I am quite new with Parse, I am confused on how parse works.
Here I have a PFUser, PFGroupObject, PFUserGroupObject. Where PFUserGroupObject is a "Table" that relate user an group.
PFUserGroupObject and PFGroupObject is my custom PFObject
What confuses me is that, once I save the PFUserGroupObject, the PFGroupObject is also saved to Parse.
I have 2 questions:
Is this behaviour normal? I know that PFUserGroupObject has a variable that stores PFGroupObject. But, I am wondering if this is the expected behaviour of Parse.
//MARK - Create a New Group
var group: PFGroupObject = PFGroupObject();
group.name = "Friends Group";
//MARK - Create a Many to Many Join Table to Relate User and Group
var userGroup: PFUserGroupObject = PFUserGroupObject();
userGroup.user = PFUser.currentUser();
userGroup.group = group;
//THIS LINE CAUSES MY GROUP OBJECT TO BE SAVED TO PARSE AS WELL
PFObject.save(userGroup);
Let's say I called
PFObject.saveAll([group, userGroup]);
Would the group object saved twice into Parse?
I am trying to understand how Parse works.
Thank you!!!!!
When you save a "Parent" object that has one or more "child" objects, it will save the children as well. I have never worked with PFGroupObjects, but I have a pointer to a custom object attached to each of my users. Rather than having to save my custom object, then save my user (or vice versa), saving just my user will also save my custom object.
There are some nuances with this, such as trying to add a pointer to an unsaved object which you have just created to another object, then saving the parent. While you generated an object id when you created the child object, you haven't actually saved it, so it's a dangling pointer.
Hope this helps!
edit - If you want to see exactly what is getting saved when, add a before save trigger to your cloud code for the object you want to see whether or not is being saved multiple times, with a console print line inside. Do some testing, and check your logs to see how many times the beforeSave trigger is getting called, and that's how many times you are attempting to save an object of that type.
Related
I am using Entity's Object ID in order to uniquely identify local notifications and modify them. I observed that first time when I save my entity, it has following object ID:
<x-coredata:///Task/tE1C5A230-A419-42D5-AF78-3327A09D13BD2>
If I don't exit my application, and try to modify notification, object ID doesn't change and I can modify my notification.
Now, if I restart my app and try to access that entity again, it has different object ID:
<x-coredata://D6703834-ECB4-487B-84F8-330A215E16B7/Task/p13>
So I can't modify notification, as object ID for entity is different. Interesting thing is whenever I access that entity, Object ID remains same as the last one.
So my Question here is why Core data shows different object ID for the first time entity is created? When I try to access entity after opening app again for many times, the object ID (different than the first one) remains constant. I am curious to know why is it happening so?
Please note:
I know there are many posts on SO pointing out that using Object ID is not a reliable approach. Still I want to know reason that why two IDs are being shown.
the first OID is a temporary OID - a temporary id denotes objects that have not been saved yet. the 2nd id is a permanent one and is assigned to a MO AFTER it has been saved:
so...
var objectID = object.objectID
if objectID.temporaryID {
object.managedObjectContext.save() //try do catch left out
}
objectID = object.objectID
assert(objectID.temporaryID == false)
I'm creating two PFObjects at the same time that should reference each other's object IDs when they're saved. In the example below, the second object is supposed to save the first object's object ID in an array.
let objectForFirstClass = PFObject(className:"ClassOne")
let objectForSecondClass = PFObject(className: "ClassTwo")
objectForSecondClass.setObject([objectForFirstClass.objectId!], forKey: "classOneObjectArray")
The last line is causing the error because objectForFirstClass.objectId is nil. I'd assume this is because the object hasn't been saved yet. How can I fix this?
You want to save after creating the first object, and in the completion handler, create the second one with a reference to the first one.
You can use saveAllInBackground:block: for this.
Correct, the object id is assigned by the server when saved. I'd be tempted to write some cloud code to do what you want so you can send some details and the cloud code will create and connect the objects, then return both of them to you. You can of course do the same thing locally in your app, there's just more network comms.
You should also consider using pointers or relationships. These are better for querying, though the same save requirements apply before you can set the connections.
I am in a situation where I allow the user to download a PFObject and modify it locally, and they can then either cancel the changes or hit Done, which will dismiss the editing interface but NOT upload the changes to Parse yet. They need to hit Save on the previous screen to write all changes to the database at once.
The problem is once the PFObject is modified, you cannot revert it to its prior state without refetching from the database. But I cannot always refetch the data from the database every time they hit Cancel because the prior state may not be uploaded to Parse yet (and that's a bad UX making them wait to discard changes that are only stored locally).
For example, imagine the user taps to edit the PFObject, they make changes then hit Done, then tap on it again and further edit the object, then hit Cancel. In this case, the object needs to be reverted to its prior state, but that state has not been uploaded to Parse yet. So I cannot refetch the data from the database to revert changes otherwise it would overwrite the changes they made the first time.
To solve this problem, I would simply fetch the PFObject and store a copy of it. I'd call that the transient object. I would have another property that stores the real object. The user would modify the transient object, and when they hit Cancel I would simply set that to nil, if they instead hit Done I would set the real object equal to the transient object, and once they finally hit Save I would save the real object to the database. That way I can be sure changes aren't being made to the real object until the user commits the changes. The problem is, PFObject does not adopt the NSCopying protocol (not sure why), therefore I cannot create a copy of the PFObject. Any change I make to it affects the real object.
How can this be resolved, without modifying the app's design that allows control over when the data is committed and later saved? Is there a way to extend PFObject and adopt NSCopying, has it been done before?
I did consider storing the attributes of the object in a dictionary and allow the user to edit that instead, then upon commit set each of those attributes on the PFObject. The problem with this solution arises with complex structures. In this app, I allow the user to modify multiple arrays that contain multiple PFObjects. It's just infeasible to try to recreate and later merge changes with complex structures like this beyond a single simple PFObject.
I ran into this same problem. I did not make any changes directly to the PFObject, but rather, saved the updates in an NSDictionary. When the user clicks the done button, I then update the PFObject and saveInBackground. I don't think there is a "discard local changes" option for PFObject. If you don't do this, the only option is to throw out the existing PFObject and fetch again.
Regarding the NSDictionary comment, perhaps NSArray would be better. The implementation really depends on your specific program, but I'll give a quick example. The NSArray we'll call instructionArray. Imagine there are 3 sections in a tableView. Also assume that the data source for each section is an NSArray of PFObjects. Now say you want to set the age property of each PFObject in Section 2 to 35.
Add an NSArray object (corresponding to an instruction to carry out) to the instructionArray. This instruction to carry out could have the form
Section to update
Property to update
Value to update to
So the object you'll add is #[#(2),#"age",#(35)];
Given that the user is probably carrying out a finite amount of instructions, it might not be that performance heavy to loop through the instructionArray in cellForRowAtIndexPath so when a cell uses its corresponding PFObject to figure out what to display, it can loop through the instructions after and change what is displayed as if the PFObject was updated.
When the save button is touched, loop through the instructions and actually edit the PFObjects themselves.
If you need the instructions to handle specific objects rather than sections, then you just have to update the structure of the instructionArray. Maybe you could include an identifier to indicate what type of instruction it is.
In Parse.com, the help document for updating an object seems to require a query first to retrieve the object before one can update the meta data.
Given that I know the objectId of the object I am updating, do I still have to make this additional call to retrieve everything else about the object before I can send an update call (via saveInBackground)?
Yes, you do. In order to update an object from parse, you must have a local copy.
In order to make a call to update an object - which can take several forms of save or saveInBackground or saveEventually, etc. - you must first make a query to have a copy of the object.
If you know the objectId, is sounds like you have already run a query on an associated object - why not get the full object then with an includeKey: call? https://www.parse.com/docs/ios_guide#queries-relational/iOS
I'm losing my mind around this question.
So I have a Core Data setup in my iOS app done this way:
http://www.cocoanetics.com/2012/07/multi-context-coredata/
I then insert an object by creating a temporary MOC (as explained in the blog post) and perform saves on all 3 contexts in performBlock: methods.
In a view controller I have an NSFetchedResultsController and it gets notified that I did indeed insert a new object. The problem is that the NSFetchedResultsChangeInsert is fired twice and each time the object that is passed trough has a different objectID (it also is a different object instance in memory). What happens is that I then have 2 rows inserted in my table view but un the SQL database there is only one new. It then of course crashes when I scroll to the bottom of the table view.
If I also perform some updates on the object I get NSFetchedResultsChangeUpdate called only once and with the objectID that was passed in the second NSFetchedResultsChangeInsert call.
The first ID looks like this:
<x-coredata:///ReceivedMessage/t605BB9A7-A04E-4B89-B568-65B12E8C259A2>
The second (and all consequent ones) like this:
<x-coredata://02A917C5-850F-4C67-B8E4-1C5790CF3919/ReceivedMessage/p28>
What could this be? Am I missing out something obvious?
PS: I also checked if the notification comes from the same context, thread, etc. It does.
The two IDs you are seeing may very well represent one object. The difference between them is just that the first one is a temporary object ID, assigned to the object on creation, and the second one is the permanent object ID, assigned to the object when it gets stored to the managed object store (see NSManagedObjectID's isTemporaryID).
To work around this issue you could call NSManagedObjectContext's obtainPermanentIDsForObjects:error: just before you save the temporary MOC. This way the inserted object will have just one ID during the save propagation and the NSFetchedResultsControllerDelegate methods should get called just once.