I have an Activerecord object called Foo:
Foo.attribute_names.each do |attribute|
puts Foo.find(:all)[0].method(attribute.to_sym).call
end
Here I'm calling all attributes on this model (ie, querying for each column value).
However, sometimes, I'll get an undefined method error.
How can ActiveRecord::Base#attribute_names return an attribute name that when converted into its own method call, raises an undefined method error?
Keep in mind this only happens on certain objects for only certain methods. I can't identify a pattern.
Thank you.
The NoMethodError should be telling you which method does not exist for what object. Is it possible that your find returns no record? In that case, [][0] is nil and you will get a NoMethodError for sure.
I would use .fetch(0) instead of [0], and you will get a KeyError if ever there is no element with index 0.
Note: no need for to_sym; all builtin methods accept name methods as strings or symbols (both in 1.8 and 1.9)
Maybe something to do with access? Like if a class has an attr_protected attribute, or something along that line. Or for attributes that are not database columns, which have no accessors defined?
Related
Why is NoMethodError not differentiated for nil in Ruby?
Calling a method on nil is an extremely common error and is usually caused by incorrect data being provided to the program. A NoMethodError on any other class usually implies an error in the code itself (e.g. why were you calling reconnect on a Document? There is likely an error in the code).
What problems are created if I add the following code to my project?
NilReferenceError = Class.new(NoMethodError)
class NilClass
def method_missing(symbol, *args)
raise NilReferenceError, "undefined method `#{symbol}' for nil:NilClass", caller
end
end
I want to do this because when I am triaging exceptions, a NilReferenceError is likely to be caused by bad data and the root cause is likely in another location (validation of input, for example). By contrast, a NoMethodError is likely to be a programming error rooted exactly at the line of the exception (easier to fix and also highly likely to happen 100% of the time).
What are the negative effects of adding code like that to my project?
I think this is just habits from other programming languages. In ruby, nil is a first class object, like an integer, a hash or your own class object.
After you see the "NoMethodError: undefined method xxx for nil:NilClass" error once or twice, you get used to it.
There is nothing wrong with monkeypatching nil to show a more descriptive error message, but it's not going to solve the root cause of the problem, which is coding practice that permits and propagates nil values.
Consider the following very contrived example:
def do_something(input)
object = fetch_something_with(input[element])
do_something_with(object)
end
A couple of ways this might blow up:
input hash does not contain element, and passes nil into fetch_something_with
fetch_something_with returns nil (by design or upon failure), which gets passed into do_something_with
An alternative approach might be:
def do_something(input)
object = fetch_something_with(validated_input)
object && return do_something_with(object)
end
def validated_input(input)
input.fetch(element) # fetch raises an exception if the value is not present
end
A bit more code, but it gives us peace of mind that this code isn't going to silently pass nil down the line to fail at some later point.
Of course, it doesn't make sense to be this paranoid in every single method, but it is good practice to have well thought out boundaries in your code, either at method or object level. Having nil slip by frequently is a sign that these borders need some strengthening.
Do you mean that, when doing something like b=nil; b.say_hello;, ruby will give you "undefined method `say_hello' for nil:NilClass (NoMethodError)" instead of something like (as in your claim) "undefined method `say_hello' for nil:NilClass (NilReferenceError)"?
Ruby is not wrong for this since nil is an object like other objects. It has methods like to_s, so ruby can't ban any call by just raising an exception saying "because it is nil, you cannot do anything. I will give you a NilReferenceError".
You can surely do as your code above if you know that what you are doing may prevent ruby's default behavior.
I write app which will give all my data from LinkedIn. I did all but I have this error line:
undefined method `find_all_by_full_profile_id' for #<Class:0x007f4779a08008>
what this means and how can I fix it?
Dynamic finders are no longer available in the most recent versions of ActiveRecord. Simply use
Model.where(full_profile_id: value)
where Model is the model name, and value is the value of the full_profile_id attribute.
I am using tire/elasticsearch for searching with mongoid, when I update the index of my documents I am getting the error undefined method 'as_document':
#document.tire.update_index
undefined method `as_document' for #<Array:0x10a40f870>
I have researched the mongoid method 'as_document' and found out that it only accepts single objects. When my document objects do not have comments, "#document.as_document" returns a single object and there is no error, however when the document has comments, "#document.as_document" seems to return an array and returns the error "undefined method `as_document' for #".
It seems that when #document has comments, it returns an array of hashes.
Is there any way that I can return the array (Array:0x10a40f870) so I can see where it is coming from?
How can I convert #document (which seems to be an array) back into a single object so that it can pass through as_document?
Why am I getting an 'undefined method as_document'
I have a Document model with a has_many relationship to comments
Rails: 3.2.12,
Mongoid: 3.1.4
1. Logger is your homie. I would recommend printing this wherever your logic exists so you can see exactly what array you are returning.
Something like this:
# your logic here
#your_array = ..set
logger.debug "MY ARRAY: #{#your_array}"
This will give you at least a good look at what you are dealing with if you can take a look at Webrick or whatever setup you have.
2+3. Mongoid stores Documents as an array of hashes so that is what you are probably looking at (but I haven't seen the exact code).
I dont believe there is anything wrong with your document definitions but I would take a better look at the [Relations Sections] of the Mongoid docs1
More specifically to question 2: take a look at the operations section.
I've tried to use ActiveSupport's (2.3-stable) try() on an instance of HttpParty::Response. I've got a pretty strange behavior:
> ro.parsed_response
{"error"=>"RecordInvalid", "description"=>"Record validation errors", "details"=>{"email"=> [{"description"=>"Email: foo#bar.com is already taken by another user"}]}}
> ro.try(:parsed_response)
NoMethodError Exception: undefined method `parsed_response' for #<Hash:0x11397d5d8>
In the first example, I send the parsed_response message to ro by using the dot notation. It works fine. In the second one, I try to call it using ActiveSupport's try(), and it (surprisingly) raises the NoMethodError exception.
Shouldn't try() have returned nil in this case? And why doesn't it find the "parsed_response" method, if I can call it using the dot notation, as seen in the first example?
Thanks in advance!
Have no idea how, but seems like ro object was "transfered" into a hash that has been sent a parsed_response method.
In Rails 2.3#ruby 1.8 undefined method for object raises an exception.
Besides, docs stay only for calling try on nil object and nothing about the object that doesn't have a specific method:
Unlike that method however, a NoMethodError exception will not be
raised and nil will be returned instead, if the receiving object is a
nil object or NilClass.
I have a Gem that deals with images that get modified. I want to modify it to update the old image but, I need to be able to get the object id.
Right now it uses the following code:
def respond_to?(method,*args, &block)
puts ("++++METHOD #{method.to_s} ARGS #{args} BLOCK #{block}")
args.each do |value|
puts ("ARGS #{value}")
end
but I don't know how to get id from something I pass in nor do I know how to pass the id in, I've tried
#asset.image.s_245_245(:asset_id=>#asset.id) with no success. Args returns nothing. What am I doing wrong?
Update: I am currently reading http://www.simonecarletti.com/blog/2009/09/inside-ruby-on-rails-extract_options-from-arrays/
Update: This too returned blank.
Your question is very unclear. How is the method respond_to? related to your problem with object id?
I am guessing that in reality you wanted to override method_missing, because now you do not call respond_to?, or it is not shown in your examples.
If you have not defined such method, calling image.s_245_245 will trigger method_missing (in the image object) with the parameters you used for respond_to?.
There is a rule, which says that if you use method_missing to handle some calls, then you should also modify respond_to?, and make it returning true when asked for the methods handled by method_missing.
As for object ID, there are two possibilities:
Every object in ruby responds to .object_id (which returns an internal identifier of every object)
ActiveRecord objects respond to .id (which is a primary key in the database).
This is just a side-note, because I suppose that if you start experimenting with method_missing instead of respond_to? you will know which one you want.