如何使用CloudKit通过CKQueryOperation进行迭代查询，直到游标为nil？

Question

How would I declare a closure that retrieves records from CloudKit that iteratively calls itself until all the records are fetched? The following code does that, except I get an error saying

Variable used within its own initial value

at the line where I assign the closure queryCompletionBlock to the property by that same name of the query operation within the declaration of the closure itself. Basically, I get an error because I call the closure within itself in the declaration of the closure before the closure is declared.

    let predicate = NSPredicate(value: true)
    let query = CKQuery(recordType: DatabaseNameStrings.recordTypeEntry, predicate: predicate)
    let queryOperation = CKQueryOperation(query: query)
    queryOperation.desiredKeys = [DatabaseNameStrings.fieldNameCreatedAt, DatabaseNameStrings.fieldNameText]
    let queryCompletionBlock = {
        (cursor: CKQueryOperation.Cursor?, error: Error?) in
        if let error = error {
            print(error.localizedDescription)
        } else if let cursor = cursor {
            let queryOperation = CKQueryOperation(cursor: cursor)
            queryOperation.desiredKeys = [DatabaseNameStrings.fieldNameCreatedAt, DatabaseNameStrings.fieldNameText]
            queryOperation.queryCompletionBlock = queryCompletionBlock // Error message "Variable used within its own initial value"
            queryOperationQueue.addOperation(queryOperation)
        }
    }
    queryOperation.queryCompletionBlock = queryCompletionBlock
    queryOperationQueue.addOperation(queryOperation)

Answer 1

One option that should work is to reference the queryCompletionBlock of the original query operation.

let predicate = NSPredicate(value: true)
let query = CKQuery(recordType: DatabaseNameStrings.recordTypeEntry, predicate: predicate)
let queryOperation = CKQueryOperation(query: query)
queryOperation.desiredKeys = [DatabaseNameStrings.fieldNameCreatedAt, DatabaseNameStrings.fieldNameText]
let queryCompletionBlock = {
    (cursor: CKQueryOperation.Cursor?, error: Error?) in
    if let error = error {
        print(error.localizedDescription)
    } else if let cursor = cursor {
        let newOperation = CKQueryOperation(cursor: cursor)
        newOperation.desiredKeys = queryOperation.desiredKeys
        newOperation.queryCompletionBlock = queryOperation.queryCompletionBlock
        newOperationQueue.addOperation(newOperation)
    }
}
queryOperation.queryCompletionBlock = queryCompletionBlock
queryOperationQueue.addOperation(queryOperation)