计算领域对象列表中的项目数不起作用

Question

I'm trying to count the number of exercises in a Realm List (contained within a "WorkoutSessionObject") to populate the right number of rows for a tableview but for some reason I can't work out it isn't letting me access the property?

It's definitely retrieving the WorkoutSessionObject because I've tried printing it.

Here's the code :

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

//filter for a specific workout
    let predicate = NSPredicate(format: "workoutID = %@", workoutID)
    let workoutExercises = realm.objects(WorkoutSessionObject.self).filter(predicate)

//access the 'exercises' list and count it - this isn't working?
    let numberOfExercises = workoutExercises.exercises.count
    return numberOfExercises
}

I've accessed the properties in a similar way for populating the cells but I'm obviously using index.row there.

The error I'm getting is

Value of type 'Results' has no member 'exercises'

on the line that is marked as not working in the code

Research there is an answer here Retrieve the List property count of realm for tableview Swift but that doesn't seem it would return the count in scope (it allows a print in the example but this isn't working in my code)

ie I've also tried this, which doesn't work because the count isn't accessible outside the scope :

   func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        let predicate = NSPredicate(format: "workoutID = %@", workoutID)

//the below works to count but then not accessible outside scope to define number of rows :-(

        let workoutExercises = realm.objects(WorkoutSessionObject.self).filter(predicate)
        for exercises in workoutExercises {
            let exerciseCount = exercises.exercises.count
            return exerciseCount
        }
//return exercise count for table rows - this doesn't work because not in scope
        return exerciseCount
    }

Any ideas?

Answer 1

The issue is that Realm's filter keeps the original type (just like Swift's built-in filter ), so the type of workoutExercises will actually be Results<WorkoutSessionObject> and not a single WorkoutSessionObject .

If you know that the workoutID property of the WorkoutSessionObject is always unique, you can simply call first on the Results instance.

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    let predicate = NSPredicate(format: "workoutID = %@", workoutID)
    let workoutExercises = realm.objects(WorkoutSessionObject.self).filter(predicate).first
    return workoutExercises?.exercises.count ?? 0
}

If you know that there will always be a matching WorkoutSessionObject , you can force unwrap workoutExercises .

If workoutID is actually a primaryKey, its even better to use let workoutExercises = realm.object(ofType: WorkoutSessionObject.self, forPrimaryKey: workoutID) instead of the filtered query.