So I'm in the middle of planning a little web app that will require quite large amounts of data stored on a user level, in one case, the system would take a large object from a system level and make a "user specific" version, a user can have multiple ones of these. Simplest would be to compare it to a form stored in a google spreadsheet, where the user is expected to use the template spreadsheet, then change not only the answers but also the question.
Security wise I am quite OK
In the second case there is requirement to store multiple objects, size about 250k to maybe 3mb, once again on a user specific level, with a potential to move it to a system level so additional users can access it. As an example, say the user can upload pictures, but may not want to share all of them. However, a user may choose to "publish" a small number of them because they are happy with those specific pictures.
What design patterns should I consider using specifically around web apps where the user have decent amounts of data? For example, would it make most sense to use a single large database and have a table that keeps track of resources or create separate tables per user?
I have considered putting it all in a mongo database.
Your approach may be wrong.
If you want to store user based binary data and make it accessible for the user itself or the community, you would need a hierarchic structure like so:
userid1
pic1,pic2,pic3
userid2
pic4,pic5,pic6
community
pic7,pic8
You could then grant read permissions to "community" for all users, and permission for each user to its own directory.
Usually there is nothing wrong using a database to store binary files if you consider partitioning, role permissions and an applicable interface to access the data.
My suggestion is to use a binary repository like Artifactory.
It provides hierarchic structures, simple search queries using HTTP requests and has caching abilities for frequently queried objects.
I also think that http requests are a lot easier to use and also there is an abstraction layer to the data which is more secure.
Artifactory is free.
So I am working on an iOS search where I have to implement a keyword search. I have used a custom view controller with a Search Display Controller object embedded into it. What I want to do is be able to store the search terms somewhere when the search button is clicked. I have thought of two ways:
store them locally in the device and query them up whenever a search is performed
store them in the web app this iOS app is connected to and perform a GET request to the web app whenever a search is performed
The second one I know how to do but I have no idea how to do the first one.
SO how do I store the search terms locally? Also, what would be a better option? The first, the second, or another?
EDIT: A remote API holds the data I am querying. I want to mimic the google search app functionality, in which it stores maybe 10-20 keywords that are searched by the user.
Thanks in advance!
It's tough to recommend with more understanding of the data and usage. For example, number of keywords? keyword list static or grows? keywords shared? what are you searching - local or remote?
EDIT: You clarified 10 - 20 strings. In that case, consider something as simple as -[NSArray writeToFile:atomically:] and just persist in a file. If you read and write in NSArray, you can work on them very quickly in memory.
Original:
If you store locally and it's a growing dynamic set of keywords, I would recommend CoreData or Sqlite directly. Sqlite is a very fast efficient local DB. If you do sqlite, checkout fmdb on github. It's an objective-c wrapper.
Concerning the pros and cons:
Local storage will be faster - you won't have network latency. Especially if you want to do type ahead queries on key stroke. Keeping in memory is even faster.
Consider how much data you're storing. How many key words are there? Is it feasible to store on the device in a DB or a file?
Do you want the keywords to be shared from multiple users? In that case either storing on the server or a combination of storing on the server and syncing to the device is needed.
Do the keywords grow over time based on usage? In that case a local database is better.
I am creating a Questions and answers app for iphone which allows user to answer the questions displayed.
Currently I am invoking a web service to store the users answers. But I am slightly worried what if the web service goes down. I need to store the users answers locally and then invoke the web service when it is up and running.
How can I store the users answers when the web service is down. Is Sqllite a good option for this?
Please suggest.
Thanks,
Is Sqllite a good option for this?
Yes, SQLite is decidedly a good option. The other choice would be Core Data.
Use CoreData or SQLite on iPhone?
It depends on the complexity of your data model. I've looked into something like this recently and here is what I learnt. The most popular data storage methods in the iPhone are:
plist
Good for small quantities (hundreds of Ks) of hierarchical data.
Bad if relationships or queries are complex (since you have to write the code).
Very easy to learn.
Supports array, dict, string, data, date, integer, real, boolean elements.
You can store it as XML, which is editable and portable, or as binary files, which is faster.
Core Data
It's a object graph manager with searching and persistent functionality.
You need a good few hours of learning.
Easy to use once you set it up.
Better than a plist because it lets you manage object graphs, grow your object model, write queries, undo/redo, migrations to modified data models, memory management, and handle concurrent access.
Better than SQLite because:
The performance is similar and the speed of development is faster.
Creating objects is faster.
When the objects are in memory, executing queries doesn't require a search in the backend (which usually is either memory or SQLite).
SQLite
A database.
Better than Core Data when the operation doesn't require you to bring objects to memory. Example: update, delete, and select 1 (see if something exists).
It has full text search if you compile the extension.
Hardest to learn. Easier if you use a wrapper: FMDB, egodatabase.
If you can get away with a plist do that. If you see the amount of code you will have to write is too much work, then switch to Core Data. Only if you are an expert and absolutely need the performance use SQLite (unless, of course, you already know SQLite and not Core Data).
It should be, yes. I'd set up a Core Data based app with entities for Questions and Answers and set up relationships between them. Then just use NSFetchedResultsController or whatever you would like to gather and display the data
You have several options:
Sqlite
Core Data
Client-Side storage
If you wish to go the web based route, I'd take a quick look at Safari Client-Side Storage and Offline Applications Programming Guide.
Basically, you store a local copy of the database in memory so incase the web service is down, users can still use the app.
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.
I am currently working on a web service which is periodically polled. It does not store its state and is instantiated everytime it is queried. Essentially, it retrieves the state of other external entities e.g. databases and delivers it back to the requester.
Recently, the need to store state as arisen in that
There is the need to continously collect data from a particular source and store the bits that are important/relevant
There is the need to collect the aggregate of a particular data source over a period of time
I came up with the following idea:
My main concern here is the fact that I am using a static class (essentially a global) to share data between the two services. Is there a better way to doing this?
edit: Thanks for the responses thus far. Apologies for the vaguesness of this question: just trying to work out what is the best way to share data across different services and am unsure as to the specifics (i.e. what is required). The platform that I am developing on is the .NET framework and both services are simply WCF services hosted as a Windows service.
The database route sounds like the most conventional way to go - however I am reluctant to go down that path for now (mainly for deployment/setup issues; it introduces the need to create new tables, etc in addition to simply installing the software) for at this point the transfer of relatively small amounts of data. This may of course change in the future and going the database route might be the way to go at that point.
Is there any other way besides adding a database persistance layer?
If you need to collect and aggregate data, you might want to consider using a database between the two layers. Or have I misunderstood something?
You should consider enhancing your question with more requirements: pretty much all options are open here.
Sure - how about data binding? I don't have a lot of information to go on here - about your platform but most sufficiently advanced systems offer it in some form.
You could replace your static shared data with some database representation, with a caching layer (like memcached) between the database and the webservice, so that most of the time the data is available very quickly from the cache, but can be retrieved from the database as needed.
I appreciate that you want to keep the architecture simple. Depending on the magnitude of items you have to look up and there permanency, you might just consider leveraging your file system or a message queue. It sounds like you want a file system, because that sounds the least amount of impact to your design.
If you start dealing with tens of thousands of small files, your directories could get hard to navigate and slow to do file lookups on. I typically shoot for about 1000 - 10000 files per directory, and concoct a routine that can generate a path to the file depending on the file name pattern. Keeping the number of subdirectories even is important, some file systems have a limit on the number of subdirectories in a parent directory.