Using Core Data to Increment a count on an entity (Twitter CS193p)

I'm completing the CS193 Stanford course, and am using Core Data to store tweets as part of a Twitter client.

However, when I find a hashmention that is existing, I want to increment the hash.count representing how many matches I have, but no matter how many matching hashmentions there are hash.count only ever stores 0 or 2 (i.e. the attribute is not functioning as persistent storage on the entity).

class HashMention: NSManagedObject {
static func findOrCreateHashMention(matching twitterInfo: Twitter.Mention, in context: NSManagedObjectContext) throws -> HashMention
{
    let hash = HashMention (context: context)
    let request : NSFetchRequest<HashMention> = HashMention.fetchRequest()
    request.predicate = NSPredicate(format: "text =[cd] %@", twitterInfo.keyword)
    do {
        let matches = try context.fetch(request)
        if matches.count > 0 {
            //inc count
            hash.count =  Int32(Int(matches.count) + 1)

            return hash
        }
        else{
            hash.count = 0
            print("zero hash:", twitterInfo.keyword)
            hash.text = twitterInfo.keyword.lowercased()
            return hash
        }
    }
    catch{
        //makes this function throw
        throw error
    }
}
}

So matches itself needed to be changed - but is in an array in the example above. Therefore the answer was the following:

do {
        let matches = try context.fetch(request)
let mention = matches.first
        if matches.count > 0 {
            mention?.count = (mention?.count)! + 1
//.. more code