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 %>
Related
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
I have created a very simple model called Discussion and one of the columns is a boolean called resolved. The idea being that once a discussion item has been resolved that value is set to true.
On the edit form, I tried to put in some logic based on the value of that field.
<%= form_for(#discussion) do |d| %>
...
<% if d.resolved == "true" %>
<p>The discussion is resolved</p>
<% else %>
<p>The discussion is not resolved</p>
<% end %>
<% end %>
However, I'm getting an error message
undefined method `resolved' for #<ActionView::Helpers::FormBuilder:0x00000101674678>
I tried adding an attr_accessor line to my model but that didn't do anything for me either. I'm not sure what I have to do to fix this. I'm pretty new to rails, so I'm sure that whatever the problem is it's probably pretty simple to fix, but I just don't get it. Thanks.
Because d represent an instance of the form builder, you want
<% if #discussion.resolved %>
If resolved is represented as a "boolean" in ActiveRecord.
every boolean column represents as predicate, so you can use:
if #discussion.resolved?
...
end
What you're looking for is the resolved? method.
<% if #discussion.resolved? %>
which is auto-generated for boolean columns.
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!
I would like to display a line of text only if an object called #foo is set.
In my view, I'm trying something like this:
<% if !#foo.new_record? || !#foo.nil? %>
Foo is not a new record or nil
<% end %>
But this fails, returning You have a nil object when you didn't expect it!
I'm pretty sure this happens because of the new_record? method.
How do I check if something is not a new record or nil without causing an error?
In PHP, it would be achieved by asking if(!empty($foo)) but even the empty? method in rails causes the same error to be returned.
Any ideas?
How about:
<% if !#foo.nil? && !#foo.new_record? %>
Hello!
<% end %>
First off, you need to be using AND logic rather than OR logic here, since any ActiveRecord object meets at least one the requirements of "not nil" or "not a new record".
Second, checking for nil first ensures that the second check isn't run if the first one fails. The error is thrown because you can't use #new_record? on an object that doesn't support it, so checking for nil first ensures that that method is never run on a nil.
Let me throw another answer just for fun.
unless #foo.nil? or #foo.new_record?
"Hello"
end
You might be interested in these as well:
<%= #foo.text if #foo.present? %>
or
<%= #foo.text unless #foo.blank? %>
I would check by if #foo && #foo.id. This checks that there is a #foo activerecord object and makes sure the id field is not empty. If the id field is empty, that means it's not a record in the database yet. I assume you are using id field in the table.
The simple way is
<% if !#foo.try(:new_record) %>
Hello!
<% end %>
Is there a reason why this object might be nil when it gets to the view? Sometimes adding conditional logic like this in the view can be a sign that something could be refactored and you are just masking a bigger problem.
I much prefer to use the andand gem for these checks.
if #foo.andand.id
"Hello!"
end
The call to .id will only be made on non-nil objects.