This is basically a simple question, but I haven't found a good answer here or with Google.
We have a Ruby on Rails app with a form that needs to update a section when the user changes the selected option in a pulldown menu. The complication is that this update will be from the database - it can't realistically store and hide all the possible data when it loads. The obvious solution is an Ajax call, but the problem is that Ajax is asynchronous, and our update is inherently synchronous. We need to ensure that the user gets the updated info before submitting or doing any other work on the form.
I know one can (but shouldn't) specify that an Ajax call be synchronous, but is there a better approach to this? I hate to do a separate post and reload every time the user selects a different option in one field, but I'm not sure what the best practice is for a situation like this.
Update: I tried switching to using an XMLHttpRequest object in JavaScript, and it may work (I'm figthing with Rails routing issues right now), but it gives me a warning that the synchronous option for this object is deprecated. Is there really no accepted way to get synchronous communication between a web page and server?
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Short version: Is there a callback when the rails view is finished rendering?
Longer explanation of my actual problem:
I have this issue where I want to generate a history-object because of some APIs I'm using. So I will be appending to this history object possibly several times before saving it. I know that I can safely save it when the view is rendered, because then there will not be any more calls to the APIs.
After quite a while of googling I can still not find any way of doing this. Is my intended approach the right one, to get a callback from the renderer that says "now everything is rendered. Go ahead and save", or should I do it in a different way?
Does such a callback even exist, or do I need to make it myself?
I would lean towards suggesting that you shouldn't be leaving functionality until after the page has rendered - you should really have completed any API calls in the controller before you start outputting the page. However, if you really must do this you can use javascript to fire off a function (such as an ajax request to an action) after a page has finished rendering.
http://api.jquery.com/ready/ should give you a good starting point!
I have a Rails Application where I want to present user with a sequence of Questions in a particular order. A user cannot proceed to the next question unless he has answered the previous one.
Here are some design issues I need help on for an efficient implementation:
To fetch a list of questions for a user I need to make an expensive
db call. Once for a new session, the list if fetched I simply want the
user to see the questions in a particular order starting from the
first question. If the user had attempted some questions in
a pervious session he will jump to the question he last left off. How
to implement it efficiently? I believe I need caching here.
On rendering the views :
How to render the view for this feature? I can have a controller with
the initial question template. When user attempts the question, should
I have question-answer options text updating with AJAX? Do I have to
use jquery for the purpose or any Rails helper could be of help here?
Any design help, rails features-gems I could make use of will be welcomed.
My answer is not specific to Ruby on Rails, but it should still work.
First I wouldn't load data that you potentially won't use in advance. If you have 10 questions, and you only show one at a time, then I would just load the first and then once the user has finished the first, go ahead and load the second. No need to load all ten because maybe the user never makes it to question 10.
Assuming the user leaves pre-maturely, you can just make an AJAX call to pick up where you left off.
I would agree that you should cache those questions though.
The steps would look like this then:
First question - loaded via AJAX. Answer and progress saved via AJAX call.
If (1), then second question loaded via AJAX. Answer and progress saved via AJAX call.
Repeat until questions done.
This way you can use user/login information to make an AJAX call to pick up where you left off. I would imagine this would make your database calls much less expensive.
I have a rails app that shows users posts. Users posts can be sorted in many ways, paginated, categorized, etc. I am doing all of these clicks over ajax.
However, everytime I click a category or a sortby param or a new page, it loads the ENTIRE request again and then returns it in the way specified. Is there any way to cache my first results and THEN sort, paginate, categorize quickly?
In order to enhance the performance, a better way is to use memcache. If you have memcache installed and implemented in your rails app, you can cache that query for a certain period of time without actually querying the database again instead it will fetch directly from memory again, thus it improved performance greatly. You may want to check out https://github.com/nkallen/cache-money.
This is a question of using AJAX vs a non-AJAX javascript implementation.
When using Ajax, the question you should ask yourself is, does this action require more information or logic from the server? If the answer is no and you can do it using only the information you have already loaded on the client browser, you should try and implement it using Javascript.
In this case, there are plenty of solutions for javascript sorting out there. For example, if you want a simple table-like sorting (your table could be invisible) you could use something like this plugin: http://yoast.com/articles/sortable-table/
If you're looking for a more custom solution, you could write the javascript by hand, this post: Sort <div> elements using jQuery gives a good starting point.
Hope that helps!
I have a pretty extensive form on one of my rails sites and I was wondering if its possible to dynamically save the form for every onchange input. What I'm trying to prevent is users taking the time to fill the form out and then lose all their changes because of a connectivity issue or something stupid like that...
Any suggestions? Basically, I don't want the form to have to be submitted at all. I just want the form to save like a preference would in an Mac OS X (no apply or save button it just saves).
using rails 3...thanks!
The strain that would put on your server and DB would be several orders of magnitude higher than a more traditional approach. I also agree with Kyle that I would be very confused about the lack of submit button. At the very least, you'll need to notify users each time data is sent to the server and saved successfully, otherwise they'll have no idea why you aren't asking them to save.
Also, think about all the overhead. With every keystroke the user will have to initiate a connection, send their HTTP headers, cookies, the contents of the form, etc.
Have you considered an autosave feature instead? Maybe save the form every 2 minutes if changes have been made, and then put a submit button on the form as well? I think it would save you a great deal of pain, but get you almost the same benefit.
You could attach an ajax event to each input losing focus that would call the Controllers update method.
Most users would be surprised by this behavior though because it isn't the expected behavior of a web site.
If you use AJAX to call update, then here are a few things that might help: jQuery's serialize() function can help gather the form data into a post request without having to call the forms submit action. Using save(:validate => false) will bypass validation if you are saving drafts and want to skip validation until the final save.
I'm trying to develop an application which modifies a couple of tasks of the famous Online-TODO List RememberTheMilk (rememberthemilk.com) using the REST API.
Unfortunately the modifying takes a lot of time, so I want to give a feedback to the users.
My idea was just to display a couple of text lines (e.g. modifying task 1 of n...).
Therefore I used the periodically_call_remote on my page and called a which reads a Singleton.
In the request I store the text that should be displayed in the same singleton. But I found out, that once I set up a request, the periodically_call_remote does not update the specified div.
My question to this:
1. is this a good way to implement this behaviour?
2. if it is, how do get the periodically_call_remote to work during a submit?
Using a Singleton is most definitely a bad idea. In an advanced production setup it isn't guaranteed that subsequent requests will go to the same process or to the same machine (and subsequently will have a different Singleton). Plus, if you have many users, I don't even want to think about what'll happen to those poor Singletons.
Does any of this stuff actually need to go through your Rails app? It seems like you can call the RTM API via Javascript from the page the user is on and then update the page when the XHR request is complete.