There are several apps that I use on my Mac that store their data in core data. I can see the data I want in CoreDataPro. I want that data - specifically I want to send changes in that to some remote end points (such as Zapier, or some other REST service).
I was thinking of piggybacking something like RestKit - such that I provide a configuration file saying where the app is and what end points the data needs sending to. I need only to scrape the data and send to REST, not a two-way sync.
I'd prefer a utility that I could configure rather than having to code a Mac application.
I noted http://nshipster.com/core-data-libraries-and-utilities/ - RestKit still seemed the most capable, but in https://github.com/RestKit/RestKit/issues/1748 I was advised that coredata projects should only be opened by a single application at a time, and really RestKit is designed for baking into the source app (rather than for database scraping and sending).
What approach would you take?
I also noted:
http://www.raywenderlich.com/15916/how-to-synchronize-core-data-with-a-web-service-part-1
Thanks, Martin.
First, Core Data is an object store in memory. What is written to disk from Core Data can be in one of several formats. One of those formats happens to be SQLite. If the application is writing to SQLite then it is possible to sample that same file and push it somewhere else.
However, each application will have its own data structure so you would need to be flexible in the structure you are handling.
RestKit has no value in this situation as you are just translating objects into JSON and pushing them to a server. The built in frameworks do that just fine.
There is no utility to do this at this time. You would need to write it yourself or hire someone to write it.
If I were going to do something like this, I would write it using Core Data itself interrogate the model from the application that wrote the data in the first place and then translate the database into JSON and push it. You won't be able to tell what is new vs. old so the server will need to sort that out.
Another option, since you can't diff anyway, is to just push the sqlite file to the server and let the server parse through it.
Other answers might include:
use a middleware platform e.g. using rssbus.com (only) sqlite connections are free to send the events
as my target system (http://easy-insight.com) actually has a transmitter that sends new records it sees from MySQL abd PostgreSQL, I could https://dba.stackexchange.com/questions/2510/tools-to-migrate-from-sqlite-to-postgresql or use an ETL such as http://www.easyfrom.net (I did ask the vendor for SQLite support a long time ago, but SQLite is just not a priority for them).
I'm wondering whether a good answer (where good excludes Objective-C and includes languages that I do know, such as - to a limited extent - Ruby) is to use MacRuby and its Core Data libraries.
Core Data seemingly can be exposed as an Active Record. https://www.google.com/search?q=macruby+coredata , notably http://www.spacevatican.org/2012/1/26/seeding-coredata-databases-with-ruby/
However, MacRuby seems to have faded - https://github.com/MacRuby/MacRuby/issues/231 - it won't even compile on Mavericks.
I'm developing an iPad app, which is connected to a Django Server on the backend. The server mostly is just a REST API on top of a database (this is done with TastyPi, for the record).
I'm trying to understand the best way to develop this, since I'm new to iOS.
So a few related questions:
Is there a library that simplifies the work of making "models" in your code that mirror the models on the server?
I would imagine something like Django's ORM, which allows you to define objects in Objective C , that are mapped 1-to-1 to objects that the REST Api gives you.
This library could abstract all of the cache-ing and converting between local objects and the objects on the server.
If this kind of library doesn't exist, are there a set of best-practices for this type of project? For example, should I even have local objects that reflect the DB? Should I have one class which takes care of all the code that deals with the API, or should I write the requests in the many different objects that are part of the API?
In short, where can I learn the "right" way to code iOS apps backed by a REST Api exposing a database? Preferably a tutorial, rather than looking at existing projects' code.
1) For ORM, iOS has Core Data that lets you build your entity and work with objects rather than SQL statements like SELECT, LEFT JOIN etc.
Don't know about others, but this is how I usually do it:
1) App makes a HTTP POST request to the Web Service using a library like ASIHttpRequest library. (Note, for the backend, I wrote my web service using Symfony web framework)
2) The app sends back the JSON response.
e.g.
{
data
{
name: bob
age: 20
}
}
3) Parse the JSON using a JSON parser like JSONKit or the one provided by ASIHttpRequest and convert the JSON server response into a NSDictionary.
NSDictionary *data = [[request responseString] objectFromJSONString];
4) Now whether to store the data on the app or not depends on the nature of the app. If the app is to do searches for local restaurants, then you probably don't want to keep a local copy of the returned result, since the nature of the app is to search for restaurants.
However, if you got like a login system that downloads user's home work from their account, then you would likely store these data on the device locally.
This is where Core Data comes in, you build your model that replicates the server model and you do a simple 1 to 1 mapping between server and client models.
Hope that helps.
Check out Rest kit
RestKit is an Objective-C framework for iOS that aims to make
interacting with RESTful web services simple, fast and fun. It
combines a clean, simple HTTP request/response API with a powerful
object mapping system that reduces the amount of code you need to
write to get stuff done.
It also supports persisting remotely loaded objects directly back into a local store
The Parse.com api is RESTful, and takes care of a kajillion hours of boilerplate code construction for a database. I don't work for them, but I do like the service.
For #1, helios.io does the trick. From the docs at github,
In order to keep your data model and REST webservices in sync, you can link it to your helios application:
$ helios link path/to/DataModel.xcdatamodel
This creates a hard link between the data model file in your Xcode and Helios projects—any changes made to either file will affect both. The next time you start the server, Helios will automatically migrate the database to create tables and insert columns to accomodate any new entities or attribute
I'm trying to find some reading materials on how to connect an IPHONE app to a central DB-Server such as SQL-Server.
I know about SQLite, and the other methods of storing Data in the device itself. What I'm really interested is for the application to interact with a central database server. Are there any sort of objects such as SQLClient in .net or do I need to go through sending off HTTP-Requests and deserializing json/xml?
i dont know the answer to your question, but even if you find that it would be not recommended to do so, since its always better to use an httprequest solution,
Encapsulating the database implementation is always the way to go, since database implementation could change rather quickly adding a layer over it is recommended
That goes without saying that you will not be able to do caching by accessing the database directly, which is also a drawback
am sorry this is not the answer you are looking for, but you should re think on how you are going to implement your solution,
Preform a httprequest to a php script or similar and parse JSON or XML.
You would have to make a REST interface to bridge the 2 together, and as you said deserialize responses depending on the format, if it's json or xml.
From Device side, make GET/POST requests to your script, which responds the query results back to the app and handle them accordingly.
I'm about to start an iOS project that requires pulling user's data from an SQL Database and viewing it within the App. Before I begin I'm looking for conformation that I'm taking the right (best) route.
My Plan:
App starts on login page (app will display data from another service)
App uses AFNetworking to post request to web service
Web service gets user data from SQL Database and sends back JSON
App uses JSONKit to parse the feed and load into Core-Data
App uses info from core-data to populate UI
Does this seem like an appropriate way to get the info into Core-Data from SQL? Any suggestions for doing things differently?
Thanks.
Are you receiving the response from the web server in JSON? If so, the fact that the server is using an SQL database is immaterial. What you need to know is how to parse JSON for inclusion in a core data store. Cocoa is my Girlfriend has a pretty good tutorial up.
Part 1
Part 2
To answer your comment, here's what I've done.
Display a login screen. The login credentials should be stored in the keychain for security. I've used SSKeychain for this.
To handle sending and receiving data from a web request your best option is to use a pre-built library. I've always used ASIHTTPRequest, but since it is no longer under active development, you should probably look around a bit before you commit to anything. I'm sure there are nicer and cleaner libraries out there.
You need to parse the JSON responses. I'm a fan of JSONKit. It's very fast, very easy to use, very robust.
Pulling data out of the core data store and displaying it in the interface will be no problem for you. If you create a new project in Xcode most of the setup will be done for you.
Now, there are a lot of projects out there that attempt to combine web requests, json parsing and core data loading into one framework. I've tried to use a few of these and haven't had much luck. The ones I've tried haven't been robust and very difficult to debug. Setting up your own request/parse/load code is not difficult at all, just a bit time consuming.
I am sure that there are a lot os ways to make implement this problem. Your solution is one of the popular solutions I guess but you could connect to the DB via a socket and talk with the database directly e.g. Going over a port 80 web site has the advantage that the possibility of some kind of firewall blocking the communication is very low. I would solve this kind of problem the same way I guess.
I'm planning my first iPhone app and I'd like to get some inputs as to how to build it, right from the start. The iPhone app is being built to be paired with a public facing web application that is already built in PHP.
I'd like the web platform to be central (data is housed in a mySQL database), and have the
iPhone clients talk to it and use REST'ful methods to perform the functions of the site
(fetching latest content, posting content, voting, account management as examples).
I'd like the clients to get a local copy of the data in a SQLite database, but refresh to get the latest version of the feed (similar to the Twitter app).
Couple of thoughts I have right now:
Use something like ASIHTTPRequest to send/recieve data to PHP files on the server listening for requests
JSON - would I be better off to send the GET/POSTS to a PHP that returns JSON objects, and work with some sort of wrapper that manages the data and communicates changes to the local SQLite database?
Am I totally off in how I should be building this thing to communicate with the web? Is
there a best practice for this?
I'd really appreciate any input on how you would architect this sort of a setup.
Thank you,
EDIT: After reading my own post again, I know it sounds like a Twitter client, but it is NOT, although it has similar features/structure of a Twitter type setup. Thanks!
As you already outlined in your plan, XML and REST are a great way to communicate with a web application. I want to suggest few details about how to actually design and build it, or what you should keep in mind.
First of all, I believe it's important to stick with MVC. I've seen people creating HTTP connections in view-controllers, controllers being NSXMLParser's delegate, controllers containing data in member variables. I've even seen UITableCells establishing HTTP connections. Don't do it!
Your model and its basic manipulation code should be as much extracted from user interface as possible. As you already have created the model in your web-application, try to recreate the entities in your iPhone project. Don't be afraid of having some simple methods in entity classes, but do not make them use external resources, especially tcp connections. As an example of methods in entity class you might have methods that formats data in specific ways (dates as an example, or returning fullname as concatenation of firstname and surname), or you can even have a method like - (void)update that would act as a wrapper to call class responsible to update the model.
Create another class for updating the model - fetching the XMLs from web-app. Do not even consider using synchronous connections, not even from a dedicated thread. Asynchronous connections with delegate is the way to go. Sometimes multiple requests need to be made to get all required data. You might want to create some kind of state-machine to keep the information about in which stage of downloading you are, and progress from stage to stage, skipping to the end if error occurs, re-executing from failed stage after some moments.
Download data somewhere temporarily, and first when you have it all, make a switch and update user interface. This helps responsiveness during launching the app - user gets to work immediately with data stored locally, while the update mechanism is downloading the new data.
If you need to download lots of files, try to download them simultaneously, if dependencies between files allow for that. This involves creating a connection per request, probably delegate instance for each of them. You can of course have only one delegate instance for all of those connections, but it gets a bit more complex to track the data. Downloading simultaneously might decrease latency considerably, making the mechanism much faster for the user.
To save the time and bandwidth, consider using HTTP's If-Modified-Since and/or ETag headers. Remember the time or tag when you requested the data the last time, and next time send it in HTTP's header. Your web-application should return HTTP code 304 if content has not been changed. iPhone app should react on this code accordingly in connection:didReceiveResponse:.
Create a dedicated class to parse the XML and update the model. You can use NSXMLParser, but if your files are not huge I strongly recommend TouchXML, it's such a pleasure to work with XML as document (it also supports XPath), instead of an event based API. You can use this parser also when files are downloaded to check their validity - re-download if parsing fails. That's when dedicated class for parsing comes handy.
If your dataset is not huge, if you do not need to persist downloaded data on iPhone forever, you probably don't need to store them in SQLite database, you can simply store them in XML format - just a simple caching. That at least might be the way for a twitter app. It gets easier that way, but for bigger data sets XML consumes lots of memory and processing power - in that case SQLite is better.
I'd suggest using Core Data, but you mention this is your first iPhone app, so I suggest you don't use it. Yet.
Do not forget about multitasking - your app can go to sleep in the middle of download, you need to cancel connections, and cleanup your update mechanisms. On app's wake-up you might want to resume the update.
Regarding the view part of the application - use Interface Builder. It might be painful in the beginning, but it pays off in the long run.
View controllers are the glue between model and views. Do not store data in there. Think twice about what to implement where, and who should call it.
This is not related to architecture of the app, but I want to remind that Objective-C is very expressive language. Code should read much like a sentence. Extend classes with protocols. As an example the other day I needed first line of a string. Sure, you can write a one-liner where you find first occurrence of a new-line, and get a substring from beginning till there. But it doesn't look right. I've added - (NSString*)firstLine into my NSString's protocol. Code looks so much better this way, it doesn't need any comments.
There are lots of things to consider in both architecture and design of any project, they both should go hand in hand. If one is causing trouble to the other, you need to adapt. Nothing is written in stone.
I'm currently working on an app that sounds similar to yours. I'd also suggest ASIHTTPRequest, and probably something like TouchJSON for JSON parsing, or extending/making a delegate of NSXMLParser if you want to parse XML.
As suggested by JosephH, depending on how your app works you may want to consider alternate authentication methods: I'd take a look at something token-based like OAuth, which has ready-made libraries for people to dig in to.
SQLite is totally viable for feed caching, although I prefer NSCoding so that you can freeze-dry your custom data structures.
As a general suggestion, make sure to spend a lot of time thinking about every use case and corner case for connections: it's easy to assume a user will only contact the server in certain ways and at certain times, and then after you throw in multitasking/incoming calls/lock screen/memory warnings, things can get hairy without any planning.
All in all, you seem to be on the right track, just make sure you plan out everything beforehand :)
Apple have a brand new in depth piece of sample code - MVCNetworking that shows in depth how to use subclasses of NSHTTPRequests and NSOperationQueues.
As others mentioned, I think you are asking the right questions and are heading in the right direction. All of the replies above are valuable advice. Here is my advice, and I hope you'll find it useful.
No matter which method/library you choose to talk to your web services, I think it's important to make a clean separation in the way you design your data model on the phone VS. the data model in your web application. You have 3 major distinctions to keep in mind for your design:
Data model on the web application (reflected by your existing mySQL database)
Since this is already there, there is not much to say about it, except that it will influence a lot your design for the following 2 parts. I suggest to make this model the 'master reference' for how your data is represented across platforms.
Data model on the iPhone app (reflected by the information you need to display in the iPhone app)
This is where the fun begins. First, you need a good understanding of what data you need to display in the phone app. So have a good, high level design of your app first (use pen and paper, draw mock-ups of each view and the interactions between them, model the navigation between your view controllers etc.). It really helps to understand the interactions between your view controllers and the various bits and pieces of data you want to show in the app. This will help you create the requirements for the data model on the phone. Based on these requirements, map the existing (web) data model to a new model, suited to your iPhone app. This new model may or may not include all tables and fields found in your web app. But the general representation of the 2 models should be very similar (e.g. relationships, data types, etc.)
Data model used to communicate between the 2 above (this is your 'data exchange protocol')
Once you have the 2 representations of your data above, you need to 'translate' from one to the other, both ways. Design your data exchange protocol to be as simple and compact as possible. You don't want to waste bytes on useless information, as transmissions over the network are costly. (As a side note, you might think of compressing the transmitted data later on, but it's just as important to have a good design from the beginning). It's probably best to begin with a protocol in which the metadata is the same as the one in your web application model (e.g. same relationships, names of tables, attributes, etc.). But remember, you'll only have to serialize/de-serialize those entities and relationships that you listed in point 2) above. So design accordingly. Your exchange protocol may also include session tokens, authentication info, a version number, or other metadata, if you need it.
Remember: your data exchange protocol is what will de-couple your web application and iPhone application models. I found that it's best to de-couple them because they may both evolve over time. The data model on the iPhone for example, may evolve a lot especially when you will find that you need to re-model some relationships or add/remove attributes from your entities in order to improve application responsiveness, or the user experience, the navigation, or whatever.
Since this is a whole concern in and by itself, well, you need to design a generic serialization/de-serialization mechanism on top of your (JSON/XML/whatever parser you choose) that is flexible enough to sustain the potential differences between your 2 data models. These differences might be: entity/attribute/relationship names, primary key identifier names, data types, attributes to ignore, and the list goes on. I would definitely implement a serializer/de-serializer utility class in the iPhone app, backed by a .plist configuration file containing all supported entities, concerns, aliases you might have. Of course, each model object should 'know' how to serialize, de-serialize itself and its relationships (i.e. the required object graph depth).
One last note, since you will end up with 2 representations of your data, you will need a way to uniquely identify an object on both sides. So for example, think of adding a uuid attribute to all data that needs to be exchanged, or use any other approach that suits your needs.
I am building an app that has similar requirements to yours, and these are the approaches I found to be best so far. Also, you might find this video useful (it inspired me a lot on how to implement some of the issues I mentioned above and is especially interesting if you're using CoreData) :
http://itunes.apple.com/ca/podcast/linkedin-important-life-lessons/id384233225?i=85092597
(see the lecture entitled "LinkedIn: Important Life Lessons on CoreData & GameKit (March 12, 2010)" )
Good luck!
It's quite a broad question, and I think you're going in the right way anyway, however I'll do my best to give some advice:
JSON, ASIHTTPRequest and POSTs to PHP scripts sound like a great way to go.
If the data is not really sensitive, I'd use http most of the time, and use https only for a login page that either sets a cookie or returns a "token" that you use in subsequent requests. (HTTPS can be quite slow over a 3G connection as the overhead in terms of number of packets to setup an SSL connection is higher than a plain TCP connection.)
You should make sure you correctly pass any data from the input to the PHP scripts to the database, to avoid any SQL injection attacks - ie. used parameterised SQL, don't create sql queries by doing "SELECT * from users where username="+$_GET['username']"
I would do this like I have done with a lot of AJAX web-page stuff. i.e.:
Have a URL on your server side package the information to be transmitted into XML format. (This can be through a CGI/PHP script or whatever). Your transmitting XML in the message body - so it's easy to human read and debug with a standard web browser.
Use the standard iPhone NSXMLParser methods to parse out the individual data fields from the XML doc, and write it back to your database. This method is equiped to both fetch the data from a URL and parse it in one call - like:
NSURL *xmlURL = [NSURL URLWithString:#"http://www.example.com/livefeed.cgi"];
NSXMLParser *myParser = [[NSXMLParser alloc] initWithContentsOfURL:xmlURL];
Walk through the data hierarchy with the NSXMLParser methods and populate your database accordingly.