Run CKQueryOperation with results from previous CKQueryOperation - swiftui

Question

I have an app that is a shopping list. I can store prices per product and vendor in my app, the model is
Product
Vendor
Price
One product can have multiple prices from different vendors.
I store the price information with references to the product and vendor (CKRecord.Reference).
Now I am using the below to fetch all the prices related to a product:
public func fetchDataByProduct(product: Product, completionHandler: #escaping (Bool) -> Void){
self.pricesBuffer = []
let cloudContainer = CKContainer.init(identifier: "iCloud.XYZ")
let publicDatabase = cloudContainer.publicCloudDatabase
let reference = CKRecord.Reference(recordID: product.recordID, action: .deleteSelf)
let predicate = NSPredicate(format: "priceToProduct == %#", reference)
let query = CKQuery(recordType: "Price", predicate: predicate)
let operation = CKQueryOperation(query: query)
operation.recordFetchedBlock = { record in
let price = Price()
price.recordID = record.recordID
price.grossPrice = record.object(forKey: "grossPrice") as? Double
let dummy = record.object(forKey: "priceToVendor") as! CKRecord.Reference
price.vendorRecordID = dummy.recordID
self.pricesBuffer.append(price)
}
operation.queryCompletionBlock = { [unowned self] (cursor, error) in
self.pricesBuffer.forEach({price in
price.retrieveVendor()
})
DispatchQueue.main.async {
if error == nil {
self.prices = self.pricesBuffer
completionHandler(true)
} else {
}
}
}
publicDatabase.add(operation)
}
My problem is now that I cannot retrieve the vendor name which is part of the Vendor object (Vendor.name).
I have tried to loop over the pricesBuffer and run this one per price but the problem seems to be that CloudKit first completes the initial request to fetchDataByProduct() and then afterwards fetches the vendor data but then its too late because that updated data does not get pushed to my View (SwiftUI).
publicDatabase.fetch(withRecordID: self.vendorRecordID, completionHandler:  {[unowned self] record, error in
if let record = record {
print(record)
self.vendor.recordID = record.recordID
self.vendor.name = record["name"] as! String
print(self.vendor.name)
}
})
Any ideas how to solve this? I believe I have to add a second CKQueryOperation to the mix and use the .addDependency() but I cannot wrap my head around how that should look like in the end.

Answer 1

Let's say you use the operation to fetch prices like above.
let predicate = NSPredicate(format: "priceToProduct == %#", reference)
let query = CKQuery(recordType: "Price", predicate: predicate)
let pricesOperation = CKQueryOperation(query: query)
pricesOperation.database = publicDatabase // not required if you don't use OperationQueue
Then you can construct operation to fetch vendors, I will create simple operation for demo purposes.
let vendorQuery = CKQuery(recordType: "Vendor", predicate: predicate)
let vendorsOperation = CKQueryOperation(query: vendorQuery)
vendorsOperation.database = publicDatabase // not required if you don't use OperationQueue
Then you can set dependency, first fetch prices than vendors.
vendorsOperation.addDependency(pricesOperation)
And lastly submit those operations to OperationQueue
let operationQueue = OperationQueue()
operationQueue.addOperations([pricesOperation, vendorsOperation], waitUntilFinished: false)
Edit: If you don't want to use OperationQueue, simply submit those operations to database, but first set dependency before submitting the operations to be executed.
vendorsOperation.addDependency(pricesOperation)
publicDatabase.add(pricesOperation)
publicDatabase.add(vendorsOperation)