I have an object and want to access to some data but I have an error.
This is the object:
list = [{"id"=>0,"title"=>"Purple Rain"}, {"id"=>1,"title"=>"Life is a flower"},]
With binding.pry, i tried to access to the title of the first object by:
list.first.title
Can you tell me why it doesn't work? If i do "list.first", it will show the first object without any problem but when i want to access to only one data, i got this error:
NoMethodError: undefined method `title' for #<Hash:0x...
Thanks for your help
Hash doesn't have dot syntax. OpenStructs do. If you want to use dot syntax, then you can convert to openstruct if you want. But using what Sebastian suggested is fine.
list
# => [{"id"=>0, "title"=>"Purple Rain"}, {"id"=>1, "title"=>"Life is a flower"}]
list.first["title"]
# => "Purple Rain"
require 'ostruct'
# => true
obj = OpenStruct.new(list.first)
# => #<OpenStruct id=0, title="Purple Rain">
obj.title
# => "Purple Rain"
I would like to get any additional GET and POST params in Rails without Rails' own additions such as controller, format, etc...
params.inspect gave me what I want but it has some keys that Rails adds for me such as controller or format. I only want to get user input GET and POST params as hash. How can I do that? I cannot find anything.
URL:
http:/test.com/some/path?query1=1&query2=1
Run:
puts params.inspect
Expected:
{"query1"=>"1", "query2"=>"1"}
Actual:
{"query1"=>"1", "query2"=>"1", "format"=>":json", "controller"=>"get", "action"=>"index", "folder"=>"some/path"}
Also this can be combined with POST request. I only want to filter them and only get them as hash.
I execute this from inside of a controller. Rails 5 used.
You should have permitted params (Strong parameters).
In your controller have permitted params method.
def your_params
params.permit(:query1, :query2)
end
If you wish to have a hash of those you can do
your_params.to_h #This will return hash of permitted params
Update:
Incase you have multiple query* type of parameters you can select them and permit!. Here is a command line explanation
# passing the list of parameters
> params = ActionController::Parameters.new({query1: 'aa', query2: 'bb', query3: 'cc', controller: 'users', action: 'index'})
=> <ActionController::Parameters {"query1"=>"aa", "query2"=>"bb", "query3"=>"cc", "controller"=>"users", "action"=>"index"} permitted: false>
# Select all the parameters of type query<integer>
> all_queries = params.select {|i| i.match?(/query\d/) }
=> <ActionController::Parameters {"query1"=>"aa", "query2"=>"bb", "query3"=>"cc"} permitted: false>
# mark the selected as permitted
> all_queries.permit!
=> <ActionController::Parameters {"query1"=>"aa", "query2"=>"bb", "query3"=>"cc"} permitted: true>
# get them as hash
> all_queries.to_h
=> {"query1"=>"aa", "query2"=>"bb", "query3"=>"cc"}
Controller method will look like
# getting all query<integer> like params
def your_params
params.select {|param| param.match?(/query\d/}.permit!
end
In the controller, you have access to a request object. request has a method query_parameters, which will return a hash of just the explicitly supplied parameters.
`request.query_parameters`
http://api.rubyonrails.org/classes/ActionDispatch/Request.html#method-i-query_parameters
I have the following method in one of my Ruby on Rails apps controllers:
decoded_translations = params[:translations].collect do |encoded_source, encoded_translation|
decoded_source = URI.decode(encoded_source).gsub("\r\n", "\n")
decoded_translation = URI.decode(encoded_translation).gsub("\r\n", "\n")
[decoded_source, decoded_translation]
end
When I run my tests this returns me:
undefined method `collect' for #<ActionController::Parameters:0x007ff0e810c6e8>
How can I fix this?
Before using collect method on array/hash comming in the paramters, you have permit the required param and convert it to array/hash. Then only we can able to apply collect method on it.
Ex:
permit_params = params.permit(refresh: [:key, :scope, types: []])
permit_params[:refresh].methods.grep /collect/
# => []
permit_params[:refresh].to_h.methods.grep /collect/
# => [:collect, :collect_concat]
params[:refresh].to_h
# => ActionController::UnfilteredParameters: unable to convert unpermitted parameters to hash
# from /Users/mohanrajr/.rbenv/versions/2.2.2/gemsets/<app>/gems/actionpack-5.1.2/lib/action_controller/metal/strong_parameters.rb:258:in `to_h'
I have the following params that are being submitted:
{"utf8"=>"✓",
"course"=>
{
"title"=>"Test", "roles"=>["Tuesday", "Thursday"]
}
}
My question is: How do I iterate through the "roles" params to "add_role"?
I am currently trying this iteration, but it is not working:
#course.user_id = current_user.id
params['course']['roles'].each do |key, value|
#course.add_role(key['course']['roles'])
end
I get the following error: undefined method '[]' for nil:NilClass
What am I doing wrong with iterarting the params?
Thank you!
params['course']['roles'] is the array ["Tuesday", "Thursday"], not a hash.
In your loop, key takes the value of a role string, "Tuesday"['course'] returns nil and nil['roles'] causes your error.
You seem to be trying to do this:
params['course']['roles'].each do |role|
#course.add_role(role)
end
This question already has answers here:
How to avoid NoMethodError for nil elements when accessing nested hashes? [duplicate]
(4 answers)
Closed 7 years ago.
In Rails we can do the following in case a value doesn't exist to avoid an error:
#myvar = #comment.try(:body)
What is the equivalent when I'm digging deep into a hash and don't want to get an error?
#myvar = session[:comments][#comment.id]["temp_value"]
# [:comments] may or may not exist here
In the above case, session[:comments]try[#comment.id] doesn't work. What would?
You forgot to put a . before the try:
#myvar = session[:comments].try(:[], #comment.id)
since [] is the name of the method when you do [#comment.id].
The announcement of Ruby 2.3.0-preview1 includes an introduction of Safe navigation operator.
A safe navigation operator, which already exists in C#, Groovy, and
Swift, is introduced to ease nil handling as obj&.foo. Array#dig and
Hash#dig are also added.
This means as of 2.3 below code
account.try(:owner).try(:address)
can be rewritten to
account&.owner&.address
However, one should be careful that & is not a drop in replacement of #try. Take a look at this example:
> params = nil
nil
> params&.country
nil
> params = OpenStruct.new(country: "Australia")
#<OpenStruct country="Australia">
> params&.country
"Australia"
> params&.country&.name
NoMethodError: undefined method `name' for "Australia":String
from (pry):38:in `<main>'
> params.try(:country).try(:name)
nil
It is also including a similar sort of way: Array#dig and Hash#dig. So now this
city = params.fetch(:[], :country).try(:[], :state).try(:[], :city)
can be rewritten to
city = params.dig(:country, :state, :city)
Again, #dig is not replicating #try's behaviour. So be careful with returning values. If params[:country] returns, for example, an Integer, TypeError: Integer does not have #dig method will be raised.
The most beautiful solution is an old answer by Mladen Jablanović, as it lets you to dig in the hash deeper than you could with using direct .try() calls, if you want the code still look nice:
class Hash
def get_deep(*fields)
fields.inject(self) {|acc,e| acc[e] if acc}
end
end
You should be careful with various objects (especially params), because Strings and Arrays also respond to :[], but the returned value may not be what you want, and Array raises exception for Strings or Symbols used as indexes.
That is the reason why in the suggested form of this method (below) the (usually ugly) test for .is_a?(Hash) is used instead of (usually better) .respond_to?(:[]):
class Hash
def get_deep(*fields)
fields.inject(self) {|acc,e| acc[e] if acc.is_a?(Hash)}
end
end
a_hash = {:one => {:two => {:three => "asd"}, :arr => [1,2,3]}}
puts a_hash.get_deep(:one, :two ).inspect # => {:three=>"asd"}
puts a_hash.get_deep(:one, :two, :three ).inspect # => "asd"
puts a_hash.get_deep(:one, :two, :three, :four).inspect # => nil
puts a_hash.get_deep(:one, :arr ).inspect # => [1,2,3]
puts a_hash.get_deep(:one, :arr, :too_deep ).inspect # => nil
The last example would raise an exception: "Symbol as array index (TypeError)" if it was not guarded by this ugly "is_a?(Hash)".
The proper use of try with a hash is #sesion.try(:[], :comments).
#session.try(:[], :comments).try(:[], commend.id).try(:[], 'temp_value')
Update: As of Ruby 2.3 use #dig
Most objects that respond to [] expect an Integer argument, with Hash being an exception that will accept any object (such as strings or symbols).
The following is a slightly more robust version of Arsen7's answer that supports nested Array, Hash, as well as any other objects that expect an Integer passed to [].
It's not fool proof, as someone may have created an object that implements [] and does not accept an Integer argument. However, this solution works great in the common case e.g. pulling nested values from JSON (which has both Hash and Array):
class Hash
def get_deep(*fields)
fields.inject(self) { |acc, e| acc[e] if acc.is_a?(Hash) || (e.is_a?(Integer) && acc.respond_to?(:[])) }
end
end
It can be used the same as Arsen7's solution but also supports arrays e.g.
json = { 'users' => [ { 'name' => { 'first_name' => 'Frank'} }, { 'name' => { 'first_name' => 'Bob' } } ] }
json.get_deep 'users', 1, 'name', 'first_name' # Pulls out 'Bob'
say you want to find params[:user][:email] but it's not sure whether user is there in params or not. Then-
you can try:
params[:user].try(:[], :email)
It will return either nil(if user is not there or email is not there in user) or otherwise the value of email in user.
As of Ruby 2.3 this gets a little easier. Instead of having to nest try statements or define your own method you can now use Hash#dig (documentation).
h = { foo: {bar: {baz: 1}}}
h.dig(:foo, :bar, :baz) #=> 1
h.dig(:foo, :zot) #=> nil
Or in the example above:
session.dig(:comments, #comment.id, "temp_value")
This has the added benefit of being more like try than some of the examples above. If any of the arguments lead to the hash returning nil then it will respond nil.
#myvar = session.fetch(:comments, {}).fetch(#comment.id, {})["temp_value"]
From Ruby 2.0, you can do:
#myvar = session[:comments].to_h[#comment.id].to_h["temp_value"]
From Ruby 2.3, you can do:
#myvar = session.dig(:comments, #comment.id, "temp_value")
Another approach:
#myvar = session[:comments][#comment.id]["temp_value"] rescue nil
This might also be consider a bit dangerous because it can hide too much, personally I like it.
If you want more control, you may consider something like:
def handle # just an example name, use what speaks to you
raise $! unless $!.kind_of? NoMethodError # Do whatever checks or
# reporting you want
end
# then you may use
#myvar = session[:comments][#comment.id]["temp_value"] rescue handle
When you do this:
myhash[:one][:two][:three]
You're just chaining a bunch of calls to a "[]" method, an the error occurs if myhash[:one] returns nil, because nil doesn't have a [] method. So, one simple and rather hacky way is to add a [] method to Niclass, which returns nil: i would set this up in a rails app as follows:
Add the method:
#in lib/ruby_extensions.rb
class NilClass
def [](*args)
nil
end
end
Require the file:
#in config/initializers/app_environment.rb
require 'ruby_extensions'
Now you can call nested hashes without fear: i'm demonstrating in the console here:
>> hash = {:foo => "bar"}
=> {:foo=>"bar"}
>> hash[:foo]
=> "bar"
>> hash[:doo]
=> nil
>> hash[:doo][:too]
=> nil
Andrew's answer didn't work for me when I tried this again recently. Maybe something has changed?
#myvar = session[:comments].try('[]', #comment.id)
The '[]' is in quotes instead of a symbol :[]
Try to use
#myvar = session[:comments][#comment.id]["temp_value"] if session[:comments]