypathExpression = NSExpression(forKeyPath: "timestamp")
    let maxExpression = NSExpression(forFunction: "max:", arguments: [keypathExpression])

    let key = "maxTimestamp"

    let expressionDescription = NSExpressionDescription()
    expressionDescription.name = key
    expressionDescription.expression = maxExpression
    expressionDescription.expressionResultType = .integer64AttributeType

    request.propertiesToFetch = [expressionDescription]

    var maxTimestamp: Int64? = nil

    do {

        if let result = try self.moc.fetch(request) as? [[String: Int64]], let dict = result.first {
           maxTimestamp = dict[key]
        }

    } catch {
        assertionFailure("Failed to fetch max timestamp with error = \(error)")
        return nil
    }

    return maxTimestamp
}

For info, this is a duplicate answer of [this](https://stackoverflow.com/a/42645137/254035) — wardw, Aug 27 '17 at 11:54
Good that you pointed this out but one of the questions asked for a swift specific solution and other asked for an objective-c one. So, I am not too sure if it counts as a duplicate question. Again, I'm not sure about what's the right call here. — jarora, Aug 27 '17 at 12:12
The correct call is to flag the question as a duplicate and point the questioner to the answer available there. — Abizern, Aug 27 '17 at 12:13

Mochi · Answer 2 · 2016-08-23T14:49:56.313

Learning from Ray Wenderlich's Core Data Tutorial

https://www.raywenderlich.com/115695/getting-started-with-core-data-tutorial/

func fetchMaxRecipe() {
    let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
    let fetchRequest = NSFetchRequest(entityName: "Recipe")

    fetchRequest.fetchLimit = 1
    let sortDescriptor = NSSortDescriptor(key: "recipeID", ascending: false)
    fetchRequest.sortDescriptors = [sortDescriptor]
    do {
        let recipes = try context.executeFetchRequest(fetchRequest) as! [Recipe]
        let max = recipes.first
        print(max?.valueForKey("recipeID") as! Int)
    } catch _ {

    }
}

Hope this helps =).

@Michael You're welcome. I actually learned from your code thats strong casting fetch request as [Recipe] leads to shorter and cleaner code. Thanks. Just edited it. — Mochi, Aug 23 '16 at 14:53

score 2 · Answer 3 · answered Aug 23 '16 at 14:36

func fetchMaxID() {
    let context = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
    let fetchRequest = NSFetchRequest(entityName: "Recipe")

    fetchRequest.fetchLimit = 1
    let sortDescriptor = NSSortDescriptor(key: "recipeID", ascending: false)
    fetchRequest.sortDescriptors = [sortDescriptor]
    do {
        let results = try context.executeFetchRequest(fetchRequest) as! [Recipe]
        if (results.count > 0) {
            for result in results {
                print(result.recipeID!)
            }
        } else {
            print("No Recipe")
        }
    } catch let error as NSError {
        // failure
        print("Fetch failed: \(error.localizedDescription)")
    }

}

This works also!

score 0 · Answer 4 · answered Sep 19 '18 at 23:05

To check the max of an entity attribute you can simply use:

func findMaxRecipeID() -> Int {
    let maxRecipeID = recipe?.value(forKeyPath: "recipe.@max.recipeID") as! Int
    return maxRecipeID
}

You can use this to @sum, @max, @min, @count - saves quite a few lines of code.

Core Data - How can I get the max value from an entity attribute (Swift)

Recipe

4 Answers4