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hmm, I must be missing something.
let's take a simple department, employee example, in which I would like to find the sum of employee computers. The following expected code does not work for me. What am I doing wrong? results is always invalid. Thank you
let keypathExp1 = NSExpression(forKeyPath: "computer")
let expression = NSExpression(forFunction: "sum:", arguments: [keypathExp1])
let sumDesc = NSExpressionDescription()
sumDesc.expression = expression
sumDesc.name = "sum"
sumDesc.expressionResultType = .integer64AttributeType
let request = NSFetchRequest(entityName: "department")
request.returnsObjectsAsFaults = false
request.propertiesToFetch = [sumDesc]
request.resultType = .dictionaryResultType
let fetch: NSFetchRequest = department.fetchRequest()
do{
let results = try? fetch.execute()
print(results ?? "invalid?") // results is now an array
}
catch {
NSLog("Error fetching entity: %@", error.localizedDescription)
}
Edit: put source in code block for clean formatting
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First things first...
When posting code to these forums, place three backticks ``` on the line before your code and three backticks ``` on the line after your code so that it will be formatted properly. You can also highlight an entire code block and click the </> button on the toolbar to wrap the block for you.
This makes it far easier to read and also makes it easier for other posters to copy/paste the code in order to test solutions and such.
Doing this will ensure that you end up with something like this:
let keypathExp1 = NSExpression(forKeyPath: "computer")
let expression = NSExpression(forFunction: "sum:", arguments: [keypathExp1])
let sumDesc = NSExpressionDescription()
sumDesc.expression = expression
sumDesc.name = "sum"
sumDesc.expressionResultType = .integer64AttributeType
let request = NSFetchRequest(entityName: "department")
request.returnsObjectsAsFaults = false
request.propertiesToFetch = [sumDesc]
request.resultType = .dictionaryResultType
let fetch: NSFetchRequest = department.fetchRequest()
do{
let results = try? fetch.execute()
print(results ?? "invalid?") // results is now an array
} catch {
NSLog("Error fetching entity: %@", error.localizedDescription)
}
instead of this:
let keypathExp1 = NSExpression(forKeyPath: "computer") let expression = NSExpression(forFunction: "sum:", arguments: [keypathExp1]) let sumDesc = NSExpressionDescription() sumDesc.expression = expression sumDesc.name = "sum" sumDesc.expressionResultType = .integer64AttributeType
let request = NSFetchRequest(entityName: "department") request.returnsObjectsAsFaults = false request.propertiesToFetch = [sumDesc] request.resultType = .dictionaryResultType
let fetch: NSFetchRequest = department.fetchRequest() do{ let results = try? fetch.execute() print(results ?? "invalid?") // results is now an array } catch { NSLog("Error fetching entity: %@", error.localizedDescription) }
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Sorry it's taken me so long to respond; real life got in the way for a while.
Anyway, check out this simple sample project I uploaded to github: roosterboy/CoreDataFunctions
Hopefully, this will give you a good idea how to do what you are looking to do.
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thanks so much for the reply @roosterboy. Taking a look at this solution now. Will reply back
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sorry that it has been this long, but I have finally been able to download and run this code. And it seems to suit my purpose, thanks for putting it together, especially the sweet preview readme file. I am going to dig in and add this to my project. Stay tuned!
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Hello,
In response to https://www.hackingwithswift.com/forums/swift/data-from-multiple-entities-into-array-for-math-ops/18754/18881 above, I have cloned and tested that project and it works great!
I have adapted it to my project, and it works in some capacity there too. My project (weight lifting data logger) has core data for a number of exercises and each exercise has one or more sets. Sets contain a weight lifted and the number of repetitions completed. I am able to fetch the maximum weight lifted across sets of all exercises (bench press, squat, etc), which is good, however I would like to fetch the max weight of all sets limited to a given exercise. How can I accomplish this? I expect that an NSPredicate may be part of the solution, but I am not able to find something working in a search. Alternatively, I believe it could be by exercising the relationship from set to exercise (which is an inverse relationship in my data). Any help is appreciated.
The function that I have and is working now to get max of all sets in the data:
func maxSetWeight() -> Float {
let request = NSFetchRequest<NSDictionary>(entityName: "Set")
request.resultType = .dictionaryResultType
let maxWeightExpression = NSExpressionDescription()
maxWeightExpression.expressionResultType = .floatAttributeType
// max, min, sum, average
maxWeightExpression.expression = NSExpression(forFunction: "max:", arguments: [NSExpression(forKeyPath: "weight")])
maxWeightExpression.name = "maxSetWeight"
request.propertiesToFetch = [maxWeightExpression]
let result = try! container.viewContext.fetch(request) as! [[String: AnyObject]]
let maxSetWeight = result[0]["maxSetWeight"] as? Float ?? 0.0
return maxSetWeight
}
My data model:
Exercise {String name}
Set {UUID id, Float weight, Int16 reps} has relationship {exercises} Destination {Exercise} Inverse {sets}
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bump, still looking for suggestions on this! thanks
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You can achieve this by fetching the entities and extracting the 'price' field into an array. Here's a quick example in Python:
# Assuming 'homes' is your collection of entities
prices = [home['price'] for home in homes]
# Now, find the max price
max_price = max(prices)
# 'max_price' holds the maximum price value
Feel free to adapt it to your specific implementation.
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bump, still looking for suggestions on this! thanks
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