I want to print numbers in my rails application with commas. As per the answer here, I could wrap every single number I print with
number_with_delimiter(#number, :delimiter => ',')
However, I don't want to go into my views and apply this manually. I'd much rather override the way integers are printed.
In java/jsp, anything inside a <%= %> tag gets a toString() call to evaluate what is printed on the page, so I figured that overriding the to_s method for the Integer class would do:
class Integer
def to_s
number_with_delimiter(self, :delimiter => ',')
end
end
Unfortunately, this doesn't work in that the numbers printed using the <%=%> tag don't appear with commas. (No errors are raised.)
How do I get this right? Does the <%=%> block not automagically call a to_s method on the given object? How does it evaluate what to print?
You're monkey patching the wrong thing, you want to patch Fixnum. For example:
>> class Fixnum
>> def to_s
>> 'pancakes'
>> end
>> end
=> nil
>> 1.to_s
=> "pancakes"
and for ERB:
>> ERB.new('<%= 11 %>').result
=> "pancakes"
That said, your shortcut (like most shortcuts) will probably end up causing you various new and interesting problems elsewhere. You will end up sending '1,000' to something (such as a database or client-side JavaScript or ...) that expects '1000' and you'll get a confusing hissy fit for your efforts. You'll also have to worry about the other numeric classes such as Float and Bignum.
Fix your views, don't kludge around your own laziness.
Related
i have this big problem, i have a input where i format my amounts like this.
15,550.55, the problem is that once i submit that value it store it as 15.50 because of the BigDecimal Object, it is not taking the whole number.
In my Parameters Im recieving that value as "dr_business_remuneration"=>"15,550.55"
The type of data in my postgresql DB is Numeric(19,2) for that attribute
The only thing i want is that once a submit the value be stored as 15550.55, but be shown in my view as 15,550.55.
i tried with a method in my model with a before_save callback, that erase my "," before saving that value.
before_save: montos_formateados
def montos_formateados
if !self.dr_business_remuneration.blank?
self.dr_business_remuneration.sub(",", "").to_f
end
end
but returns this error.
no implicit conversion of String into Integer
There are a few ways to do this. First, if you want it coded to show in terminal correctly, this should work:
'15550.55'.reverse.scan(/.{1,3}/).join(',').reverse
If you're displaying it on a webpage, this is the best:
<%= number_with_delimiter(#number, :delimiter => ',') %>
If you're OK with a few additional dependencies, this is probably the best way:
require 'active_support'
require 'active_support/core_ext/numeric/conversions'
number = 15550.55
number.to_s(:delimited) # => "12,345"
number.to_s(:delimited) # => "12,345.6789"
I hope that helps!
I have a Model user with the following method:
def number_with_hyphen
number&.insert(8, "-")
end
When I run it several times in my tests I get the following output:
users(:default).number_with_hyphen
"340909-1234"
(byebug) users(:default).number_with_hyphen
"340909--1234"
(byebug) users(:default).number_with_hyphen
"340909---1234"
(byebug) users(:default).number_with_hyphen
"340909----1234"
It changes the number ?Here are the docs https://apidock.com/ruby/v1_9_3_392/String/insert
When I restructure my method to:
def number_with_hyphen
"#{number}".insert(8, "-") if number
end
If works like expected. The output stays the same!
How would you structure the code, how would you perform the insert?
which method should I use instead. Thanks
If you're using the insert method, which in the documentation explicitly states "modifies str", then you will need to avoid doing this twice, rendering it idempotent, or use another method that doesn't mangle data.
One way is a simple regular expression to extract the components you're interested in, ignoring any dash already present:
def number_with_hyphen
if (m = number.match(/\A(\d{8})\-?(\d+)\z/))
[ m[1], m[2] ].join('-')
else
number
end
end
That ends up being really safe. If modified to accept an argument, you can test this:
number = '123456781234'
number_with_hyphen(number)
# => "12345678-1234"
number
# => "123456781234"
number_with_hyphen(number_with_hyphen(number))
# => "12345678-1234"
number_with_hyphen('1234')
# => "1234"
Calling it twice doesn't mangle anything, and any non-conforming data is sent through as-is.
Do a clone of the string:
"#{number}".clone.insert(8, '-')
I am learning rails and going back to ruby to understand how methods in rails (and ruby really work). When I see method calls like:
validates :first_name, :presence => true
I get confused. How do you write methods in ruby that accept symbols or hashes. The source code for the validates method is confusing too. Could someone please simplify this topic of using symbols as arguments in ruby class and instance methods for me?
UPDATE:
Good one #Dave! But What I was trying out was something like:
def full_name (:first_name, :last_name)
#first_name = :first_name
#last_name = :last_name
p "#{#first_name} #{last_name}"
end
full_name("Breta", "Von Sustern")
Which obviously raises errors. I am trying to understand: Why is passing symbols like this as arguments wrong if symbols are just like any other value?
Symbols and hashes are values like any other, and can be passed like any other value type.
Recall that ActiveRecord models accept a hash as an argument; it ends up being similar to this (it's not this simple, but it's the same idea in the end):
class User
attr_accessor :fname, :lname
def initialize(args)
#fname = args[:fname] if args[:fname]
#lname = args[:lname] if args[:lname]
end
end
u = User.new(:fname => 'Joe', :lname => 'Hacker')
This takes advantage of not having to put the hash in curly-brackets {} unless you need to disambiguate parameters (and there's a block parsing issue as well when you skip the parens).
Similarly:
class TestItOut
attr_accessor :field_name, :validations
def initialize(field_name, validations)
#field_name = field_name
#validations = validations
end
def show_validations
puts "Validating field '#{field_name}' with:"
validations.each do |type, args|
puts " validator '#{type}' with args '#{args}'"
end
end
end
t = TestItOut.new(:name, presence: true, length: { min: 2, max: 10 })
t.show_validations
This outputs:
Validating field 'name' with:
validator 'presence' with args 'true'
validator 'length' with args '{min: 2, max: 10}'
From there you can start to see how things like this work.
I thought I'd add an update for Ruby 2+ since this is the first result I found for 'symbols as arguments'.
Since Ruby 2.0.0 you can also use symbols when defining a method. When calling the method these symbols will then act almost the same as named optional parameters in other languages. See example below:
def variable_symbol_method(arg, arg_two: "two", arg_three: "three")
[arg, arg_two, arg_three]
end
result = variable_symbol_method :custom_symbol, arg_three: "Modified symbol arg"
# result is now equal to:
[:custom_symbol, "two", "Modified symbol arg"]
As shown in the example, we omit arg_two: when calling the method and in the method body we can still access it as variable arg_two. Also note that the variable arg_three is indeed altered by the function call.
In Ruby, if you call a method with a bunch of name => value pairs at the end of the argument list, these get automatically wrapped in a Hash and passed to your method as the last argument:
def foo(kwargs)
p kwargs
end
>> foo(:abc=>"def", 123=>456)
{:abc=>"def", 123=>456}
>> foo("cabbage")
"cabbage"
>> foo(:fluff)
:fluff
There's nothing "special" about how you write the method, it's how you call it. It would be perfectly legal to just pass a regular Hash object as the kwargs parameter. This syntactic shortcut is used to implement named parameters in an API.
A Ruby symbol is just a value as any other, so in your example, :first_name is just a regular positional argument. :presence is a symbol used as a Hash key – any type can be used as a Hash key, but symbols are a common choice because they're immutable values.
I think all replies have missed the point of question; and the fact it is asked by someone who is - I guess - not clear on what a symbol is ?
As a newcomer to Ruby I had similar confusions and to me an answer like following would have made more sense
Method Arguments are local variables populated by passed in values.
You cant use symbols as Arguments by themselves, as you cant change value of a symbol.
Symbols are not limited to hashes. They are identifiers, without the extra storage space of a string. It's just a way to say "this is ...."
A possible function definition for the validates call could be (just to simplify, I don't know off the top of my head what it really is):
def validates(column, options)
puts column.to_s
if options[:presence]
puts "Found a presence option"
end
end
Notice how the first symbol is a parameter all of its own, and the rest is the hash.
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]
I want to write a function that allows users to match data based on a regexp, but I am concerned about sanitation of the user strings. I know with SQL queries you can use bind variables to avoid SQL injection attacks, but I am not sure if there's such a mechanism for regexps. I see that there's Regexp.escape, but I want to allow valid regexps.
Here is is the sample function:
def tagged?(text)
tags.each do |tag|
return true if text =~ /#{tag.name}/i
end
return false
end
Since I am just matching directly on tag.name is there a chance that someone could insert a Proc call or something to break out of the regexp and cause havoc?
Any advice on best practice would be appreciated.
Interpolated strings in a Regexp are not executed, but do generate annoying warnings:
/#{exit -3}/.match('test')
# => exits
foo = '#{exit -3}'
/#{foo}/.match('test')
# => warning: regexp has invalid interval
# => warning: regexp has `}' without escape
The two warnings seem to pertain to the opening #{ and the closing } respectively, and are independent.
As a strategy that's more efficient, you might want to sanitize the list of tags into a combined regexp you can run once. It is generally far less efficient to construct and test against N regular expressions than 1 with N parts.
Perhaps something along the lines of this:
class Taggable
def tags
#tags
end
def tags=(value)
#tags = value
#tag_regexp = Regexp.new(
[
'^(?:',
#tags.collect do |tag|
'(?:' + tag.sub(/\#\{/, '\\#\\{').sub(/([^\\])\}/, '\1\\}') + ')'
end.join('|'),
')$'
].to_s,
Regexp::IGNORECASE
)
end
def tagged?(text)
!!text.match(#tag_regexp)
end
end
This can be used like this:
e = Taggable.new
e.tags = %w[ #{exit-3} .*\.gif .*\.png .*\.jpe?g ]
puts e.tagged?('foo.gif').inspect
If the exit call was executed, the program would halt there, but it just interprets that as a literal string. To avoid warnings it is escaped with backslashes.
You should probably create an instance of the Regexp class instead.
def tagged?(text)
return tags.any? { |tag| text =~ Regexp.new(tag.name, Regexp::IGNORECASE) }
end