Question

我已经在我的Swift应用程序中设置了Parse后端，以便我有一个有绘画的课程和另一个有用户的课程。

我还有一个指向绘画和用户指针的课程，因此每个用户都可以对绘画进行评分： enter image description here

在我的主表视图中，我想加载当前登录用户已评级的所有绘画。为此，我使用此代码：

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
}

此代码不会引发任何错误。但是，在模拟器中，我的表视图显示为空。如果我使用正确的paintingID来过滤我的查询：

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

而不是：

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

一个对象显示在表视图中。

这让我相信第二个查询是在数组填充正确的字符串之前执行的，这会导致表视图不加载任何对象。这个假设是否正确？如果是这样，无论如何我可以确保在第二次查询执行之前，paintingArray完成从relationQuery加载所有字符串吗？

非常感谢，非常感谢所有帮助！在Swift上还是很新的，所以无法真正理解错误。

Answer 1

按照我的评论编辑了您的代码。在您的情况下，对userPaintingRelation的解析调用是后台线程将在后台执行，而绘图查询在执行后台查询之前执行。

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

我通过不使用relationQuery.finObjectsInBackgroundWithBlock {}解决了这个问题，而是使用relationQuery.findObjects{}，因为该操作不会在后台执行，这确保我的数组paintingArray将在第二个查询之前填充字符串被执行。

这是我最终得到的代码。无论如何都不完美，但它现在有效。

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
}

使用其他Parse查询的结果过滤Parse查询 - Swift

2 个答案: