I am writing classes for a SQL Database in Ruby, a few of the query methods are common throughout all my classes so I want to move these methods into a parent class. I can't figure out how to get the original class call to show up in the parent class. Since my classes are the names of my tables, I need them to have access to them in my parent method. I've tried using self.class but that just returns Class, not the actual class I'm using the method on.
Here is the code I want to move into the parent class:
require_relative 'questions_databse.rb'
class User
attr_accessor :id, :fname, :lname
def self.find_by_id(id)
user = QuestionDatabase.instance.execute(<<-SQL, id)
SELECT
*
FROM
users
WHERE
users.id = ?
SQL
user.map { |user| User.new(user) }.first
end
Now what I need to do is something like this:
require_relative 'questions_databse.rb'
require_relative 'modelbase.rb'
class User < ModelBase
attr_accessor :id, :fname, :lname
# no self.find_by_id(id)
Then I want the parent class to do something like this:
require 'active_support/inflector'
class ModelBase
def self.find_by_id(id)
object = QuestionDatabase.instance.execute(<<-SQL, id)
SELECT
*
FROM
#{self.chid_class.name.tableize}
WHERE
#{self.chid_class.name.tableize}.id = ?
SQL
object.map { |object| self.child_class.new(object) }.first
end
end
I have 4 other table classes that I use this method on, so I need to be able to have the code tell exactly what class called it so that the SQL query will run properly.
require 'active_support/inflector'
class ModelBase
def self.find_by_id(id)
p self.class.name
end
end
User.find_by_id(1) #=> "Class"
That is result when I use the self.class.name
I am learning how to code right now and this is the problem that the lesson is giving me. I know there may be easier ways to do this, but I probably haven't learned those yet.
In a class method like your find_by_id:
class ModelBase
def self.find_by_id(id)
p self.class.name
end
end
self is the class itself (so self.class is Class) so you want to look at self.name:
class ModelBase
def self.find_by_id(id)
p name
end
end
Related
This is a question from a rails noob trying to understand concerns and scopes.
I always thought scopes were class methods in rails but then the other day I saw this code from DHH:
module Visible
extend ActiveSupport::Concern`
module ClassMethods
def visible_to(person)
where \
"(#{table_name}.bucket_id IN (?) AND
#{table_name}.bucket_type = 'Project') OR
(#{table_name}.bucket_id IN (?) AND
#{table_name}.bucket_type = 'Calendar')",
person.projects.pluck('projects.id'),
calendar_scope.pluck('calendars.id')
end
end
end
So the way the visible method is used is like so:
current_account.posts.visible_to(current_user)
This is what is confusing me. Self here is a collection of posts so we are acting on instances whereas the visible method seems to be meant to be used as a class method. Isn't david trying to call a class method as a dynamic scope? Could someone please clarify?
Class methods on classes which inherit ActiveRecord::Base can be used also as scopes (on ActiveRecord Relation objects).
Since the module Visible was meant to be mixed into a model which inherits ActiveRecord::Base, its class method visible_to can be used also as a scope.
If this did not clear the issue, you can implement a scope which gets all adult users (age > 20) in the following ways:
class User < ActiveRecord::Base
scope :adult, lambda { where("age > ?", 20) } # with a scope
class << self
def adult # with class method
where("age > ?", 20)
end
end
end
And use it exactly the same with User.adult
I migrated from rails 2.x to 3.x. Now when calling a controller method throws
undefined method `my_helper_method' for nil:NilClass
MyController.rb
class MyController < ApplicationController
def foo
#template.my_helper_method
end
end
MyControllerHelper.rb
class MyControllerHelper
def my_helper_method
puts "Hello"
end
end
ApplicationController
class ApplicationController < ActionController::Base
helper :all
end
How to get this working?
This is actually answered in another SO post: Rails 3: #template variable inside controllers is nil
Essentially, you can replace #template with view_context
#template is an object, in your case nil. If this object doesn't has the method (my_helper_method) in it, you cannot call it (especially not if it is nil).
Methods defined in helpers are called like regular methods. But not in controllers, they are called in views. Your helper :all just makes all helpers available to the views.
So, in your view: my_helper_method :arg1, :arg2
IF you need a method for your object (#template), you need to give your object this method.
Example:
class Template < ActiveRecord::Base
def my_helper_method
# do something on a template instance
end
end
class MyController < ApplicationController
def foo
#template = Template.first
#template.my_helper_method # which actually isn't a helper
end
end
What helpers do:
module MyHelper
def helper_method_for_template(what)
end
end
# in your view
helper_method_for_template(#template)
Mixing in a helper (be aware of having a mess in your code when mixing view helpers with views and models)
class Template < ActiveRecord::Base
include MyHelper
# Now, there is #template.helper_method_for_template(what) in here.
# This can get messy when you are making your helpers available to your
# views AND use them here. So why not just write the code in here where it belongs
# and leave helpers to the views?
end
I want to put logic in the model rather than controller.
class UsersController < ApplicationController
def somemethod
d = User.methodinmodel
end
end
class User < ActiveRecord::Base
def methodinmodel
"retuns foo"
end
end
I get an error that there is no methodinmodel for the User model.
Why?
If you want to be able to call methodinmodel on the User class in general rather than a specific user, you need to make it a class method using self:
class User < ActiveRecord::Base
def self.methodinmodel
"returns foo"
end
end
Your current method definition would only work if you called it on a user:
#user = User.create!
#user.methodinmodel # Works.
User.methodinmodel # Doesn't work.
Using the new implementation using self would allow you to call it like:
User.methodinmodel # Works.
I have the following (simplified model) and wish to access the 'spent' value in the to_json method of the object, ideally as an attribute of the object.
class Task < ActiveRecord::Base
has_many :hours
def spent
self.hours.sum(:spent)
end
end
Is there a way to do this without defining a method and hacking the to_json method? I've been hunting for a way to use scope or by hacking the after_initialize method, but none of these methods provide a 'spent' value when using inspect or to_json on the model.
I need to solve this on models higher up the tree that use a has_many, through relationship too.
You can use the :methods parameter to to_json call.
object.to_json(:methods => :spent)
http://api.rubyonrails.org/classes/ActiveModel/Serializers/JSON.html
The best solution I could find to this was overriding the 'as_json' method to include the attributes that I needed, or to perform the logic required, (in this case the sum of the has_many relationship).
class Task < ActiveRecord::Base
...
def as_json(options = { })
options = {} if options.nil?
self[:job_id] = self.phase.job_id
self[:spent] = self.hours.sum(:spent)
super(options)
end
end
I am trying to create a separate model class for image uploading, which was previously in the object's controller. I also want to make it agnostic, so I can upload images using one class from multiple objects.
In my original object's model class, I have the following now:
class Object < ActiveRecord::Base
after_save :photo_store
delegate :has_photo?, :photo, :photo_path, :store_photo, :photo_filename, :to => :photo_store
def photo_store
PhotoStore.new(self)
end
end
Then, the PhotoStore class looks like this:
class PhotoStore
attr_reader :object
def initialize(object)
#object = object
end
def photo=(file_data)
unless file_data.blank?
#file_data = file_data
self.extension = file_data.original_filename.split('.').last.downcase
end
end
PHOTO_STORE = File.join RAILS_ROOT, 'public', 'photo_store'
def photo_filename
File.join PHOTO_STORE, "#{id}.#{extension}"
end
def photo_path
"/photo_store/#{id}.#{extension}"
end
def has_photo?
File.exists? photo_filename
end
private
def store_photo
if #file_data
FileUtils.mkdir_p PHOTO_STORE
File.open(photo_filename, 'wb') do |f|
f.write(#file_data.read)
end
end
end
end
However, this throws the error below when I try and use the has_photo? method in the object's view.
undefined local variable or method `id' for #
Do I need to put some other type of relationship in place between the Object and PhotoStore?
And a separate question: What's the best way to make this agnostic? Since it uses just the ID of the object, I could just include the Object's name in the filename, but is that the best way to do it?
Thanks!
Because at File.join PHOTO_STORE, "#{id}.#{extension}" you call method PhotoStore#id, but it does not exists.
You should do that
File.join PHOTO_STORE, "#{#object.id}.#{#object.extension}"