Just a note before you read this, I'm not a programmer in RoR but I just wanted to validate that this is possible, so sorry in advance.
I have a quick question about using a secondary page. Here's how I want it to work:
I have a primary page that has some data that will be saved. I have a link to a secondary page that you save only to the buffer. This means that if I change it three times everytime i go back to look at it it shows the last value I changed it to.
At save time of the primary page, I want the information on the primary page and the secondary page to be validated and saved. If it fails, I don't want to save the information on either page. Is this possible in RoR? If so can someone explain to me how?
You could do this in a few ways:
Have one real page, but use JavaScript to hide and show parts of it as needed.
Store the object in the session, and only write it to the database at the end
Store the data in a temporary table and save it in the real table at the end
Related
I currently have a gsp page with pagination and bulk actions based off of checkboxes. I want to store the checked item ids as the user goes to the next page, but to do so I need to store the items the user has checked. I was wondering how I could store that in the GSP page?
Thank you.
I want to store the checked item ids as the user goes to the next
page, but to do so I need to store the items the user has checked. I
was wondering how I could store that in the GSP page?
You could store them in a GSP page simply by defining a variable in the page and assigning it a value of the ids, but that won't solve the problem you are trying to solve because that page will be gone by the time the user navigates to the next page.
Unless you are introducing some client side technology for managing state, a more common thing to do would be to submit the ids to the server and store them in a session or possibly in a database depending on the use case.
I have a object that i want to store for a moment. The object is in a controller for now, the controller will generate a view. A AJAX request is made from the view to next controller. For that moment i need the object previously stored. Previously, i used session and it worked well. But not sure it is the right thing to do. Is session the answer for this or is there anything else?
I have used cache also.but as per the cache concept.It will access for all the users.So one user data will be override to another.So the cached object data will be change for the same user.I need to handle the data storage for an particular user(Independent).
How is it possible? anyother approach is there please share me.
In Controller I have used Httpcontext.cache["key"]=dataset;
but some one suggested like this.but its not displaying
Explain:
In Controller: httpcontext.current.cache is not coming.
HttpContext.Currenthandler and HttpContext.Currentnotification properties only coming.So How can we handle the temp data storage in MVC.
Please help me.
You could use TempData if you want to store data for the next request only. If data should be accessible between multiple requests, then use Session. Here is short explanation of each one with examples.
As Alex said you could use TempData but if you want to use the data in multiple request, you could use TempData.Keep("YourKey") after reading the value to retain the data for the next request too. For your Information TempData internally uses Session to store your data (temporarily)
I would recommend URL parameters for a HTTP Get, or hidden form fields for a HTTP Post, if this is short lived. This is highly about avoiding the session.
But if it should really persist, then a database might be a reasonable location. Imagine a shopping cart that you don't want to dump just because a session timed out; because you'd like to remind the user next time about items they still haven't purchased.
Why not use the session? I don't generally recommend using the session, as you could find yourself with a global variable that two different browser windows are manipulating. Imagine a glass. One window is trying to fill it with Ice Tea. Another window is trying to fill it with Lemonade. But what do you have? Is it Lemonade? Is it Ice Tea? Or is it an Arnold-Palmer? If you try to put too much stuff on the session, and overly expect it to just be there, you might create an application that is non-deterministic if heaven forbid a user opens a second window or tab, and switches back and forth between the windows.
I'm more ok with Temp Data, if you truly have no other options. But this is not for persisting data for more than a second. Temp data will disappear after the first request reads it, as in, it's meant for a very temporary usage.
I personally only use TempData if I have to do a redirect where I can't otherwise keep it with me, or if I need to have that data for say generating a PDF or image that is going to be called via a HTTP Get by a viewer on the actual page, and then only if the model data is too large for the GET url ( many browsers only support just over 2000 characters, which long description or many fields could fill up.)
But again, pushing items around in hidden form variables, or in url parameters can be safe, because you have no multiple window use conflicts (each carries around its own data for peace of mind.)
I'm just starting to learn ASP.NET MVC and I'd like to know how I can retain model objects between subsequent requests to controller action methods?
For example say I'm creating a contact list web app. Users can create, update, rename, and delete contacts in their list. However, I also want users to be able to upload a contact list exported from other programs. Yet I don't want to just automatically add all the contacts in the uploaded file I want to give the user a secondary form where they can pick which uploaded contacts should be actualy added to their list.
So first I have a ContactController.Upload() method which shows an upload form. This submits to ContactController.Upload(HttpPostedFileBase file) which reads the file that was posted into a set of Contact model objects. Then I want to display a list of all the names of the contacts in the list and allow the user to select those that should be added to their contact list. This might be a long list that needs to be split up into multiple pages, and I might also want to allow the user to edit the details of the contacts before they are actually added to their contact list.
Where should I save the model objects between when a user uploads a file and when they finally submit the specific contacts they want? I'd rather not immediately load all the uploaded contacts into the back end database, as the user may end up only selecting a handful to actually add. Then the rest would need to be deleted. Also I would have to account for the case when a user uploads a file, but never actually completes the upload.
From what I understand an instance of a controller only lasts for one request. So should I create a static property on my Contact controller that contains all the latest uploaded contact model object collections? And then have some process that periodically checks the age of these collections and clears out any that are older then some specified expiration time?
A static property on the controller is trouble. First off, it won't work in a web farm and second it you'd have to deal with multiple requests from different users. If you really don't want to use your database you could use the ASP.NET Session.
No, you don't want a static property, as that would be static to all instances of the controller, even for other users.
Instead, you should create a table used to upload the data to. This table would be used as an intermediary between when the user uploads the data, and completes the process. Upon completion, you copy the contacts you want to keep into your permanent table, then delete the temporary data. You can then run a process every so often that purges incomplete data that is older than a specified time limit.
You could also use the HttpContext.Cache, which supports expiration (and sliding expiration) out-of-the box.
Alternatively, and perhaps even better (but more work) you could use cookies and have the user modify the data using javascript in her browser before finally posting it to you.
However, I'd strongly recommend to store the uploaded information in the database instead.
As you pointed out, it might be a lot of data and the user might want to edit it before clicking 'confirm'. What happens if the user's machine (or browser) crashes or she has to leave urgently?
Depending on the way you store the data the data in this scenario will probably be lost. Even if you used the user id as a cache key, a server restart, cache expiration or cache overflow would cause data loss.
The best solution is probably a combination of database and cookie storage where the DB keeps the information in a temporary collection. Every n minutes, or upon pagination, the modified data is sent to the server and updated in the DB.
The problem with storing the data in session or memory is what happens if the user uploads 50k contacts or more. You then have a very large data set in memory to deal with which depending on your platform may effect application performance.
If this is never going to be an issue and the size of the imported contacts list is manageable you can use either the session or cache to store the dataset for further modifications. Just remember to clear it when the user has committed the changes, you don't want a few heavy datasets hanging around in session.
If you store the dataset in session using your application controller then it will be available to all controllers while it is needed.
I have a form where the user can choose options from a lot of select boxes. The form is used to register several items from an RSS feed. The user fills in the form, clicks create and is presented with the same form for the next item in the list.
Sometimes, the same options are valid for several items in the list, and I would like to be able to save some of the selections done so the user doesn't have to make the same selection for the next items.
What is the best way of doing this? I've identified four ways of doing it:
Sessions
Just keep the values in the session hash. This will of course work and is very simple, but I have some undefined feeling that it is a bad idea. It will also not work if the user is using the form from different tabs in the browser.
Cookies
Basically the same as keeping them in the session, I think.
Profile
Can't be done in this case I believe, since profiles are shared between several users.
Database
The most complex way I've come up with is to keep the information in the database and use a query parameter to keep track of which information should be used. This is probably overkill, but in some ways the best way to me. I don't like the idea of keeping this kind of state in session or cookies.
Am I missing some way? Or something?
If after filling first form, some data is saved to db (object is created) then you can use this data from db to fill up new form.
If after filling first form, nothing is saved to db, then you can create in memory some objects based on params from previous post and based on this (on just on params) you can prepare new form. But of course data from previous form should be added as hidden fields in second form.
I'm making a simple CRUD app with ASP MVC and I want to have a confirm page when creating a new object and inserting it into the database.
The problem is that I'm having trouble passing the object between actions. I tried to save it in the session after it's created and then retrieving it when the user confirms, but I'm getting an InvalidOperationException when I try to insert it into the database ( I'm using Entity Framework )
I'm not even sure if I'm approaching this the right way. Any ideas?
What I like to do if the schema allows for it, is to have an active flag (and timestamp field) on the record. You insert on the first page without setting that flag. The confirm page merely sets the active flag. Another process can clean dead records that were not confirmed within a certain range of their timestamp. And the object or entity never ties up session memory.
edit for clarity: as a result you only pass the id of the created entity to the confirm page
Tim's is the best basic answer to this but if you don't want to include the extra logic you could also consider using hidden fields on the confirm page so confirming actually resubmits the form data (this means less DB trips and means that you don't have old unconfirmed entries sitting in the DB to filter out but means more data to and from the client).
Another alternative that might be preferred from a UI point of view is to have Tim's answer but if JavaScript is enabled make the submit button instead pop up a confirm screen, clicking OK would submit both the form and the confirmation in one go.