I have been through a couple of these answers here, but I don't think I get it right..
I have several NSArray made of JSON requests. I want to store everything in the app instead of requesting the data all the time, and I understand I should use Core Data for this.
The problem is, I don't know how to initialize this.. I have tried to read up, but I have realized it will take a long time to understand this by just reading the class reference etc.
I have added an .xcdatamodel and created an entity with attributes identical to the data in one of the json object. How can I access the file for extracting and inserting information? I plan on parsing my whole json object into this file, but how can I instantiate the entity? Which delegates and where?
All tutorials I have watched had an option when they created the project, like "Use Core Data" or something, which when checked created lots of code automatically. I don't have that..
You might wanna go through some SO links: here. Also, I once remember going through this guide for adding Core Data to my project. It might help you to go through this link for saving JSON to Core Data directly. I recommended this link here in SO a couple of times. Trust me, all this pain you are enduring setting up Core Data is well worth it when you see things starting to work!
You need to add the core data stack. You can create a new, core data project, and get the core data elements added to the app delegate specifically for core data. You will have 3 properties, and one method. Just copy/paste the declaration and implementation of these elements to your app delegate. Make sure the managedObjectModel method and the persistentStoreCoordinator method are using your actual model name.
To work with core data, you need to read the core data documentation:
http://developer.apple.com/library/mac/#documentation/cocoa/Conceptual/CoreData/cdProgrammingGuide.html
You will have to create entities to represent your data, the properties for the entities, and so fort. Get started with your project, read the documentation, and get started. You will have more questions which you will either ask or find here, but at least you got enough to get started.
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I'm working on a quite large app on iOS. Up until now, I've been using CoreData like this:
Have a class, that have methods like -(NSArray*)getAllEntries, or -(void)saveEntry:(Entry *)entry, and Entry has a few properties like strings, dictionaries, arrays of other objects that might or might not be saved in CoreData, etc. Mostly, I init Entry with its default ctor, and set values to properties by fetching values from the NSManagedObject by using valueForKey: I get from the CD store.
I started coding like this because at the time I was new to obj-c and I come from a C++/Java background.
Now, I'm working on a new module in the app and want to do everything the obj-c way.
As I understood, if making the Entry object a subclass of NSManagedObject, I could only init it using [NSEntityDescription insertNewObjectForEntityForName:#"Entries" inManagedObjectContext:context];, which means it would be tied to the entity? The thing is, that I might want to for example init that object from the data that I pull from the internet and I might not want to save it to the persistent store. Or, I might want to fetch the object out of the store, edit the values, but not save it to the store. Everything would be fine (probably), but as I understand, if I call the save method on the context which was used to instantiate the object, the object will be saved to the store that I didn't want to be saved.
So now I'm a little confused on how should I continue doing this. Is my old way of doing Core Data Ok, or should I use the subclass of NSManagedObject and use some tricks that I don't know of yet? And if the latter, what are those tricks?
Link answers are discouraged, but you really want to read Apple's extensive documentation on Core Data. Specifically, google for "Creating and Modifying Custom Managed Objects".
(Currently found at this link.)
I am currently working on the app that is going to use database to store items. The first thing that everybody say, when it comes to store data in iOS is Core Data.
But, after few days of looking through tutorials and docs, I have a big question.
Let me explain architecture a little bit more. So we have a backend, where you can add items, also, we have iOS and Android application. I am creating a Core Data model for our database.
What we want,is to check if there is update for database and download it. The problem is that we don't use JSON or XML, we are using the new sqlite file.
Since Core data creates three files for database, which are:
db.sqlite
db.sqlite-wal
db.sqlite-shm
Is core data able to replace "db.sqlite" with the new one, that is downloaded from server?
Thought the idea of replacing the database file instead of importing objects to it is very tempting it's highly discouraged to mess up with sqlite database created by CoreData. You should never touch it manually, when you do, you'll very likely end up with broken DB or messed up data.
So no, CoreDate is not able to replace underlaying sqlite file. You should instead import your data using CoreData stack, that's how it's designed. Creating JSON/XML service is the best way you can go.
BUT IN THEORY and in case you would be able to keep CD internal information stored in the db untouched, it should be possible to replace the sqlite file. If your database is read-only for users, it might work, but if users are able to create or modify records, forget about it right now.
First, you'd have to tear down all CoreData stacks (Managed Object Context, Persistent Store Coordinator, Managed Object Model) that might be using it before you replace it, replace the file and re-create CoreData stack(s).
db.sqlite is the main database file, the other two are temporary files, Write ahead log (wal) and Shared memory (smh), so you don't need these two.
Remember you never MUST NOT change the structure of the database, just data in it!!!
However, as stated in the beginning, I do not recommend this approach at all.
New to iOS development..
Basically what i'm trying to do is hard code data into my app using core data. Two different types will be stored, both strings: quotes and authors (There will be around 20 of each in the app). I have a button on my Storyboard as an IBaction that when clicked will populate a label with a new quote and author. My struggle right now is 1) finding out how to create this data and 2) how to fetch this data.
Every resource i'm finding online goes through tutorials on how to store data that a user typed in and then fetch it from a button. I'm trying to figure out how to store data without user input and then fetch it. Any help is appreciated. Sorry for asking what I am sure is a pretty simple question.
Unfortunately, though this would seem like a simple task, to my knowledge there is know "built-in" way to prepopulate CoreData. You can build up a core database and then copy it into an app, or possibly use a third party solution, though. Searching for "prepopulate coredata" here and on google should give you a start.
Here's a couple threads that might help:
Any way to pre populate core data?
iOS CoreData - prepopulate db with existing indexes
app scenario: on the UI, a button is tapped to get contact list from the server. the request goes to subproject which does the download and parsing and returns the result thru its delegate to the UI. so far everything works properly. lets say there is no internet connection and we cant have the contact list. to solve the problem, I want to cache the data in core data. if there is no internet, the cached data will be returned. now the question that bugs me, is it possible to create one data model and use it in subproject to save the data and in UI where data get pulled and edit from the same data model?
so basically i want to access core data from different subprojects and UI.
i couldnt find hints or tutorials regarding this issue. any ideas?
thanks in advance!
edit:
a project "b" that is added to the parent project "a". the project "b" is actually a static library.
if i let the library to do the saving and returning data to UI, wont it be inefficient to get all data from core data then send it to the UI?
i actually hope that there is a way to use same data model in both UI and the library.
i want prevent the UI to have huge load of data. its better to hace core data to handle that incl. memory mangement. i'm still reading some sources and trying to implement it on a test project.
I would argue that only the main project should deal with persistency, as than you can always decide to handle it differently — save it permanently or not, use core data or a home grown sql wrapper…. So it would be up the the delegate to decide what to do with more data.
But along with the delegate protocol you could decide to maintain different model protocols that define, what your models can hold. this would be independent to the implementation. The delegate now could return objects — no matter if core data models or not — to the delegator if this objects conforms to the protocols. The delegator in the sub module now could check for values on the server and/or in the cache.
Im new to objective-c and I've been reading up on singleton classes. I want to implement it into my logic but im not sure if its correct/possible/doable to do so, any advise would be appreciated.
At the moment i'm loading data from an xml feed, but i want to have control what data should be displayed based on which button is clicked. For example, buttonA would display IT news and buttonB would display celebrity news.
My thinking is to load the xml data into sqlite on application start in the background and display my buttons view at the same time using the singleton class. If the user pushes the button it will query the required table and display the content into a tableView.
Is this viable? If not, could you please advise whats the best way to go about this?
Thank you.
First of all you should reconsider organization of your data model. You've named sqlite on one hand and a global array on the other.
I would point you to Core Data to store your parsed data in a convenient way. Finally all you need is to query the Core Data db and fetch what you need. This would be more memory efficient than storing your data in a global array.
Have a look at Apple's Core Data tutorial or at this nice turorial: "superdb-core-data-app-with-sections"
To share a managed object context you can use a singleton. Have a look at this blog post, it provides a solution without a singleton by passing references of the managed object context down the relevant objects. It is created in the app delegate.