I am curious is it somehow possible to increment a field value in a CKRecord variable without fetching? So on client I am not curious about the recent value, I just want to increase whatever be the value is. The reason, operation should be as quick and easy as possible, instead of two message 'stream', I want initiate only one.
Unfortunately you can not. You have to read, change and then write the record. Make sure that you use the CKModifyRecordsOperation and leave the savePolicy to CKRecordSaveIfServerRecordUnchanged If you get an error then you could try read and write the record again.
Related
Swift / iOS
Can anyone tell me if it is possible to specify the PFObject objectId value when creating new objects?
I've obviously attempted but the save fails. (which might just be the answer)
The reason I am asking is I wondered if anyone had found a "trick" that would allow me to specify.
I am using PFObject.saveInBackground { method to persist the new object.
No you can not. Parse sets the objectId on the server during the save operation.
The reason your operation is failing is because Parse is looking for an object on the server with the id that you are specifying and is then trying to update that object but it cannot find the object.
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'm building a messaging application. I update the badge count in the database via a sqlite trigger whenever any operation like insert/delete/read message happens.
Currently, though the value update in the DB happens asynchronously, I have no way to get notified about when the value changes in my application and hence am polling periodically.
Is there some way to setup an observer on a database value/publish some notification when a given value changes?
I know that I can do this easily by first updating the badge count in an in-memory property and then persisting the changes to the DB; but I am not very inclined to do this, since there are too many entry points for this value to change, and I don't want to add a SET property everywhere.
One possible option would be to define a trigger that is only called when this specific value in the database is updated. The trigger should then make a call to a user defined function you create in your app. You use the sqlite3_create_function function to add your own function to SQLite. Your trigger would like something like:
CREATE TRIGGER some_trigger_name
AFTER UPDATE OF some_column ON some_table
FOR EACH ROW BEGIN
SELECT my_custom_fuction();
END;
If needed, you can pass 1 or more arguments to your function.
Though that this might not be an option for you, Core Data does this well.
An object needs to be submitted to the server, and I want to indicate to the user that the object needs to be submitted by displaying the lastModified date/time, and lastSubmitted date/time.
(Yes, the record must be manually submitted.)
I'm currently listening for NSManagedObjectContextObjectsDidChangeNotification, checking if the object's entity is RetailLocation, and if so, setting its lastModified date/time (of course, only if lastModified is not the only property being modified). Since this seems to highly confuse the undo manager, I use performSelector:SOMESEL withObject:retailLocation afterDelay:0.0 to set the lastModified property.
Sadly, this is almost even worse: this results in two actions being added to the undo stack!
Can someone recommend a nice way to implement a lastModified attribute in a Core Data-managed record? Alternatively, what am I missing?
If you don't want the modification date to be undoable, you can call disableUndoRegistration on your NSUndoManager before making changes, and enableUndoRegistration when you're done.
If you need one, you can get a pointer to the NSUndoManager by calling undoManager on your NSManagedObjectContext, but if you're working in iOS you should have one already.
Also, note Apple recommends using the NSManagedObjectContextWillSaveNotification notification for this, since changes might not necessarily be saved.
What is wrong in this code?
I was expected "titi" in person.name but I still have "toto"!
More explicitly, how to modify a record in a function?
init1()->
S=#person{name="toto"}, %record creation and field setting
fct(S),
io:format("~s~n",[S#person.name]).
fct(R)->
R#person{name="titi"}. %record updating
You need to get a result of fct():
init1()->
S=#person{name="toto"}, %record creation and field setting
S2 = fct(S), % Get updated record
io:format("~s~n",[S2#person.name]).
fct(R)->
R#person{name="titi"}. %record updating
Bertaud, I think you are getting ahead of yourself a bit. You really need to understand the basics of immutability before you write any more code. (i.e. "variables" do not vary : you can only assign a value to them once.) I suggest you read the free online guide "Learn You Some Erlang For Great Good", at http://learnyousomeerlang.com/. The section that covers the basics of variables is http://learnyousomeerlang.com/starting-out-for-real#invariable-variables.
It is impossible to stress too much that all data in Erlang is immutable. So to do something like in your original question you need to modify it like #hdima did. The record is not updated but rewritten. In the same way there is no global data in Erlang, all data belongs to a process. This is even true of ETS tables as they basically behave like a process, albeit a built-in one without explicit communication.
So if you use the process dictionary or an ETS table the data itself can never be updated, only the dictionary/table. This means that to modify some data in the dictionary/table you basically have to:
"Read" the data
Update the data making new data
"Write" the new back into the dictionary/table
Without writing the new data back into the dictionary/table it will be lost, as your new data was.
Within fct(), you're not mutating the record, but you're returning a new value for the record, which needs to be used further. If you're calling fct(S), without handling the return value, then you'll lose that new value ("titi").