Is there a way to write a clean if nil then in a view. Assuming my lack of ruby is biting me here. Example,
If object nil, then return, nothing found
have
<%= #objects.count if #objects %>
want something like this
<%= #objects.count if #objects then "nothing found" %>
There are many ways to write something like this.
Something simple would be:
<% if #objects %>
<%= #objects.count %>
<% else %>
nothing found
<% end %>
If you get into a slightly more complex conditional I would suggest moving the logic into a helper and call it from the view. ex:
<%= count_for(#object) %>
Here's a good solution for you:
<%= "nothing found" unless #objects.try(:length).to_i > 0 %>
One of the issues is that you can't run count on a nil object. Therefore you need to use Rails' super handy .try() method to return nil when #objects = nil, rather than NoMethodError.
Next issue: You can't make a comparison between nil and a number using > so you need to convert the results of #objects.length to an integer which will return 0 for nil.
Lastly, try calling length rather than count. This will avoid running any extra queries when #objects is defined.
Avoids: SELECT COUNT(*) FROM 'objects'
Also if you want to display the count using this one-liner technique you can simply write up a shorthand if/else statement as follows:
<%= #objects.try(:length).to_i > 0 ? #objects.length : "nothing found" %>
One last option:
Use the pluralize method, which can handle a nil count:
Showing <%= pluralize( #objects.try(:length), 'object' ) %>
Sorry, I know this is pretty late, but hopefully helpful for someone else!
Related
I have an instance variable #tally_property, and if there are photos on that object I would like to cycle through the photos and show them.
So my code snippet looks like this:
<% if #tally_property.photos.present? %>
<% #tally_property.photos.each_with_index do |photo, index| %>
The issue is that based on the above, if #tally_property is nil, then the entire first line throws an error.
So is there a 'nil' check I can do that isn't bulky, i.e. I don't want to do if #tally_property.nil?, on both the primary object and the association, and is elegant and ruby & rails-esque?
I would use the safe navigation operator (&.) and write something like this:
<% #tally_property&.photos&.each_with_index do |photo, index| %>
...
<% end %>
In Ruby 2.3.0+ you can use the safe navigation operator:
#tally_property&.photos
ActiveSupport has a .try method that can be used to the same end in older versions of ruby:
#tally_property.try(:photos)
You can add a simple conditional to be able to safely iterate through the collection:
<% (#tally_property.try(:photos)||[]).each_with_index do |photo, index| %>
<% end %>
Rails 4 adds ActiveRecord::Relation#none and a change in behaviour so that associations always return a ActiveRecord::Relation. So its perfectly acceptable to write:
<% #tally_property.try(:photos).try(:each_with_index) do |photo, index| %>
<% end %>
After upgrading your app. Or you can use a partial and render:
<%= render partial: 'photos', collection: #tally_property.photos if #tally_property %>
Which removes the need for writing the iteration.
Use && (or and, they each have their sweetspot).
Taking it out of Erb for a moment, I would generally write something like this:
if #tally_property and #tally_property.photos.present?
Depending on photos I might use:
if #tally_property and #tally_property.photos
or perhaps:
if #tally_property and not #tally_property.photos.empty?
Sometimes I'll use a temporary variable:
if (photos = #tally_property && #tally_property.photos)
photos.each #…
That kind of thing.
I would recommend this episode of Ruby Tapas, And/Or for a longer (but still quick) look at it.
One more way, just select all photos connected to this tally_property:
example how it might be:
Photo.joins(:tally_property).each_with_index do |photo, index|
I'm getting this following error:
undefined method `assessment' for nil:NilClass
My code below has the conditional unless to exclude if the method is nil, but is not working. I have also tried the if conditional as well, but not no avail.
I think I need to default to a number if assessment is nil, but unsure on how to do that.
The date is formatted in milliseconds: 1482985235000
<% #sales.methods.each do |data| %>
<%= Time.at(data.assessment.assessment_date/1000).strftime("%d/%m/%Y") unless data.assessment.assessment_date.nil? %>
<% end %>
Try using safe navigation operator or have a chain of try.
data.try(:assessment).try(:assessment_date).nil?.
Or by using safe navigation operator.
data&.assessment&.assessment_date.nil?.
This error is generated when any method is called on nil. If data is nil then assessment will generate error if assessment is nil then assessment_date will. Either way you need to make sure both are present.
We generally don't use inline rescue and handle this type of scenarios by checking both objects. You can go with any of option or you can also check data.assessment.present? && data.assessment.assessment_date.present?
The error says that you are calling the method assessment on a nil... this means that the thing that is nil is data. Your conditional is checking whether data.assessment.assessment_date is nil... but it won't even get to the check for whether assessment_date is nil because it's already failing at data.assessment
I have found a solution to the problem. Not sure if it's the best method, but it works. I added rescue 0 to the end of the call.
<% #sales.methods.each do |data| %>
<%= Time.at(data.assessment.assessment_date/1000).strftime("%d/%m/%Y") rescue 0 %>
<% end %>
I had an impression that link_to_if should work with this code without any problem:
<%= link_to_if locker.student, locker.student.fullname, locker.student do %>
<div>more complicated</div>
<% end %>
I am getting a no method error on "fullname".
So, my impression was that when student exists, link will be created, otherwise block will be rendered.
However, it seems like name parameter is always executed, regardless the if condition, so it simply breaks when there is no student on locker.
Is this true?
If yes (weird), how can i do something like this? What i want is to avoid a standard if.else.
Thx
Yes its always executed: its an argument of the function.
You could do:
<%= link_to_if locker.student, locker.student.try(:fullname), locker.student do %>
<div>more complicated</div>
<% end %>
Or use a standard if wrapping the link_to
Elegant ways to avoid these problems are null objects and/or decorators
Can someone explain the logic behind this code?(This is the correct code btw)
<% if #request.query['first_name'] && !#request.query['first_name'].empty? %>
Welcome! <%= #request.query['first_name'] %>
<% else %>
Hi! What is your name?
<% end %>
My intuition is to write the following instead:
<% if #request.query.inspect['first_name'].empty? %>
Hi! What is your name?
<% else %>
Welcome! <%= #request.query.inspect['first_name'] %>
<% end %>
I am trying to have a user form where people can input their names, when there is no input yet the text above the form says "Hi! What is your name?" when there is an input it has a message saying "Welcome! *User_name*"
The first block of code is not intuitive to me, the second one would make more sense.. ANy advice on how to understand the code?
Your intuition is correct, though you need an alternative to empty?. Rails adds a few different methods you can use:
blank? returns true if the receiver is nil, an empty array, string, or hash, or a string with only whitespace.
present? returns true if blank? is false. So your condition could be:
<% if #request.query['first_name'].present? %>
Welcome...
(I find it's always more intuitive to start with the positive condition - it would work just as well to check blank?).
Edit: It's pretty likely you can skip the query method entirely if all you expect there is either a string or nil. Just use:
<% if #request.query['first_name'] %>
You need to check if it's nil before you can check if its empty, because you are checking a Hash#empty?
irb(main):001:0> nil.empty?
NoMethodError: undefined method `empty?' for nil:NilClass
from (irb):1
irb(main):002:0> {}.empty?
=> true
The code checks for hash key existence, then check if the value of the hash is present. This action can be done in one check using:
#request.query.try(:[], 'first_name').empty?
You can avoid the first condition inside the if statement by transforimng nil into an empty string. I don't know if that is what you meant to do but you almost had.
First, you shouldn't call inspect in the hash because it will transform the entire thing into a 'complex' string. What you want to do turn only the value inside the first_name option, because in that case if the name exists it will still be the same, and if it doesn't, it will be turned into "nil".
Secondly, the method inspect isn't the best choice here, because the returned string will never be empty, given that nil.inspect => "nil". What you should use is the method to_s, wich will behave like this when applied to nil: nil.to_s => "".
Finally, you could update your code to:
<% if #request.query['first_name'].to_s.empty? %>
Hi! What is your name?
<% else %>
Welcome! <%= #request.query['first_name'] %>
<% end %>
One of the most common reasons my web application fails is because a user sometimes lacks a certain attribute that a view expects it to have. For instance, most users in my application have an education (school, degree, etc.) entry in our system, but some users do not. Assuming my view looks something like this:
<% #educations.each do |education| %>
<%= education.school %>
<%= education.degree %>
<% end %>
I want to avoid "Pokemon" exception handling and feel that there has to be a better way around dealing with a "undefined method `degree' for nil:NilClass" error in the case that a user does not have an education entry in our database. This just seems like an ugly/tedious fix:
<% #educations.each do |education| %>
<% if education.school %>
<%= education.school %>
<% end %>
<% if education.degree %>
<%= education.degree %>
<% end %>
<% end %>
Any input is appreciated. Thank you!
As long as you know the first object you're working on won't be nil, the easiest way is to just do this:
- #educations.each do |education|
= education.try :school
= education.try :degree
The #try method is pretty handy. You can also call .to_s on anything you think might be nil, Ie:
- #educations.each do |education|
= education.school.to_s
= education.degree.to_s
This will convert nils to an empty string. This isn't as useful in the view IMO, but comes in handy a lot of times if you have input that is expecting to be a string and might be empty. Ie a method like:
def put_in_parenthesis(string)
"(" + string.to_s + ")"
end
You have a couple of options here.
The easiest to implement is the try method. It is used like so:
<%= education.try( :degree ) %>
The problem is that try() is viewed as a bit of an anti-pattern. As the reference indicates, you can achieve similar functionality with something like:
<%= education && education.degree %>
This isn't really a lot different, intellectually, in my opinion. A popular way of handling this a little more cleanly is the Null Object pattern, which is basically an object with defined neutral ("null") behavior.