Rails ERB iterate over array - ruby-on-rails

I'm trying to experiment with blocks and how to iterate over collections in ERB. I have a models in a one-to-many relatinship (Channel and their corresponding types).
controller
class HomePageController < ActionController
def index
#channels = Channel.all
end
end
Then in the view, I iterate over all the attributes belonging to a Channel. When I want to print all types, this code gives me the desired output:
view
<% #channels.each do |channel| %>
<% #types.each do |type| %>
<%= Type.find(type).name %>
<% end %>
<% end %>
At first I tried to achieve this by using the yield keyword in a neat one-liner but I couldn't manage to print anything to the browser, only to the console
<% #types.each {|type| yield Type.find(type).name } %>
Is there an equivalent one-liner?

First of all this method is so inefficient, you are doing n-queries, to find each record of type Type instead convert those into an array of types by using a single query in the controller, assume that that array is in type_ids
# controller
#channels = Channel.includes(:types) # avoiding n+1 queries
# view
<% #channels.each do |channel| %>
# some channel info output
<% channel.types.each do |type| %>
<%= type.name %>
<% end %> # types loop
<% end %> # channel loop
As #Almaron mentioned, you could render a partial for more simplification, if you have a partial called _type.html.erb you can call render directly
# view
<%= render channel.types %>
Rails will do all the iterating and rendering.

First of all, this kind of code does not belong to the view. Don't tackle the database from the view (in your case Type.find()). Move it to the controller where it belongs.
The second thing to note is the difference between <%= and <% tags. The first one outputs the returned result, while the second one doesn't. The problem with .each is that it returns the object it has been used on, so in your case if you just go <%= #types.each {|type| Type.find(type).name } %> you'll get the #types array printed out.
If you want to simplify that code, you can use a helper method for iterating and a partial for rendering each item. That way you get something like this
<% collection_iterate #items, 'item_partial' %>

Related

Ruby on Rails: Store array value in variable and use as string

I'm in the process of refactoring some code. I'm trying to use arrays in my view as part of a for loop that makes columns in a table.
I have defined the arrays in my controller:
subjects_controller.rb
def index
...
#CRFS_TO_VIEW = [Baseline, TreatmentCompletion]
#CRF_PATH = {Baseline => 'baseline_path', TreatmentCompletion => tc_path}
end
So my goal; as the function iterates over #CRFS_TO_VIEW, the correct path is selected from #CRF_PATH and appended to the link_to function.
indext.html.erb
<% #CRFS_TO_VIEW.each do |crf| %>
<% path = #CRF_PATH[crf] %>
<%= link_to "edit", path(crf.where(subject_id: sub.subject_id).first %>
<% end %>
I also tried :
<%= link_to "edit", #CRF_PATH[crf](crf.where(subject_id: sub.subject_id).first %>
Which didn't work. I feel I must be getting close, any help or insight would be greatly appreciated.
Thanks.
A few things:
a. You should save yourself some time and loop through the dictionary instead of the array:
<% #CRF_PATH.each do |crf, path| %>
...
<% end %>
b. You are getting a string from the loop - you can invoke the equivalent method with send:
<%= send(path, ...) %>
c. You can simplify your retrieval of the objects using:
crf.find_by(subject_id: sub.subject_id)
That said - this seems like a pretty bad way of doing things. I'd recommend instead adding a view helper:
def crf_path(crf)
case crf
when Baseline then baseline_path(crf)
...
end
With something like this you could use (notice changed the find_by to find_by! for safety as well):
<% #CRFS_TO_VIEW.each do |crf| %>
<%= link_to "edit", crf_path(crf.find_by!(subject_id: sub.subject_id) %>
<% end %>
Finally instance variables should NOT be named upper case. If you want to use a constant define it as a constant (otherwise use lower case names).

How to show items which belong to the category

I'd like to answer what I'm doing wrong. So, I'm trying to list all products that belong to the category, on the category's page. Here is the code:
<% #product = Product.all%>
<% #product.where("category_id = ?", params[:#category_id]).each do |product| %>
<%= product.title %>
<%end%>
But there is nothing showing up on my page. So, what's wrong?
There is a whole bunch of problems with your code.
1) Read guides for starters.
2) You have to define an instance variable in controller's action, and then in view just use this variable in your loop. I assume, it is index action you have view for. If so,
def index
# this variable will be used in view
#products = Product.where(category_id: params[:id])
end
and then in view
#products.where(category_id: params[:category_id]).each..
Also, Make sure you have in params what you expect (inspect the params if not sure).
3) You do not execute code, so nothing is being output.
In erb to make things being evaluated you either use - or =. You used none of these. Here is how it should look like:
# notice dash at the beginning of the line
<%- #products.each do |product| %>
<%= product.category_id %>
<% end %>
probably you want read :category_id from params, not :#category_id (so it should be params[:category_id], not params[:#category_id]).

Correct way of rails caching complex query

I am new to caching and I'm not sure what my best course of action is.
I want to cache a part of my view that relies on a complex query. The query looks something like:
#sessions_next_week = group_by_wday(LittleClassSession.location_only([1,2]).age_range_only(age_from, age_to).supports_dropins_only(support).approved_users_only.next_week)
Above you'll see a number of scopes and methods called. The view renders an instance variable named #sessions_next_week like so:
<% #sessions_next_week.each do |wday, lcs| %>
<h3><%= wday %></h3>
<%= render partial: 'table_head' %>
<% lcs.each do |s| %>
<%= render partial: 'table_row', :locals => {:s => s, :show_day => true} %>
<% end %>
<%= render partial: 'table_foot' %>
<% end %>
As you can see, #sessions_next_week is iterated through, and its children are iterated through. Given this, and given the nature of the query results in the instance variable, I'm not sure where to implement the caching. In the model? In the view?
So my questions are:
Do I need model caching or can I do this in the view?
What's the correct implementation?
The solution is to simply add two character:
#sessions_next_week ||= group_by_wday(LittleClassSession.location_only([1,2]).age_range_only(age_from, age_to).supports_dropins_only(support).approved_users_only.next_week)
This is called memoization, and you can look it up. Here's one source: http://www.justinweiss.com/articles/4-simple-memoization-patterns-in-ruby-and-one-gem/

How to return ActiveRecord Association Proxy on ERB

so I have a standard has_many through association in my models, very similar to the question here: Loop through ActiveRecord::Associations::CollectionProxy with each
I used the advice in that problem but I think I am having some trouble getting it through on my ERB file so that it shows up in my app. At the moment I have the following:
<%= #memberships.map do |a| %>
<%=a.name%>
<% end %>
In this scenario, the membership model is the one through which users and organizations have many though (#memberships = #user.organizations). So the #memberships.class returns
ActiveRecord::Associations::CollectionProxy::ActiveRecord_Associations_CollectionProxy_Organization
on the rails console. So the moment, in the browser the code returns on a page where the user is in two orgs:
orgone orgtwo["\n", "\n"]
I just don't know how to manipulate the proxy classes to return what I want. Thanks!
UPDATE:
I figured it out, I had to remove the = at the top of the block, and I added some styling with a comma:
<% #memberships.map do |a| %>
<h3><%=a.name %> <%= ", " unless a == #memberships.last %></h3>
<% end %>
If you want to print the name of each membership, what you want is
<% #memberships.each do |membership| %>
<%= membership.name %>
<% end -%>
The <% prefix in ERB executes code without appending the results to the output buffer, while the <%= prefix outputs the string representation of the result of the expression. Since each returns an enumerator, a <%= will return the string representation of the enumerator which is something like #<Enumerator:0xDEADBEEF.

how to call a method in a controller from the view and then iterate the values returned from the method in the same view

I have a scenario where i am calling a Controller method from the view,that returns an array of pages,which can be either nil or must be having values.i need to iterate that array in a for loop to generate a dynamic list in my view.pls help
Implementing logic in your controllers is generally not a good idea you should move logic into the corresponding model.
But if you really want to you can use controller variable to reach the actual controller from your view.
Example:
<p>
Now we're printing out the result of the some_method:
<%= controller.some_method.inspect %>
</p>
Iterating through the returned value is easy:
<ul>
<% controller.some_method.each do |item| -%>
<li>item.inspect</li>
<% end -%>
</ul>
Probably the visibility of the method in your controller is not public, so you may need to use the Object#send method.
<%= controller.send(:my_protected_method).inspect %>
Update
To handle the nil reponse, I would create a helper method in the ApplicationHelper class:
def my_method
(controller.my_method || [])
end
And then in the view:
<% my_method.each do |item| -%>
<%= item.inspect %>
<% end %->

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