I have a question regarding this topic.Like for Client Server Applications
1) is it necessary to load database directly into the Application.
Suppose if I have a DB in the back end and My application has to connect to that DB and display the results on the View for this do I need to Add DB into the Application directly.
2) can we access any DB or a File on the Remote server and show the required results.( with out adding that particular DB or A File into the application directly). How can we do this.
I saw a similar question in stackoverflow one answer was to use a PList, I am new to this.I am browsing the net but not able to get clear results. I lost many of my interviews because of this question.
Thanks,
1) is it necessary to load database
directly into the Application.
Suppose if I have a DB in the back end
and My application has to connect to
that DB and display the results on the
View for this do I need to Add DB into
the Application directly.
I'm not sure I understand this question. No, you don't need to load a database directly into a client in a client-server architecture. Normally, when I think of a design where a server has a database, I imagine there's some kind of way for the client to query the server for information. Perhaps it's making HTTP requests, which the server parses into a query, runs the query, and then returns the results (perhaps in XML form?).
2) can we access any DB or a File on
the Remote server and show the
required results.( with out adding
that particular DB or A File into the
application directly). How can we do
this.
Are you asking if it's possible, in general, to access a server database from a client? Yes, of course. (See above, re: HTTP Requests).
Any arbitrary file? That depends on how the server is set up. Again, HTTP is one protocol works that way; if you send an HTTP query like "GET someimage.png HTTP/1.0", the server could just be grabbing the whole file someimage.png and sending it back in the response. (Technically, it's not necessarily snarfing a whole file -- it could be creating that PNG dynamically since there's nothing in the HTTP protocol that says it must be sending an existing file -- but that's outside the scope of your question.)
I lost many of my interviews because
of this question.
Not to sound too snarky, but interviews are often won and lost not because you don't know the answer, but when you can't communicate effectively. You haven't phrased your question(s) here particularly well.
Related
Theres a ton of videos and websites trying to explain backend vs frontend, but unfortunately none of them explains it in a way that you know how to develop a backend - driven website (at least I haven't found anything good).
So, I wanted to ensure that I understood it and kindly ask you to confirm or correct me on this topic.
Example:
I wanted to build Mini - Google. I have a Database containing 1000 stored websites.
Assumption #1:
Everytime I type something into the search bar, the autofill suggestions change. This means, everytime i type, another website / API gets called returning the current autofill suggestions. On a developer site, this means the website e.g. is a Python script which gets called with the current word typed in as a Parameter and is returning all suggestions as e.g. JSON:
// Client Side Script
function ontype(input):
suggestions = get("https://api.googlemini.com/suggestions?q=" + str(input))
show(suggestions)
Assumption #2:
This also means I could manually call the website containing the Python script, providing a random word and it would always return a JSON containing the autofill suggestions for that word.
Question #1:
If A#1 turns out true but A#2 turns out false, how could I prevent a user from randomly accessing the "API" while still returning results when called by a script?
Assumption #3:
After pressing enter, my website googlemini.com/search?... would be called. As google.com/search reloads everytime searching for a new query (or going to page 2 etc.), I assume, instead of calling an API, when the server gets the client request, it first searches through its database, sorts the results and then returns a whole html as a static webpage:
// Server Side Script
#app.route("/search")
function oncall():
query = getparam("q")
results = searchdatabase(query)
html = buildhtml(results)
return html
Question #2:
Often, I hear (or at least understand it this way) that database and webserver are 2 seperate servers. How would that work? Wouldn't that mean the database server needs to be accessible to the web too (of course it would have security layers etc., but technically it would)? How could I access the database server from the webserver?
Question #3:
Are there, on a technical basis, any other ways to build backend services?
That's it. I would also appreciate any recommendations like videos, websites or others to learn how to technically setup and / or secure backend servers.
Thanks in advance.
For your first question you can yes there is a way to prevent miss use.
What you can do is add identifier to api like Auth token to identify a user and every time a user access the api you can save the count on the server n whenever the count has exceeded a limit within a time span you can reject the call. And the limit can be set in such a way that it doesn't trouble the honest user and punishes the wrong one. There are even more complex and effective methods but this is the basic idea.
For question number to let me explain you a simple concept a database is a very efficient, resourcefull and expensive data storage solution we never want it to be used in a general sense as varible store or something. We always want to access the database in call get the data process the data update the data. So we do it data way and its not necessary you make sepreate server for data base. The thing is we mostly make databse to be accessible to various platforms android, ios, windows. So its better to add some abstraction and keep data base as a separte entity.
For the last, I am not well aware about what you meant by other but I am listing some backend teechnologies, some of these might be used in isolation some of these not some other tools as well.
Django
FLask
Djnago rest
GraphQL
SQL
PHP
Node
Deno
Context
Greetings,
One day I randomly found RethinkDB and I was really fascinated by the whole real-time changes thing. In order to learn how to use this tool I quickly spinned up a container running RethinkDB and i started making a small project. I wanted to make something very simple therefore i thought about creating a service in which speakers can create room and the audience can ask questions. Other users can upvote questions in order to let the speaker know which one are the best. Obviously this project has a lot of realtime needs that i believe are best satisfied by using RethinkDB.
Design
I wanted to use a vary specific set of tools for this. The backend would be made in Laravel Lumen, the frontend in Vue.JS and the database of course would be RethinkDB.
The problem
RethinkDB as it seems is not designed to be exposed to the end user directly despite the fact that no security concern exists.
Assuming that the user only needs to see the questions and the upvoted in real time, no write permissions are needed and if a user changed the room ID nothing bad will happen since the rooms are all publicly accessible.
Therefore something is needed in order to await data updates and push it through a socket to the client (socket.io for example or pusher).
Given the fact that the backend is written in PHP i cannot tell Lumen to stay awake and wait for data updates. From what i have seen from the online tutorials a secondary system should be used that should listen for changes and then push them. (lets say a node.js service for example)
This is understandable however i strongly believe that this way of transferring the data to the user is inefficient and it defeats the purpose of RethinkDB.
If I have to send the action from the client's computer (user asks a question), save it to the database, have a script that listens for changes, then push the changes to socket.io and finally have the client (vue.js) act when a new event arrives, what is the point of having a real-time database in the first place?
I could avoid all this headache simply by having the Lumen app push the event directly to socket.io and user any other database system instead.
I really cant understand the point of all this. I am not experienced with no-sql databases by any means but i really want to experiment with them.
Thank you.
This is understandable however i strongly believe that this way of transferring the data to the user is inefficient and it defeats the purpose of RethinkDB.
RethinkDB has no built in mechanism to transfer data to end-users. It has no access control (in the conventional sense) as well. The common way, like you said, is to spin up one / multiple node instance(s) running socket.io. On each instance you can listen on your RethinkDB change streams and use socket.io's broadcast functionality. This would be a common way, but as RethinkDB's streams are pretty optimized, you could also open a change stream for every incoming socket.io connection.
I'm developing a project here and everytime I need to send a query to MYSQL I'm opening a new connection.
Is this right or should I only connect once? How should I proceed?
Thank you
Probably you should not open a new connection for every query.
There are exceptions to every general rule, of course, but typically you should connect once, sometime before the first query, and then re-use the same mysqli connection object for multiple queries during the given PHP request.
There is no limit to the number of queries you can run in serial using a given connection. The only limitation is that you can run only one query at a time.
Think of it this way: if you were writing a PHP script to simply read a file, and you knew you were going to read multiple lines from the file, you would keep the file handle open and make multiple read requests from it before you close the file. You would not re-open the file every time you wanted to read from it during a single PHP request.
The overhead of opening new connections to the database is reasonably low (at least for MySQL), but if you have an opportunity to easily reduce that overhead, it's likely worth it to do so.
Re your comment:
You're right, there's no way to keep your $mysqli object across pages. That's what is meant by the term request. Objects and resources are cleaned up at the end of a request.
When you said you were creating a new database connection for every query, I assume you meant that if you execute more than one SQL query during a single request (that is, page view), that you would create a new $mysqli object for each query. That would be unnecessary.
There's one other way you can reuse the database connections from one page view to the next. That is to use persistent connections. This doesn't preserve the $mysqli object -- you still have to run new mysqli on each page load. But internally it is reusing the database connection from a previous PHP request.
All you have to do to open a persistent connection in this way is to add the prefix p: to your hostname.
Servers and databases have a finite number of connections available. If every one of your users keeps an open connection for no reason (like when they are reading a blog post for a page that already loaded) then it will cap the number of people who can connect to your project in production. Unless there is a very specific need to keep a connection open, I recommend not doing so.
Again though, it really depends on the scope of your project. If you are just talking about a single page of a website, typically it's fine to leave the connection open until you are done loading the page.
I'm developing an application that needs to be syncronized with remote database. The database is connected to the a web-based application that user able to modify some records on the web page.(add/remove/modify) User also able to modify the same records in mobile application. So each side (server - client) must be keep the SAME latest records when an user press the sync button in mobile app. Communication between server and client is provided by Web Serives.(SOAP) and i am not able to change it because of it is strict requirements. (i know this is the worst way that can be used). And another requirement is the clients are not able to delete the server records.
I already be familiar with communicating web service (NSURLConnection), receiving data (NSData) and parsing it. But i could not figure out how the syncronization procedure should be. I have already read this answer which about how i can modify server and client sides with some extra attributes (last_updated_date and is_sync)
Then i could imagine to solve the issue like:
As a first step, client keeps try to modify the server records with sending unsyncronized ones. New recoords are directly added into DB but modified records shoud be compared depending on last_updated_date. At the end of this step, server has the latest data.
But the problem is how can manage to modify the records in mobile app. I thought it in a two way:
is the dummiest way that create a new MOC, download all records into this and change with existing one.
is the getting all modified records which are not in client side, import them into a new MOC and combine these two. But in this point i have some concerns like
There could be two items which are replicated (old version - updated version)
Deleted items could be still located in the main MOCs.
I have to connect multiple relationships among the MOCs. (the new record could have more than 4 relationships with old records)
So i guess you guys can help me to have another ideas which is the best ??
Syncing data is a non-trivial task.
There are several levels of synchronization. Based on your question I am guessing you just need to push changes back to a server. In that case I would suggest catching it during the -save: of the NSManagedObjectContext. Just before the -save: you can query the NSManagedObjectContext and ask it for what objects have been created, updated and deleted. From there you can build a query to post back to your web service.
Dealing with merges, however, is far more complicated and I suggest you deal with them on the server.
As for your relationship question; I suggest you open a second question for that so that there is no confusion.
Update
Once the server has finished the merge it pushes the new "truth" to the client. The client should take these updated records and merge them into its own changes. This merge is fairly simple:
Look for an existing record using a uniqueID.
If the record exists then update it.
If the record does not exist then create it.
Ignoring performance for the moment, this is fairly straight forward:
Set up a loop over the new data coming in.
Set up a NSPredicate to identify the record to be updated/created.
Run your fetch request.
If the record exists update it.
If it doesn't then create it.
Once you get this working with a full round trip then you can start looking at performance, etc. Step one is to get it to work :)
I have a task at hand to create a iphone app which is required to do the following.
the app should get the data entered by the user and store it into a remote server database.
other app user can see the data in the remote database.
store login information of the user using the app so as to keep track of what information as uploaded and by who
the thing that i would like to know.
1) What SQL server database is best to accomplish the task.
2) what format is best to retrieve the information from the database.
3) how to send the data from the iphone to the remover server database to it can store the data.
i read up on SQLite and found out that this particular database is a offline which stores the data locally so it cannot be viewed by other used. i wan to use a SQL database which can be accessed remotely.
1) What SQL server database is best to accomplish the task.
For implementation on server side, you can implement any server database, it does not matter. For implementation on iphone device, you have to implement SQLite database, which will provide storage locally.
2) what format is best to retrieve the information from the database.
You can retrieve data using XML or JSON format which will be parsed in device and can be stored in SQLite database, it is the easiest way to transfer data between client and server.
3) how to send the data from the iphone to the remover server database to it can store the data.
You can send data from iphone to server in XML/JSON format or by passing parameters in POST or GET request method then this format is parsed on server side and store data on server database.
For all this, you will require to implement API on server side, which will be the interface between server and device.
I know you mention SQL specifically, but is this a requirement or just a choice based on what most other people are doing? I ask because personally I would give serious thought to using a NoSQL database (document store) like couchdb for such a task. Deploying couch means you often don't need server side application layer at all, the way you will for a SQL based solution.
You talk to couch using HTTP which is perfectly suited to the ASIHTTPRequest library for example. Fetching data is usually a GET request and storing documents is done with PUT. All the data in or out comes back as JSON so a good JSON library will make life easier.
The combination of couchdb and the 2 libraries linked above, makes developing a data driven application really, really easy.
That's how I would do it ...
If you really need to stick with SQL, then as Jignesh says, use whatever database you like and implement a suitable API in the server side language of your choice. You can transfer the data however you like although JSON would still get my vote as a relatively light protocol that remains human readable.
You can use a cloud-enabled database service, like windows azure.