I'm having some problems storing a change to a complex object. I've done a lot of digging and can't figure this out for the life of me.
From debugging, I can clearly see that the object is correct before storing, but when I retrieve the stored data, it's empty(say the increase of a stat). Specifically here is the breakdown below
StatSheet has ArrayList of Players
Player has ArrayList of Stats
ArrayList of StatSheets -> ArrayList of Players -> ArrayList of Stats
The ArrayList of Stat objects doesn't store after a change is made, no matter what I do. The arraylist of players seems to update fine which confuses me. I have tried changing the update depth to 2, 3, 4, 5, and beyond. I have also tried specifically setting cascadeOnUpdate to true. Can someone please help, I've been at this for days.
It's been a while that I looked at db4o and you didn't give a lot of details about your environment or code but maybe you can look at these solutions:
Do you use web environment? So look at this first answer:
A few questions about working with db4o
Do you use 'commit' when you store your objects? Because after storing and updating process you should commit the changes.
The array list of objects is store but db4o don't know what to do with the inner objects. The ArrayList isn't 'Activatable', so you can't retrieve yours objects.
You must put activationPurpose on every getter/setter of your stored object to enable the activation of object.
As you can't do this on native java objects, DB4O provide you some objects that have been tagged with activationPurpose on there getter/setter : like :
com.db4o.collections.ActivatableArrayList
So every java collection that should be store must be replace with it db4o equivalent (com.db4o.collections.*).
Related
Good afternoon fellow developers,
I have come across a scenario where I found myself needing to retrieve the list of pending changes from my model and editing a specific property of those entries before sending them to my back-end.
These are new entities I created using the createEntry() method of the OData model v2. But, at the time of creation of said entities, I do not possess the value I need to add to them yet. This is the list of entities I retrieve by using the getPendingChanges() method on my model:
What I need to do is to loop through each of these newly created entities and set a specific property into them before actually sending them to my back-end with the submitChanges() method. Bare in mind that these are entry objects created by the createEntry() method and exist only in my front-end until I am able to submit them with success.
Any ideas that might point me in the right direction? I look forward to reading from you!
I was able to solve this issue in the following way:
var oPendingChanges = this.model.getPendingChanges();
var aPathsPendingChanges = $.map(oPendingChanges, function(value, index) { return [index];});
aPathsPendingChanges.forEach(sPath => oModel.setProperty("/" + sPath + "/PropertyX","valueFGO"));
The first two instructions retrieve the entire list of pendingChanges objects and then builds an array of paths to each individual entry. I then use that array of paths to loop through my list of pending changes and edit into the property I want in each iteration of the loop. Special thanks to the folks at answers.sap for the guidance!
I have iOS app that takes data from the server as json and then serializes them into objects of different types. Types can be complicated, can contain subtypes, can inherit, so there is no any limitations. Another thing that makes everything even more complicated is some of types are stored as AnyObject? and only in run time they are being serialized into real types accordingly to the specific rules. Something like that:
class A {
var typeName: String?
var b: AnyObject?
}
Then when it's serialized it can be done something like that:
if let someClass = NSClassFromString(typeName) as? SomeGenericType.Type{
b = someClass.init()
}
Also querying should be done on all the data. Currently I'm trying to store all of them locally, then load into memory and query there from the code. I'm using User defaults, but they have some limitations, also I needed to provide custom coding to make it work, and each time when I add a new field it turned out that I missed something in coding and nothing works. So it's pain.
Ideally I would just do some magic command and all the objects are sent to local storage no matter how complicated they are. The same to extract them from this storage. Also, user change data so I can't just store primary Json. And I don't want to covert objects back to Jason as for it's pain too.
Any suggestions?
If you want to use sqlite then You can store whole object in one row! I means you can create table with 2 columns one is id and second is your dataobject(it's data type should be blob). Then convert your whole object into data. Then store in sqlite table and retrieve it as data then convert it to object when want to use. By this way your object will remains in same format as you asked
Firebase while meant for online synching and storage can also cache everything locally in case you are offline and perform query's against the local cache. It uses JSON.
CouchDB also has a mobile version for iOS.
Both of those are over kill if your dataset is small; you can just store it as a text file and read the JSON back in. See performance characteristics here. The graph is for a 7MB file so if you are significantly less than that your load time may be minimal.
NSKeyedArchiver.archivedData(withRootObject:) is great for storing custom objects as Data objects. The only thing you need to do to be able to use this is to make your custom objects conform to NSCoding. A great example can be found here:
Save custom objects into NSUserDefaults
Once you have the Data version of the object, it can easily be stored in UserDefaults, as a property in CoreData, or even in the app's keychain entries. Depending on your use case, sensitivity of data, and how much data you intend to store, you might want to use any number of storage methods. NSKeyedArchiver.archivedData(withRootObject:) allows you to pretty much use any of them.
I'm sorry the title may mislead you, since I'm not so good at English. Let me describe my problem as below (You may skip to the TL;DR version at the bottom of this question).
In Coredata, I design a Product entity. In app, I download products from a server. It return JSON string, I defragment it then save to CoreData.
After sometimes has passed, I search a product from that server again, having some interaction with server. Now, I call the online product XProduct. This product may not exist in CoreData, and I also don't want to save it to CoreData since it may not belong to this system (it come from other warehouse, not my current warehouse).
Assume this XProduct has the same properties as Product, but not belong to CoreData, the developer from before has designed another Object, the XProduct, and copy everything (the code) from Product. Wow. The another difference between these two is, XProduct has some method to interact with server, like: - (void)updateStock:(NSInteger)qty;
Now, I want to upgrade the Product properties, I'll have to update the XProduct also. And I have to use these two separately, like:
id product = anArrayContainsProducts[indexPath.row];
if ([product isKindOfClass:[XProduct class]] {
// Some stuff with the xproduct
}
else {
// Probably the same display to the cell.
}
TL;DR
Basically, I want to create a scenario like this:
Get data from server.
Check existed in CoreData.
2 == true => add to array (also may update some data from server).
2 == false => create object (contains same structure as NSManagedObject from JSON dictionary => add to array.
The object created in step 4 will never exist in CoreData.
Questions
How can I create an NSManagedObject without having it add to NSMangedObjectContext and make sure the app would run fine?
If 1 is not encouragement, please suggest me a better approach to this. I really don't like to duplicate so many codes like that.
Update
I was thinking about inheritance (XProduct : Product) but it still make XProduct the subclass of NSManagedObject, so I don't think that is a good approach.
There are a couple of possibilities that might work.
One is just to create the managed objects but not insert them into a context. When you create a managed object, the context argument is allowed to be nil. For example, calling insertNewObjectForEntityForName(_:inManagedObjectContext:) with no context. That gives you an instance of the managed object that's not going to be saved. They have the same lifetime as any other object.
Another is to use a second Core Data stack for these objects, with an in-memory persistent store. If you use NSInMemoryStoreType when adding the persistent store (instead of NSSQLiteStoreType), you get a complete, working Core Data stack. Except that when you save changes, they only get saved in memory. It's not really persistent, since it disappears when the app exits, but aside from that it's exactly the same as any other Core Data stack.
I'd probably use the second approach, especially if these objects have any relationships, but either should work.
I'll ask in the form of a hypothetical, which might make it easier for me to explain.
I have a class called Person, and in this has three fields:
NSString *name;
NSDate *dateOfBirth; and
NSMutableArray *friends.
An example object is this:
name = "John Smith"
dateOfBirth = 01/04/1985
friends = "Simon Scott"; "Jennifer Lane"; "Mary Firth"
Once the user has filled the NSMutableArray with the data they want, what would be the best way to save this data to the iPhone? I would anticipate that there could be up to 100 instances of the Person object, and all that will be required is the displaying of this data in a UITableView and giving the user the ability to add and remove entries at their will.
I have seen multiple suggestions on this site, which include NSDictionaries and using the writeToFile method, but before I research one of these, I was hoping someone could point me in the right direction? I would like to ensure that I'll be using the easiest and most appropriate method that's out there.
Many thanks.
Please take a look at the Property List Programming Guide. As long as you stick with a core set of object types for your data, you can write and read your data from a file or URL in one line, like this:
[people writeToURL:someURL atomically:NO];
The types you've mentioned in your question (strings, dates, arrays, dictionaries) can all be written to a property list.
#Achiral,
It really depends on what you want to do with the data and how concerned you are with the flexibility of your code.
However, my recommendation would be to use CoreData to make an SQLlite database and make a 'Person' entity with the properties that you list above. I don't know if you are familiar with CoreData, but it is highly optimized on iOS and is pretty easy to use, since it has a pretty simple 'fill in the blanks' style form for creating the data models. You should also note that CoreData is a well accepted and supported way to store data in an iOS and OS X app.
I hope this helps.
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").