使用其他解析查询的结果过滤解析查询不起作用-Swift

Question

I have set up my Parse backend in my Swift app so that I have a class with Paintings and another one with Users.

I also have a class with pointers to both paintings and users, so that each user can rate paintings:

In my main table view I want to load all the paintings that the current logged in user has rated. To do this I am using this code:

var paintingArray: [AnyObject] = []

// Define the query that will provide the data for the table view
override func queryForTable() -> PFQuery {

    //Find User Painting Relations to display
    var relationQuery = PFQuery(className:"UserPaintingRelation")
    relationQuery.whereKey("userID", equalTo:PFUser.currentUser()!)

    relationQuery.findObjectsInBackgroundWithBlock {
        (objects: [AnyObject]?, error: NSError?) -> Void in

        if error == nil {
            // The find succeeded.
            // Do something with the found objects
            if let objects = objects as? [PFObject] {
                for object in objects {
                    println(object.objectId)

                    //Add the paintingID of the current object to array 
                    var paintingObjectId: AnyObject? = object["paintingID"]!.objectId
                    var paintingObjectIdString:String = paintingObjectId as! String
                    self.paintingArray.append(paintingObjectIdString)                       
                }

            }
        } else {
            // Log details of the failure
            println("Error: \(error!) \(error!.userInfo!)")
        }

    }

    //Query that loads relevant Painting objects
    var query = PFQuery(className: "Painting")
    //Make sure only the objects that are referenced in the paintingArray are loaded
    query.whereKey("objectId", containedIn: self.paintingArray)

    return query
}

This code does not throw any errors. However, in the simulator my table view appears to be empty. If I use a correct paintingID to filter my query:

query.whereKey("objectId", equalTo:"yd62zCrXR7")

instead of:

query.whereKey("objectId", containedIn: self.paintingArray)

one object shows up in the table view.

This leads me to believe that the second query is executed before the array has been filled with the correct strings, which results in the table view not loading any objects. Is this assumption correct? And if so, is there anyway I can make sure that the paintingArray finishes loading all the strings from the relationQuery before my second query executes?

Many thanks, all help is greatly appreciated! Still quite new at Swift so can't really wrap my head around what is wrong.

Answer 1

Edited your code as I commented. In your case the parse call for userPaintingRelation is a background thread will be executed in background whereas the Paintings query executed before the background query is executed.

var paintingArray: [AnyObject] = []

// Define the query that will provide the data for the table view
override func queryForTable() -> Void {

//Find User Painting Relations to display
var relationQuery = PFQuery(className:"UserPaintingRelation")
relationQuery.whereKey("userID", equalTo:PFUser.currentUser()!)

relationQuery.findObjectsInBackgroundWithBlock {
    (objects: [AnyObject]?, error: NSError?) -> Void in

    if error == nil {
        // The find succeeded.
        // Do something with the found objects
        if let objects = objects as? [PFObject] {
            for object in objects {
                println(object.objectId)

                //Add the paintingID of the current object to array 
                var paintingObjectId: AnyObject? = object["paintingID"]!.objectId
                var paintingObjectIdString:String = paintingObjectId as! String
                self.paintingArray.append(paintingObjectIdString)                       
            }
          //Query that loads relevant Painting objects
          var query = PFQuery(className: "Painting")
          //Make sure only the objects that are referenced in the paintingArray are loaded
          query.whereKey("objectId", containedIn: self.paintingArray)
          var: tableArray = query.findObjects() as [PFObject] //array for datasource of table
          yourTableView.reloadData()
        }
    } else {
        // Log details of the failure
        println("Error: \(error!) \(error!.userInfo!)")
    }

}
}

Answer 2

I solved this issue by not using relationQuery.finObjectsInBackgroundWithBlock {} but instead using relationQuery.findObjects{} as that operation will not be executed in the background, which makes sure that my array paintingArray will be filled with strings before the second query is executed.

Here is the code I ended up with. Not perfect by any means, but it works for now.

let emptyArray: [AnyObject] = []
var paintingArray: [AnyObject] = []     
override func queryForTable() -> PFQuery {

    //Find User Painting Relations to display
    var relationQuery = PFQuery(className:"UserPaintingRelation")
    relationQuery.whereKey("userID", equalTo:PFUser.currentUser()!)

    var paintings = relationQuery.findObjects() as! [PFObject]
    for painting in paintings {
        var paintingObjectId: AnyObject? = painting["paintingID"]!.objectId
        var paintingObjectIdString:String = paintingObjectId as! String
        self.paintingArray.append(paintingObjectIdString)
    }

    var query = PFQuery(className: "Painting")
    query.whereKey("objectId", containedIn: self.paintingArray)

    //Empty array so that tableview reloads completely when table is reloaded
    self.storeArray = self.emptyArray

    return query
}