Pinning relation pointer data

Client SDKs iOS SDK 📱⌚️💻
#1

A query returns containing 1 field that is a relation to another class, which I would like to pin into the Local Datastore.

If I use a SQLite browser, I can see this pinned class / query result. But I cannot see the “related” class.

My understanding from the documentation is that:

Pinning a PFObject is recursive, just like saving, so any objects that are pointed to by the one you are pinning will also be pinned.

https://docs.parseplatform.org/ios/guide/#pinning

But that doesn’t seem to be happening here. Are Relations handled differently?

#2

Could you share the code you are using? You probably need to also query and pin the relation data.

#3 
func getCurrentComp(withId compId: String, isLocal: Bool) {
        let query = PFQuery(className: "Competition")
        query.includeKey("Rounds") // THIS IS THE RELATION FIELD - TESTING IF THIS WOULD HELP - IT DOESN'T
        
        if isLocal {
            query.fromLocalDatastore()
        }
        
        
        query.getObjectInBackground(withId: compId, block: { (object, error) in
            if let error = error {
                print("Get Current Comp Error: \(error)")
            }
            
            if let compObject = object {
                print("Get Current Comp compObject: \(compObject)")
                if !isLocal {
                    
                    compObject.pinInBackground(withName: "CurrentComp") { (success, error) in
                        if let error = error {
                            print("Get Current Comp Pin Error: \(error)")
                        }
                        
                        if success {
                            print("Get Current Comp Pinned")
                        }
                    }
                }
                self.dataManager.selectedComp = compObject
            }
        })
    }

Which returns (from print statements):

Get Current Comp compObject: <Competition: 0x600003bc6820, objectId: CXy40U65Z9, localId: (null)> {
Name = “Competition 1”;
Played = “2020-08-27 09:19:16 +0000”;
Rounds = “<PFRelation: 0x600001f92c80, 0x0.(null) -> Course>”;
}
Get Current Comp Pinned

#4

I have been testing using Arrays of objects (classes?), rather than Parse Relations to create this relationship, taken again from the iOS documentation.

The pinning recursion seems to function as I had originally expected from the documentation in this way. It was a simple test with 2 classes:

TestClass1 - created 2 objects
TestClass2 - created 1 object, with a “Linked” field of type Array

Query for the first (single) TestClass2 object, to assign it as a PFObject.

Then testClass2.add(linkedClass, forKey: "Linked")

Now if I query for this object again AND pin it, when I view this in the SQLite browser I can see both classes having been pinned (TestClass2 has 1 row / object, TestClass1 has 2 rows / objects). Nothing else was required.

Should this pinning of related classes / objects work with Relations or Pointers as well? Or will I need to perform additional sub-queries of the linked items? Is this the reason for the following statement in the documentation?

In general, using arrays will lead to higher performance and require fewer queries

#5

You will have to do an additional query to retrieve the relations and then pin them. You can easily create a new query for your relation with something like this:

// suppose we have a book object
let book = ...

// create a relation based on the authors key
let relation = book.relationForKey("authors")

// generate a query based on that relation
let query = relation.query()

// now execute the query

Then you can use PFObject.pinAllInBackground(listOfObjects) to pin the results.