Unfortunately I'm probably still too much a Rails beginner, so, even though I thought about and tried different approaches, I didn't get to work what I want and now have to ask for help again.
I have a REST comment vote mechanism with thumbs up and down for each comment. That works fine, each handled with counter_cache to count. Now, based on these thumbs up and down votes, I want to calculate a plusminus value for each comment, thumbs_up-votes - thumbs_down-votes. Although I'm not sure if it's the most efficient way to deal with that, I am planning to have the plus-minus value as an extra integer attribute of the comment model (whereas the thumbs up and down are own models). So, what I basically want is, that when a thumbs_up is saved, the comment's plusminus attr automatically should be += 1, and respectively for the thumbs_down.save a -= 1.
How can I issue such an action from within the thumbs_up controller? Do I need to modify my form_for or is my approach completely wrong?
Is there an after_save callback to deal with an attribute of a different model?
From what you've given, it's hard to tell. But I'd say that if you need to show a comment's "thumbs up" and "thumbs down" independently, store them as fields for your Comment model. Then, just making a helper method in your Comment model to get a comment's rating:
def rating
thumbs_up - thumbs_down
end
Edit:
With your new comment, I'd still say make a helper method rather than a field.
#models/comment.rb
def rating
thumbs_up.all.length - thumbs_down.all.length #or whatever way you want to do this
end
if you don't want to mix two different models with helper methods that don't actually belong to neither of those models, you can use Observers http://api.rubyonrails.org/classes/ActiveRecord/Observer.html
your observer will watch one model and do something
Related
Book model has_many Ratings, which has overall attribute.
I want the Book's mean_rating attribute to be updated every time a rating is added/destroyed.
What is the easiest way to do it?
you can utilize the model lifecycle hooks, notable, after_create.
in your ratings model, you can write an after create hook that will update the mean_rating
#models/rating.rb
after_create :update_book_mean_rating
def update_book_mean_rating
new_mean_rating = self.book.ratings.sum(:overall) / self.book.ratings.count
self.book.update_attributes(mean_rating: new_mean_rating
end
you'll probably want to add validations / checks that makes sure a rating always has a book etc and doing something similar when destroying, but something like this should point you in the right direction
The easiest way (not thread-safe) is to use after_create/after_destroy callbacks in Rating model. See documentation on model callbacks
If you need thread safe solution you will need to update mean_rating in delayed job or something. This post might be a good start
I'm in the process of updating a website I made almost 2 years ago. It was my first real website and I made some mistakes (some more serious that others).
What apparently is one of my biggest is making database calls from the view.
I'm pretty damn sure there is a better way to do this:
Use Case:
Someone fills out a form for a new subject, populating the Subject table, and they have been marked "enrolled", Subject.enrolled = 1
Based on that, I now need to create a record in 5 other tables (such as Baseline)
Downhill from here, here is my method
Determine if the record exist based on subject_id from Subject (sub)
<$ if Baseline.where(subject_id: sub.subject_id).first != nil $>
If it does not exist, create the record, (otherwise display the link)
<%= Baseline.create(subject_id: sub.subject_id) %>
This all happens in the view, and creates a front-end table with links to each record in the process. So I'm creating records based on for-loop logic...
Question:
So I'm looking for direction. I don't want to guess how to do this - I'm pretty sure the model/controller should do this - I want to learn how to do it correctly. How do I create records automatically, based on a value in a table?
Thank you for your time.
Not quite sure how your domain and code looks like, but to answer this question: 'How do I create records automatically, based on a value in a table?', it seems that you could use ActiveRecord callbacks, like this:
class Subject < ActiveRecord::Base
after_commit :create_baseline_if_enrolled, on: [:create, :update]
private
def create_baseline_if_enrolled
return unless enrolled?
# enrolled? == true, you may create these models here
end
end
To answer your question:
It depends :) This is just one possible solution. Another one would be to put such a custom logic in your SubjectsController and call it directly from the #create, #update methods. Both approaches have pros and cons. For example, abusing callbacks (anywhere) makes code less readable and harder to debug. On the other hand, putting such logic in controllers puts a burden on you that you have to remember about calling it if you happen to be editing subjects in other places (but is more explicit). Whichever way you choose, remember not to make your classes too fat, for example try to use service object pattern to separate such custom logic as soon as you feel like it is getting out of hand. :) And don't forget about tests - when things go wrong, tests make refactoring easier.
I'm making an application that involves booking appointments for users. I have a User model and an AvailableDate model. The user has_many availble_dates and the AvailableDate belongs_to user.
I want to present a form for the user so that they can mark a couple of dates in a calendar and each of the dates they mark will become an AvailableDate object tied to that user.
At the moment my solution is to do all the work that a form_for helper would normally do manually. This involves a lot of javascript and is generally just getting far too messy.
I can't figure out how I should make a form_for tag work when I need to create potentially infinitely many dates. In theory a user could keep marking off dates in the future as available. If I knew how many dates I needed to create for a user, I could do user.available_dates.build, N times. But this doesn't work here.
Can anyone help? It like this problem should be pretty common. Am I designing my application wrong?
One technique is to render the fields for your association once, outside the form.
When the user performs whatever interaction that should create a new set of inputs you use javascript to clone the initial set of fields and insert them into the form. The one thing you need to do is change the name of these inputs so that they are unique. Usually people use the current time in milliseconds for this unique identifier.
Been there & have found several resources to help: Tutorial & Cocoon
The bottom line is you need to ensure child_index is unique for each field. The tutorial I use has child_index: Time.now.to_i to create a truly unique id, consequently allowing you to add as many fields as you want
The best way to do this:
Render fields_for as a partial (passing your form builder object)
When you want to add new field, create ajax_field action
Make ajax_field view have its own form_builder
Both your original & ajax_field forms will call the partial
On front-end, you can use JS to GET new form action & append field to page
I can give you code if you want
So basically I have a Book model that contains information like
book title (string)
author (string)
description (text)
etc.
Now on the front end I added the capability of dynamically adding more author fields. In the form I named it book[coauthor], so if I add a second author, I'd have a field book[coauthor][name_0].
What I'd like to achieve is combine book[author] and all book[coauthor][name_i] to one big string and separate each name with ,. (i.e. so with book[author] being "Alice" and book[coauthor][name_0] being "Bob" I should get "Alice,Bob" saved in book[author] in DB)
First Question: At this point is it better to do it with Javascript or with Rails (in controller)?
Second Questiion: Currently I'm doing it in the Rails controller but got Can't mass-assign protected attribute 'coauthor'. However I don't want to make it a real attribute since all I need is some processing before saving all the information to the author field. What should I do?
Thanks guys.
The first question is a bit loaded, and you might get some heated disagreements but the way I look at it is this. Not everybody runs with Javascript enabled, so I make sure I have a way to do everything through Rails myself.
In this case, it's actually quite easy.
The first thing I recommend is to not send the coauthors as part of the params[:book]. Instead, send them separately as a params[:coauthors]. Then in your controller you can do this:
#book = Book.new(params[:book])
#book.author = ([#book.author] + [params[:coauthors]]).join(",")
#book.save
Actually, it may be better to update params[:book][:author] since that would work for both create and update. Either way, I hope that helps.
To the first question: I don't see any compelling reason to one over the other. JavaScript might provide a bit more ability to validate/fix formatting in this field in 'real time', but I'm not sure that's particularly important.
To the second question: You don't need to make something a real attribute in order to make it accessible. You've presumably created coauthor as a virtual attribute using attr_accessor, but this doesn't automatically add it to the mass-assignment whitelist. To do that, also add it to your attr_accessible list.
I've come across an oddity in ActiveRecord's #relationship_ids method (that's added automatically when you declare 'has_many'), which saves immediately for existing records, which is causing me some issues, and I wonder if anyone had any useful advice.
I'm running Rails 2.3.5.
Consider this simple scenario, where an article has_many tags, say:
a = Article.first
a.name = "New Name" # No save yet
a.author_id = 1 # No save yet
a.tag_ids = [1,2,3] # These changes are saved to the database
# immediately, even if I don't subsequently
# call 'a.save'
This seems surprising to me. It's specifically causing problems whilst trying to build a preview facility - I want to update a bunch of attributes and then preview the article without saving it - but in this instance the tag changes do get saved, even though no other fields do.
(Of possible relevance is that if 'a' is a new article, rather than an existing one, things behave as I'd expect - nothing is saved until I call 'a.save')
I have a fairly nasty workaround - I can override the tag_ids= method in my model to instead populate an instance variable, and actually save the related models in a before_save callback.
But I'd love to know of a simpler way than me having to do this for every model with a has_many relationship I'd like to create a preview facility for.
Does anyone have any fixes/workarounds/general advice? Thanks!
There's a reason things are this way. It's called foreign keys. In a has many relationship, the information that links to the model that has many is stored outside of that model as a foreign key.
As in Articles, has many tags. The information that links a tag to an article is stored either in the tags table or in a join table. When you call save on an article you're only saving the article.
Active record modifies those other records immediately. Except in the case where you're working with a new article that hasn't been saved yet. Rails will delay creating/updating the associated records if it doesn't know which id to place in the foreign key.
However, if you're modifying existing records, the solution you've decided on is really all that you can do. There's an even uglier hack using accepts_nested_attributes_for, but it's really not worth the effort.
If you're looking to add this behaviour to many models but not all models, you might want to consider writing a simple plugin to redefine the assigment the method you need and add the call back in a single class method call. Have a look at the source of something like acts_as_audited to see how it's done.
If you're looking to add this behaviour to all models, you can probably write a wrapper for has_many to do that.