I am trying to build a ruby on rails and graphQL app, and am working on a user update mutation. I have spent a long time trying to figure it out, and when I accidentally made a typo, it suddenly worked.
The below is the working migration:
module Mutations
class UpdateUser < BaseMutation
argument :id, Int
argument :first_name, String
argument :last_name, String
argument :username, String
argument :email, String
argument :password, String
field :user, Types::User
field :errors, [String], null: false
def resolve(id:, first_name:, last_name:, username:, email:, password:)
user = User.find(id)
user.update(first_name:, last_name:, username:, email:, password:)
{ user:, errors: [] }
rescue StandardError => e
{ user: nil, errors: [e.message] }
end
end
end
The thing I am confused about is when I define the arguments, they are colon first: eg :id or :first_name
When I pass them to the resolve method they only work if they have the colon after: eg id: or first_name:
When I pass the variables to the update method, they use the same syntax of colon after, for all variables other than ID. For some reason, when I used id: it was resolving to a string "id", and using colon first :id was returning an undefined error.
It is only when I accidentally deleted the colon, and tried id that it actually resolved to the passed through value.
My question for this, is why and how this is behaving this way? I have tried finding the answer in the docs, and reading other posts, but have been unable to find an answer.
Please someone help my brain get around this, coming from a PHP background, ruby is melting my brain.
It's going to take some time to get used to Ruby, coming from PHP, but it won't be too bad.
Essentially id is a variable, or object/model attribute when used like model_instance.id. In PHP this would be like $id or $object_instance->id.
When you see id: it is the key in a key-value pair, so it expects something (a value) after it (or assumes nil if nothing follows, often in method definitions using keyword arguments like your example). A typical use might be model_instance.update(id: 25) where you are essentially passing in a hash to the update method with id as the key and 25 as the value. The older way to write this in Ruby is with a "hash rocket" like so: model_instance.update(:id => 25).
More reading on Ruby hashes: https://www.rubyguides.com/2020/05/ruby-hash-methods
More reading on keyword arguments: https://www.rubyguides.com/2018/06/rubys-method-arguments
Now if you're paying attention that hash rocket now uses the 3rd type you're asking about. When you see a colon preceding a string like that it is called a "symbol" and it will take some time to get used to them but they are essentially strings in Ruby that are one character fewer to define (and immutable). Instead of using 'id' or "id" as a string, Ruby folks often like to use :id as a symbol and it will typically auto-convert to a string when needed. A good example might be an enumerator of sorts.
state = :ready
if state == :ready
state = :finished
else
state = :undefined
end
More reading on Ruby symbols: https://www.rubyguides.com/2018/02/ruby-symbols
Related
I'm using Toptal's Chewy gem to connect and query my Elasticsearch, just like an ODM.
I'm using Chewy along with Elasticsearch 6, Ruby on Rails 5.2 and Active Record.
I've defined my index just like this:
class OrdersIndex < Chewy::Index
define_type Order.includes(:customer) do
field :id, type: "keyword"
field :customer do
field :id, type: "keyword"
field :name, type: "text"
field :email, type: "keyword"
end
end
end
And my model:
class Order < ApplicationRecord
belongs_to :customer
end
The problem here is that when I perform any query using Chewy, the customer data gets deserialized as a hash instead of an Object, and I can't use the dot notation to access the nested data.
results = OrdersIndex.query(query_string: { query: "test" })
results.first.id
# => "594d8e8b2cc640bb78bd115ae644637a1cc84dd460be6f69"
results.first.customer.name
# => NoMethodError: undefined method `name' for #<Hash:0x000000000931d928>
results.first.customer["name"]
# => "Frederique Schaefer"
How can I access the nested association using the dot notation (result.customer.name)? Or to deserialize the nested data inside an Object such as a Struct, that allows me to use the dot notation?
try to use
results = OrdersIndex.query(query_string: { query: "test" }).objects
It converts query result into active record Objects. so dot notation should work. If you want to load any extra association with the above result you can use .load method on Index.
If you want to convert existing ES nested object to accessible with dot notation try to reference this answer. Open Struct is best way to get things done in ruby.
Unable to use dot syntax for ruby hash
also, this one can help too
see this link if you need openStruct to work for nested object
Converting the just-deserialized results to JSON string and deserializing it again with OpenStruct as an object_class can be a bad idea and has a great CPU cost.
I've solved it differently, using recursion and the Ruby's native Struct, preserving the laziness of the Chewy gem.
def convert_to_object(keys, values)
schema = Struct.new(*keys.map(&:to_sym))
object = schema.new(*values)
object.each_pair do |key, value|
if value.is_a?(Hash)
object.send("#{key}=", convert_to_object(value.keys, value.values))
end
end
object
end
OrdersIndex.query(query_string: { query: "test" }).lazy.map do |item|
convert_to_object(item.attributes.keys, item.attributes.values)
end
convert_to_object takes an array of keys and another one of values and creates a struct from it. Whenever the class of one of the array of values items is a Hash, then it converts to a struct, recursively, passing the hash keys and values.
To presence the laziness, that is the coolest part of Chewy, I've used Enumerator::Lazy and Enumerator#map. Mapping every value returned by the ES query into the convert_to_object function, makes every entry a complete struct.
The code is very generic and works to every index I've got.
I have a DI routine where I have a large csv I'm importing with known column format. I first set up a column map:
col_map =
{
4 => :name,
6 => :description,
21 => :in_stock,
...
I then read each line in, and then using the column map, attempt to set the attribute:
i = Item.new
col_map.each do |k,v|
i[v] = chunks[k] #chunks is the line read in split by the delimiter
In my item declaration, I declare two attributes, b/c these are not stored in the database, they're used for other logic:
attr_writer :in_stock
attr_writer :end_date
When the code gets to this line:
i[v] = chunks[k]
I get this message:
X.DEPRECATION WARNING: You're trying to create an attribute `in_stock'. Writing arbitrary attributes on a model is deprecated. Please just use `attr_writer`
But I'm not trying to create an attribute, and I am using attr_writer. I suspect this has something to do with the [] I'm using instead of . for the lvalue.
Can anyone see what I'm doing wrong?
Thanks for any help,
Kevin
Admittedly, the deprecation wording is slightly confusing, but you're seeing this warning because the model[attribute_name] = ... style is only supported for ActiveRecord attributes on the model, not non-persisted attributes added with attr_writer.
You can see the code that produces the warning over here.
To address this I'd use send which will work for all attributes e.g.
i.send("#{v}=", chunks[k])
I'm playing around with Netflix's Workflowable gem. Right now I'm working on making a custom action where the user can choose choices.
I end up pulling {"id":1,"value":"High"} out with #options[:priority][:value]
What I want to do is get the id value of 1. Any idea how to pull that out? I tried #options[:priority][:value][:id] but that seems to through an error.
Here's what the action looks like/how I'm logging the value:
class Workflowable::Actions::UpdateStatusAction < Workflowable::Actions::Action
include ERB::Util
include Rails.application.routes.url_helpers
NAME="Update Status Action"
OPTIONS = {
:priority => {
:description=>"Enter priority to set result to",
:required=>true,
:type=>:choice,
:choices=>[{id: 1, value: "High"} ]
}
}
def run
Rails.logger.debug #options[:priority][:value]
end
end
Here's the error:
Error (3a7b2168-6f24-4837-9221-376b98e6e887): TypeError in ResultsController#flag
no implicit conversion of Symbol into Integer
Here's what #options[:priority] looks like:
{"description"=>"Enter priority to set result to", "required"=>true, "type"=>:choice, "choices"=>[{"id"=>1, "value"=>"High"}], "value"=>"{\"id\":1,\"value\":\"High\"}", "user_specified"=>true}
#options[:priority]["value"] looks to be a strong containing json, not a hash. This is why you get an error when using [:id] (this method doesn't accept symbols) and why ["id"] returns the string "id".
You'll need to parse it first, for example with JSON.parse, at which point you'll have a hash which you should be able to access as normal. By default the keys will be strings so you'll need
JSON.parse(value)["id"]
I'm assuming the error is something like TypeError: no implicit conversion of Symbol into Integer
It looks like #options[:priority] is a hash with keys :id and :value. So you would want to use #options[:priority][:id] (lose the :value that returns the string).
I just started learning ruby on rails, and I'm wondering when I should use "=>" and when I should use "=" for assignment. I am seeing that you use "=>" for hash, for assigning values to symbols in migrations, but i'm not sure where to draw the line.
Thanks!
The => symbol is used solely for hashes. Ruby has a feature in which hashes can be passed as the last argument to a method call without including the surrounding braces. This provides something that resembles keyword arguments (though until Ruby 2.0, Ruby didn't have keyword arguments).
So when you see this:
t.integer :foo, :default => 5
What it really means is this:
t.integer(:foo, { :default => 5 })
The rest is just syntactic sugar designed to make it look nicer.
The = symbol, on the other hand, is the assignment operator you know and love from nearly any programming language.
I struggled with this for a while, but now prefer to use the new style for hashes wherever possible
t.integer :foo, default: 5
t.string :bar, default: 'Dave'
=> is not the same as assignment, but I can see why it is confusing. In a hash you create a key and a value as a pair. The key and value can be anything
{'key1' => 'some value', :symbol_key => 'other value'}
This is different to the assignment, which you can see clearly because if you want the above hash to remain available to your program, you either have to pass it to a method or assign it to a variable
myhash = {'key1' => 'some value', :symbol_key => 'other value'}
And only now can you retrieve stuff from your hash
puts myhash['key1']
So the => operator is actually used to construct hashes (or dictionary objects), assignment allows you to store values in the program.
What is happening quite commonly Rails (and therefore in migrations), is that the hash is being created and passed to the method call without you realising it. But the plumbing is still the same, it's still only a hash that is created.
In Ruby 1.9 you can now define hashes using a javascript-like syntax, so you might start seeing this as well.
myhash = {key1: 'some value', key2: 'other value'}
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.