I have this Ruby code in a script:
$dev_input=gets.chomp.downcase!
if $dev_input.include? "/"
check_developer_commands()
else
puts ">>Invalid Command<<"
continuing_dev_mode()
end
The problem is, whenever I try and run the script containing this, I get an error spat back at me that says :
dev_continue_main.rb:3:in 'continuing_dev_mode': undefined method 'include?' for nil:NilClass (NoMethodError)
Any idea what this error might be? I'm pretty sure that this is the proper way to use the .include? method. I've done some research, looked at tutorialspoint.com and some other sites, but they agree that this is the proper way to use this method.
I checked the error message and it confirmed that the third line in this script/my example is the source of the problem, so it's not some other instance of this method throwing an error.
Any thoughts? Please Help!
The problem is that $dev_input is nil. That stems from applying downcase! in defining $dev_input. I don't know why you want to possibly assign nil to $dev_input, and at the same time claim that calling include? on it is the right way. I don't get your intention for doing that, but if you instead had $dev_input = gets.chomp.downcase, then it wouldn't cause such error.
Related
Probably a stupid question but I was following along this article and came across a bit of code I couldn't quite grasp. Here it is:
class CreateArticle
attr_reader :validate_article, :persist_article
def initialize(validate_article, persist_article)
#validate_article = validate_article
#persist_article = persist_article
end
def call(params)
result = validate_article.call(params)
if result.success?
persist_article.call(params)
end
end
end
More specifically, the problematic line is this:
if result.success?
Here's my problem with it: where did the success? method come from? It's not default in Ruby, and result is a local variable, so it should be nearby. But even if it's just omitted in the code sample, where would it have to be defined for that line to work? Everywhere I tried to define it just gave me an 'undefined method' error.
For example, I tried to define it both in the CreateArticle class and in the (only alluded to) ValidateArticle class, the obvious culprits, but no dice.
Update:
The reason I ask is not so much about what success? does as it is because I'm interested in using the pattern in my code. So, for example, my version of the success? method could be just checking whether a value got updated, or an item was inserted into an array. For example, let's say it's just this:
def success? # or self.success?
return true
end
Problem is, I can find no place where I can put this that works. I even created a module just for it and included it into the class, and still it doesn't work (it just returns 'undefined method'). So I'm still at a loss as to where I would have to define such a method so that it would work the way it looks like it should.
It's a method that comes with rails. It checks.for a server response with a 200 code. If it gets a 200 code it returns true else it returns false. Read the rails API docs about it... https://apidock.com/rails/v3.2.3/ActiveResource/Response/success%3F
Actually . success? is a built in ruby method. Check here. What it actually does is checking Stat and returns a boolean.
I did some more digging around the blog and from what I found I suspect that the code is probably making use of the dry-monads gem:
You can explicitly check the type by calling failure? or success? on a monadic value.
It's not explicit in the code excerpt but it's the only thing that makes sense.
I am trying to make a post request in Ruby and I am getting inconsistent behaviour. I am currently using ruby-2.0.0-p598 on OSX.
When using PRY and I type the following post command:
HTTParty.post(#base_uri + '/method/?argument1&api_key=' + #api_key)
I get a successful respond from the API. However when I run it through my specs or inside the class I get:
undefined method `+' for nil:NilClass
I know it has to do with the plus sign, but I find it weird that I am getting a different behaviour. Can you please suggest what is the correct way of doing this?
Thanks in advance.
Good day
Behavior correct - some variable = nil.
You have check variables, or (in this case it is better not to do) call to_s:
HTTParty.post(#base_uri.to_s + '/method/?argument1&api_key=' + #api_key.to_s)
It looks like #base_uri and/or #api_key is null. Please double check if they are initialized with valid strings or not. Then try
HTTParty.post("#{#base_uri}/method/?argument1&api_key=#{#api_key}")
In this case, ruby will automatically try to convert #base_uri and #api_key to string so no need to call to_s method explicitly.
I am a junior rails developer and was advised to use Class.find(id) to query the database instead of Class.find_by_id(id) which I previously had. The reason I was told is because the former would raise an exception while the latter would return nil. I realize this happens but I am wondering what the high level conceptual logic is for doing it this way. Why do I want the exception? Is this a rails standard where I would always prefer a method that returns an exception as opposed to nil?
You typically want the exception because you're typically doing Foo.find(id) based on data input coming from the user, such as clicking on a link.
For example, you show the user a list of items. There are links like this:
http://example.com/items/100
http://example.com/items/101
http://example.com/items/102
The user clicks the first link, and expects to see item 100.
Your code does this:
Item.find(100)
You expect to find the item, because app created the item link. You'd be surprised if the item didn't exist.
(Corner case surprises are possible: perhaps the item was deleted, or perhaps a hacker is sending in missing ids, etc. Using exceptions helps you handle this as an exceptional circumstance.)
Exceptions are preferred to nil for this, because you want the code to fail immediately so you don't accidentally send the nil on to some other method.
Ruby nil objects can be confusing because they evaluate to falsey and also because nil.id == 4 because of how Ruby uses C. Error messages show up like "Warning: Object#id will be deprecated" or "undefined method for 4:Fixnum".
Nils are problematic as a return type in Ruby in general. There's a great (paid) screencast by Gary Bernhardt that explains why you want to avoid returning nil from methods, but in a nutshell: when a method returns nil, and that nil gets passed up through a chain of method calls and something goes wrong somewhere, it can be extremely difficult to figure out where the actual problem occurred.
Say, for example, you have something like this:
foo_model = MyModel.find_by_name('foo')
# some more lines of code
do_something(foo_model)
and a method:
def do_something(model)
# some stuff stuff
some_other_method(model)
end
Now, if MyModel.find_by_name('foo') returns nil, that nil will be carried along without any errors until it actually has to do something. Say, in some_other_method, you actually try to call something on model, say model.save, you will get an error:
undefined method 'save' for nil:NilClass (NoMethodError)
The trace will carry you back up the method calls, but it will not mention the line that was actually problematic, where you assign MyModel.find_by_name('foo') (which evaluates to nil) to foo_model.
You can imagine that in a real application, the code can be much more complex, and returning nil can make it much more difficult to figure out the source of an error.
An exception, in contrast, tells you immediately where the problem is, and the trace will go back to the line where it occurred. That's one reason (there are others, I imagine) why in general, returning nil is not a good idea.
Hope that helps.
I am using Ruby to work with the Rally API. I am trying to reference the testcase method. The method being Manual or Automated, but I always get an error. I am using Ruby, so I don’t know if method is a reserved word in Ruby, or what is happening. Could you please let me know how to reference the test case method?
I am able to do:
testcase.objective
testcase.priority
etc.
But I can’t do
testcase.method
I always get this error.
‘method’: wrong number of arguments (0 for 1) (ArgumentError)
Are you using rally_rest_api or rally_api?
If you are using rally_rest_api - Charles is correct. try testcase.elements[:method]
(fieldname downcased and underscored as a symbol)
If you are using rally_api - http://rubygems.org/gems/rally_api -
Getting fields can just be:
testcase["FieldName"]
Hope that helps.
You just need to capitalize the names when trying to access built-in fields (i.e. fields that are not custom). I came across this problem myself and using tc.Method instead of tc.method fixed it.
The reason this error shows up can be seen in the docs for Object#method which, as you've likely figured out by now, causes your code to call the method method instead of access the field named method.
I'm trying to do this tutorial-> http://netbeans.org/kb/docs/ruby/rapid-ruby-weblog.html
BUT
its giving me this error:
NameError in PostsController#index
uninitialized constant PostsController::Posts
I don't know whats wrong
Somewhere in the files processed for your action you have tried to use a class called Posts. Try using Post instead of Posts. There is no Posts class. You are probably looking for the Post model class.
Look for the mistake in either in the index method of posts_controller.rb or in app/views/posts/index.html.erb. The error message should help you find the offending line.