Merging Two Parse Tables in a Query

Question

I have two parse classes, one is "users" and one is where users enter some comments like "tweets". In "users" class every object has two columns a username and a photo. In tweets table every object has the info of username and comment. I need to make a query that merges these two tables according to username matches, and finally should have 3 columns, username - photo - comment. How can I do this via swift in xcode? Than I will use the result append it as arrays and show them in table view cells.

sergio · Accepted Answer · 2015-06-05T10:19:14.773

2

You should take a look at Parse 1-many relationships. Here you can find Swift-based code snippets.

Basically, you do not link a user's tweets to that user by associating the user name (this is what would happen in a SQL database). What you do is assigning a user object to the tweets, then when you have a tweet, you can access its user attribute and all of its properties.

let user = PFObject(className:"TweetAuthor")
...
let tweet = PFObject(className:"Tweet")
tweet["..."] = ...
tweet["createdBy"] = user
...
let userTweets = PFQuery(className:"Tweet")
tweetQuery.whereKey("createdBy", equalTo: user)
tweetQuery.findObjectsInBackgroundWithBlock {
      (objects: [AnyObject]?, error: NSError?) -> Void in

    let aTweet = object![...]
    let picture = aTweet["createdBy"]["picture"]
    ...
}

Hope this helps.

EDIT:

How should you use the code above?

I assume that at some place in your app, you create a Tweet and you currently assign it a 'username' (and 'profilePicture', etc.):

tweet["userName"] = user["username"]

Instead of assigning a userName (string), assign it the full user object:

tweet["createdBy"] = user

(remove all code to assign profilePicture, etc.)

Once you have this, you can get the picture associated to a tweet by doing:

let picture = aTweet["createdBy"]["picture"]

edited Jun 05 '15 at 10:19

answered Jun 05 '15 at 09:14

sergio

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Hello Sergio, http://i.imgur.com/5CN5K5m.png and http://i.imgur.com/fkstCWw.png are the views of my table. I could not understand well what I should fill the dots with in your code. I am a bit new in swift coding. The classes are "Usertable" and "tweets". I would be really happy if your could make your code a bit clearer :) thank you very much – saner Jun 05 '15 at 09:53
I see. That kind of design is suboptimal for Parse (or other NoSQL databases). Why can't you store your full user object in a tweet? you would also avoid having to store separately the email address and the user name... Have a look at this for the "suboptimal" bit: https://parse.com/questions/how-to-join-several-tables-with-one-to-many-relationship – sergio Jun 05 '15 at 10:02
@saner: please show me your code where you create tweets, and assign them a username... the dots are basically whatever code you have -- I am just showing the relevant bits... – sergio Jun 05 '15 at 10:03
Actually I used to store all the data including picture in tweets table, but I have also a users table in which users have their profile picture. I have a setting in which users update their profile pictures. When a user updates the profile picture it takes too much time for the tweets table to be updated as hundreds of objects' profile picture needs to be updated. – saner Jun 05 '15 at 10:08
yeah, you are doing a lot of work that is unnecessary and will necessarily slow down your app. the way to go is what I outlined above. See my edit, I hope it clarifies things a bit. – sergio Jun 05 '15 at 10:19

score 0 · Answer 2 · answered Jun 05 '15 at 10:12

The code below that I use thats the info of the people who is followed by the current user, and shows their tweet info. However when a user updates his profile picture which is in the users table, the past data of the tweets table (which includes also the profile picture) is not updated.

func refreshResults() {

    followArray.removeAll(keepCapacity: false)
    resultsNameArray.removeAll(keepCapacity: false)
    resultsUserNameArray.removeAll(keepCapacity: false)
    resulltsImageFiles.removeAll(keepCapacity: false)
    resultsTweetArray.removeAll(keepCapacity: false)
    resultsHasImageArray.removeAll(keepCapacity: false)
    resultsTweetImageFiles.removeAll(keepCapacity: false)
    resultsTweetType.removeAll(keepCapacity: false)

    var followQuery = PFQuery(className: "follow")
    followQuery.whereKey("user", equalTo: PFUser.currentUser()!.username!)
    followQuery.addDescendingOrder("createdAt")

    var objects = followQuery.findObjects()

    for object in objects! {

        self.followArray.append(object.objectForKey("userToFollow") as! String)

    }

    var query = PFQuery(className: "tweets")
    query.whereKey("userName", containedIn: followArray)
    query.addDescendingOrder("createdAt")

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

        if error == nil {

            for object in objects! {

                self.resultsNameArray.append(object.objectForKey("profileName") as! String)
                self.resultsUserNameArray.append(object.objectForKey("userName") as! String)
                self.resulltsImageFiles.append(object.objectForKey("photo") as! PFFile)
                self.resultsTweetArray.append(object.objectForKey("tweet") as! String)
                self.resultsHasImageArray.append(object.objectForKey("hasImage") as! String)
                self.resultsTweetImageFiles.append(object.objectForKey("tweetImage") as? PFFile)
                self.resultsTweetType.append(object.objectForKey("tweetType") as! Int)
                self.resultsTable.reloadData()

            }

            self.refresher.endRefreshing()

        }
    }

}

score 0 · Answer 3 · answered Jun 05 '15 at 12:53

I could not figured it out how to record a column in parse of an object from another table. As you stated, I am currently recording the username and photo seperately as columns for each tweet. The tweeting code is as below. In parse should I create a new column for this in the tweets table? What should be the type of the column?

var tweetObj = PFObject(className: "tweets")

    tweetObj["userName"] = PFUser.currentUser()!.username
    tweetObj["profileName"] = PFUser.currentUser()!.valueForKey("profileName") as! String
    tweetObj["photo"] = PFUser.currentUser()!.valueForKey("photo") as! PFFile
    tweetObj["tweet"] = theTweet

When I try to update the code above as the code below I get an error (I created the column in parse as type of object with name createdBy).

let user = PFObject(className:"TweetAuthor")

var tweetObj = PFObject(className: "tweets")

    tweetObj["userName"] = PFUser.currentUser()!.username
    tweetObj["profileName"] = PFUser.currentUser()!.valueForKey("profileName") as! String
    tweetObj["photo"] = PFUser.currentUser()!.valueForKey("photo") as! PFFile
    tweetObj["tweet"] = theTweet
    tweetObj["createdBy"] = user

Merging Two Parse Tables in a Query

3 Answers3