I am building a small application using ionic3. For the database, I am using FireStore. But in order to reduce the amount of data being transmitted over the network, I decided to "cache" some useful info in my localstorage. Now, my worry is, if there is another applicationon on the device also using LocalStorage, and by coincidence, it has same keys (for example a key members to keep list of members) as mine to store data, will it change data I access on my app?
Since LocalStorage use SQLite storage, it store data in a private directory binded to the app using it (and not a global directory).
So no, your data while not change in your app (but in your browser, if you use the same IP and port, it will consider it's the same app, so it will change your data).
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I wanna create a chatapp for my friend, and now remote serve I will use firestore and locally sqlite, but I realized it is default for firestore to save data offline, so my question is I have some data like message, or sending setting for the app, is it ok just to save them in firestore offline which seems automatically and no extra costs.
It depends on what you want or need.
If you want to use the offline persistance only for storing in case internet is not there at all. Firebase supports that out of the box. But you need to keep in mind to do you calls carefully. Because on a slow internet connection, if you tell the Firebase access to wait for the online behavior. It will not be using the local first and you might not be able to show the data. Check the question here
Also if you want to use the offline persistance from Firebase, be mindful that the data size has a default of 40 megabytes of limit. You might assign that by your self. You can check this link
BUT, if you want to have heavy data manipulations and have more control over your data SQLite is more suggested.
My opionion: I think Firebase Offline persistance would be enough for you, so go for it.
a question about local and remote storage of user data. Is there a best practices for the common situation where a user accesses data from an API and can favourite or otherwise personalise the data.
I have seen tutorials, e.g. a movie browsing app, where the use can make a list of favourite movies, where this personalised data is stored locally (e.g. in sqflite) and other tutorials where this data is stored remotely, eg. firebase. And firebase has an offline mode, so that data can be synced later. In that case, is it a common use case to set up local storage as well as cloud storage? Is there a common practice for this situation?
Thanks for any insights.
This is not specifically a Flutter question, more of a general app development question. It's very common to have both local and cloud "storage" but I wouldn't think of it that way. If you're interacting with an API backend I wouldn't consider it as the cloud storage for your app. Instead look at it as a different component within your applications overall architecture. You API/Backend component, this way it's not apart of your app instead it's something your app interacts with.
I assume you know the purpose of your API. Returns your data you want to see, keeps track of user profile information and other sensitive information.
When it comes to local storage I'd say the most common scenarios for local storage is results caching and storing information that the API requires on every session to make the user experience a bit better. See some examples below for both:
On instagram they store your "Feed watermark" which is a string value that is linked to a specific set of results so that when you open the app and request again they return that set of results, plus anything new - Local storage
They also "store locally" (better referred to as caching) a small set of your feeds from your posts, a list of user profiles that has stories on them and your DM's for instant and offline access. This way when the app loads up it has something to show while performing the action to get the new information. - Caching
They also store your login token, that never expires. - Local storage
tl;dr: Yes. If you need data on every session to use your API store that locally in a secure way and use that to interact with your "Cloud storage".
I have a web application in which registered users enter data in a few forms and then, when they log in at a later stage, they see forms populated with their data. Data is stored on Postgresql server of the same hosting provider of the web server.
I'd like to encrypted data stored on Postgresql to prevent them to be read by the hosting provider.
I don't think this is possible to do, because whenever is the encryption key kept, if the webserver has to access it in order to serve pages to users, then it can use it to decrypt data to read them. Anyway I preferred to ask just to be sure I'm not missing something.
You could encrypt every piece of data put into the database, but for most applications it would be impractical - slow and extremely inconvenient.
Much better option would be to use dm-crypt encrypted block device for PostgreSQL data directory. It would be transparent for a database, so all features would work fine.
But you'd have to save encryption key somewhere in the database server filesystem or your server won't start with no interaction. So malicious hosting provider can still access all your data. Even if you don't store the key in the filesystem and type it yourself while mounting a data volume, then the key would have to reside in server memory, so malicious hosting provider can still read it.
There's not much you can do - you have to trust your hosting provider somewhat. You can only make a malicious one's live a little bit harder.
Can people give me examples of why they would use coreData in an application?
I ask this because most apps are just clients to a central server where an API of some sort gives you the information you need.
In my case I'm writing a timesheet application for a web app which has an API and I'm debating if there is any value in replicating the data structure on my server in core data(Sqlite)
e.g
Project has many timesheets
employee has many timesheets
It seems to me that I can just connect to the API on every call for lists of projects or existing timesheets for example.
I realize for some kind of offline mode you could store locally in core data but this creates way more problems because you now have a big problem with syncing that data back to the web server when you get connection again.. e.g. the project selected for a timesheet no longer exists.
Can any experienced developer shed some light on there experiences on when core data is best practice approach?
EDIT
I realise of course there is value in storing local persistance but the key value of user defaults seems to cover most applications I can think of.
You shouldn't think of CoreData simply as an SQLite database. It's not JUST an SQLite database. Sure, SQLite is an option, but there are other options as well, such as in-memory and, as of iOS5, a whole slew of custom data stores. The biggest benefit with CoreData is persistence, obviously. But even if you are using an in-memory data store, you get the benefits of a very well structured object graph, and all of the heavy lifting with regards to pulling information out of or putting information into the data store is handled by CoreData for you, without you necessarily needing to concern yourself with what is backing that data store. Sure, today you don't care too much about persistence, so you could use an in-memory data store. What happens if tomorrow, or in a month, or a year, you decide to add a feature that would really benefit from persistence? With CoreData, you simply change or add a persistent data store, and all of your methods to get information out or in remain unchanged. The overhead for that sort of addition is minimal in comparison to if you were trying to access SQLite or some other data store directly. IMHO, that's the biggest benefit: abstraction. And, in essence, abstraction is one of the most powerful things behind OOP. Granted, building the Data Model just for in-memory storage could be overkill for your app, depending on how involved the app is. But, just as a side note, you may want to consider what is faster: Requesting information from your web service every time you want to perform some action, or requesting the information once, storing it in memory, and acting on that stored value for the remainder of the session. An in-memory data store wouldn't persistent beyond that particular session.
Additionally, with CoreData you get a lot of other great features like saving, fetching, and undo-redo.
There are basically two kinds of apps. Those that provide you with local functionality (games, professional applications, navigation systems...) and those that grant access to a remote service.
Your app seems to be in the second category. If you access remote services, your users will want to access new or real-time data (you don't want to read 2 week old Facebook posts) but in some cases, local caching makes sense (e.g. reading your mails when you're on the train with unstable network).
I assume that the value of accessing cached entries when not connected to a network is pretty low for your customers (internal or external) compared to the importance of accessing real-time-data. So local storage might be not necessary at all.
If you don't have hundreds of entries in your timetable, "normal" serialization (NSCoding-protocol) might be enough. If you only access some "dashboard-data", you will be able to get along with simple request/response-caching (NSURLCache can do a lot of things...).
Core Data does make more sense if you have complex data structures which should be synchronized with a server. This adds a lot of synchronization logic to your project as well as complexity from Core Data integration (concurrency, thread-safety, in-app-conflicts...).
If you want to create a "client"-app with a server driven user experience, local storage is not necessary at all so my suggestion is: Keep it as simple as possible unless there is a real need for offline storage.
It's ideal for if you want to store data locally on the phone.
Seriously though, if you can't see a need for it for your timesheet app, then don't worry about it and don't use it.
Solving the sync problems that you would have with an "offline" mode would be detailed in your design of your app. For example - don't allow projects to be deleted. Why would you? Wouldn't you want to go back in time and look at previous data for particular projects? Instead just have a marker on the project to show it as inactive and a date/time that it was made inactive. If the data that is being synced from the device is for that project and is before the date/time that it was marked as inactive, then it's fine to sync. Otherwise display a message and the user will have to sort it.
It depends purely on your application's design whether you need to store some data locally or not, if it is a real problem or a thin GUI client around your web service. Apart from "offline" mode the other reason to cache server data on client side might be to take traffic load from your server. Just think what does it mean for your server to send every time the whole timesheet data to the client, or just the changes. Yes, it means more implementation on both side, but in some cases it has serious advantages.
EDIT: example added
You have 1000 records per user in your timesheet application and one record is cca 1 kbyte. In this case every time a user starts your application, it has to fetch ~1Mbyte data from your server. If you cache the data locally, the server can tell you that let's say two records were updated since your last update, so you'll have to download only 2 kbyte. Now you should scale up this for several tens of thousands of user and you will immediately notice the difference of the server bandwidth and CPU usage.
I am developing an iPhone app which retrieves information via NSUrlRequest and displays through UIWebView.
I want to hold initial data (such as HTML pages, images) as a cache so that users of my app can access to data without network costs at the first time.
Then, if data on my web server are updated, I would download them and update the cache.
For performance issues, I think it is better to store data on file system than on core data.
Yet, I think it's not possible to release a new app writing data on disk.
So, I am about to store initial data(or initial cache) at Core Data, and when users launch my app for the first time, I would copy the data to disk (like /Library folder).
Is it, do you think, a good approach?
Or,...hmm, can I access to Core Data using NSUrlRequest?
One more question,
I might access to file system using NSURL, which is the same as to data on the Web. (right?)
My app would compare version of the cache with version of data on my web server, and if it's old, retrieve new data.
and my app will access only to file system.
All data are actually HTML pages including script, and images. And, I want to cache them.
could you suggest a better design?
Thank you.
Is it, do you think, a good approach? Or,...hmm, can I access to Core Data using NSUrlRequest?
No.
One more question, I might access to file system using NSURL, which is the same as to data on the Web. (right?) My app would compare version of the cache with version of data on my web server, and if it's old, retrieve new data. and my app will access only to file system. All data are actually HTML pages including script, and images. And, I want to cache them.
Yes.
But you could also be more clever. And by "more clever" I mean "Matt Gallagher." Take a look at his very interesting approach in Substituting local data for remote UIWebView requests.