While not always the &quot;best&quot; approach, Rails offers what&#39;s called a [Polymorphic belongs_to association](http://guides.rubyonrails.org/association_basics.html#polymorphic-associations). It prevents you from defining a foreign key in the database because the xxx_id column is referencing an id in one of many possible tables while another column designates the name of that table&#39;s model, but it makes the relationship more explicit in Rails. Also, it restricts the model to only belong to one of the other models, as opposed to belonging to one or more, as it would happen using the setup of multiple foreign keys without some additional db magic.

I am working on an Android app and have a couple strings that I would like to encrypt before sending to a database.  I&#39;d like something that&#39;s secure, easy to implement, will generate the same thing every time it&#39;s passed the same data, and preferably will result in a string that stays a constant length no matter how large the string being passed to it is.  Maybe I&#39;m looking for a hash.

How to hash a string in Android?

Basically what I need is an script that, when provided with a time and a timezone can return the time in another time zone. 

My main issues are:

* Where to get the time offset from GMT from - is there a public database available for this?
* How to also take into consideration the daylight saving time (DST) differences as well.
* How to nicely wrap it all up inside an PHP class - or is there such a class already available?


Convert time and date from one time zone to another in PHP

I did find some questions on SO about Rails associations that are somewhat like my question, but for the life of me I can&#39;t seem to understand how to use `belongs_to` multiple models.

Here&#39;s the *table structure* I intend to have:

    User
     id
    
    Post
     id
     user_id #foreign key; a post belongs to a User aka &quot;Who created this post&quot;
     
    Comment
     id
     user_id #foreign key; a comment belongs to a User aka &quot;Who made this comment&quot;
     post_id #foreign key; a comment belongs to a Post aka &quot;What post this comment is for&quot;

And the *associations*:
   
    User
     has_many :posts
     has_many :comments
     
    Post
     belongs_to :user
     has_many :comments
    
    Comment
     belongs_to :user
     belongs_to :post

Is this the correct approach?

Rails belongs_to many models

I did find some questions on SO about Rails associations that are somewhat like my question, but for the life of me I can't seem to understand how to use <code>belongs_to</code> multiple models.
Here's the table structure I intend to have:
<pre><code class="hljs language-bash">User
 id

Post
 id
 user_id #foreign key; a post belongs to a User aka "Who created this post"
 
Comment
 id
 user_id #foreign key; a comment belongs to a User aka "Who made this comment"
 post_id #foreign key; a comment belongs to a Post aka "What post this comment is for"
</code></pre>
And the associations:
<pre><code class="hljs language-ruby">User
 has_many :posts
 has_many :comments
 
Post
 belongs_to :user
 has_many :comments

Comment
 belongs_to :user
 belongs_to :post
</code></pre>
Is this the correct approach?

I am hosting on a vps, ubuntu 10.04, rails 3, ruby and mysql installed correctly by following some tutorials. If I run `bundle check` or `bundle install` I get the error &#39;-bash: bundle: command not found&#39;. From `gem list --local` I see &#39;bundler (1.0.2, 1.0.0)&#39; is installed.

I don&#39;t know what&#39;s going wrong...

`gem environment` returns:

   

     RubyGems Environment:
      - RUBYGEMS VERSION: 1.3.7
      - RUBY VERSION: 1.8.7 (2010-04-19 patchlevel 253) [i686-linux]
      - INSTALLATION DIRECTORY: /opt/ruby-enterprise-1.8.7-2010.02/lib/ruby/gems/1.8
      - RUBY EXECUTABLE: /opt/ruby-enterprise-1.8.7-2010.02/bin/ruby
      - EXECUTABLE DIRECTORY: /opt/ruby-enterprise-1.8.7-2010.02/bin
      - RUBYGEMS PLATFORMS:
        - ruby
        - x86-linux
      - GEM PATHS:
         - /opt/ruby-enterprise-1.8.7-2010.02/lib/ruby/gems/1.8
         - /root/.gem/ruby/1.8
      - GEM CONFIGURATION:
         - :update_sources =&gt; true
         - :verbose =&gt; true
         - :benchmark =&gt; false
         - :backtrace =&gt; false
         - :bulk_threshold =&gt; 1000
      - REMOTE SOURCES:
         - http://rubygems.org/

and `echo $PATH` returns:

    /opt/myruby/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/bin/gem:/opt/ruby-enterprise-1.8.7-2010.02/lib/ruby/gems/1.8/gems/:/root/.gem/ruby/1.8

and `which gem` returns:

    /usr/bin/gem

`locate bundle` returns:

    /opt/ruby-enterprise-1.8.7-2010.02/lib/ruby/gems/1.8/



Bundler: Command not found

In my experience, getting dates/times right when programming is always fraught with danger and difficulity. 

Ruby and Rails have always eluded me on this one, if only due to the overwhelming number of options; I never have any idea which I should pick.

When I&#39;m using Rails and looking at ActiveRecord datatypes I can find the following
&gt; :datetime, :timestamp, :time, and :date

and have no idea what the differences are or where the gotchas lurk.

What&#39;s the difference? What do you use them for? 

(P.S. I&#39;m using Rails3)

In Ruby on Rails, what&#39;s the difference between DateTime, Timestamp, Time and Date?

rails 3 seems to escape everything, including html.  I have tried using raw() but it still escapes html.  Is there a workaround?  This is my helper that I am using (/helpers/application_helper.rb):

    module ApplicationHelper
      def good_time(status = true)
        res = &quot;&quot;
        if status == true
          res &lt;&lt; &quot;Status is true, with a long message attached...&quot;
        else
          res &lt;&lt; &quot;Status is false, with another long message&quot;
        end
      end
    end

I am calling the helper in my view using this code:

    &lt;%= raw(good_time(true)) %&gt;



Don&#39;t escape html in ruby on rails

I have the following in a controller 

    def update
        @permission = Permission.find_by_user_id(params[:user_id])

But I want it to also find by another param, `project_id` 

How can I do something like this in Rails?


    @permission = Permission.find_by_user_id_and_project_id(params[:user_id],params[:user_id])



Rails - Find By with 2 fields?

I&#39;m trying to do something like this, but it&#39;s not working. How would I do this in Rails 3?

    Student.find(12).includes(:teacher)



How to do find() with includes() in Rails 3

I have used RESTful techniques to generate a model (in fact, I am using Devise gem, which does that for me), and I have added new fields called first_name and last_name to the model. Migration went fine. I added attr_accessor :first_name, :last_name to the model and expected it would just work. But when I try to mass-assign new instances with Doctor.create({:first_name=&gt;&quot;MyName&quot;}) etc., I am getting errors saying I can&#39;t mass-assign protected attributes. 

I thought the whole point of using attr_accessor was to get around the protectedness of the fields of a model. Can you help me make sense of this message?

Edit: oh, and by the way the records do not get created either. I thought they should be since this is just a warning, but they are not on the database.

Edit2: here is my model

    class Doctor &lt; User
      has_many :patients
      has_many :prescriptions, :through=&gt; :patients
    
      validates_presence_of :invitations, :on =&gt; :create, :message =&gt; &quot;can&#39;t be blank&quot;
    
      attr_accessor :invitations
    end

and the schema, which doesn&#39;t have the first_name and last_name because they are created in the users table, which is the ancestor of doctors. I used single table inheritance.

    create_table :doctors do |t|
      t.integer :invitations

      t.timestamps
    end

and this is the migration to change the users table

    add_column :users, :first_name, :string
    add_column :users, :last_name, :string
    add_column :users, :type, :string

EDIT: here is the seed file. I am not including the truncate_db_table method, but it works.

    %w{doctors patients}.each do |m|
      truncate_db_table(m)  
    end  

    Doctor.create(:invitations=&gt;5, :email=&gt;&quot;email@gmail.com&quot;, :first_name=&gt;&quot;Name&quot;, :last_name=&gt;&quot;LastName&quot;)
    Patient.create(:doctor_id=&gt;1, :gender=&gt;&quot;male&quot;, :date_of_birth=&gt;&quot;1991-02-24&quot;)



&quot;WARNING: Can&#39;t mass-assign protected attributes&quot;

In my database has column names such as &#39;delete&#39; or &#39;listen-control&#39; and so on. These cannot be changed, so I would like to alias the names so as to avoid problems in my application.

I found [the following code][1] but it is outdated (05 Aug 2005) and doesn&#39;t work with Rails 3:

    module Legacy
      def self.append_features(base)
        super
        base.extend(ClassMethods)
      end
      module ClassMethods
        def alias_column(options)
          options.each do |new_name, old_name|
            self.send(:define_method, new_name) { self.send(old_name) }
            self.send(:define_method, &quot;#{new_name}=&quot;) { |value| self.send(&quot;#{old_name}=&quot;, value) }
          end
        end
      end
    end
    
    ActiveRecord::Base.class_eval do
      include Legacy
    end

How can I alias the column names? Is it possible?

  [1]: http://snippets.dzone.com/posts/show/556

Alias for column names in Rails

Given the following associations, I need to reference the `Question` that a `Choice` is attached through from the `Choice` model. I have been attempting to use `belongs_to :question, through: :answer` to perform this action.

    class User
      has_many :questions
      has_many :choices
    end

    class Question
      belongs_to :user
      has_many :answers
      has_one :choice, :through =&gt; :answer
    end

    class Answer
      belongs_to :question
    end

    class Choice
      belongs_to :user
      belongs_to :answer
      belongs_to :question, :through =&gt; :answer

      validates_uniqueness_of :answer_id, :scope =&gt; [ :question_id, :user_id ]
    end

I am getting

&gt; NameError uninitialized constant `User::Choice`

when I try to do `current_user.choices`

It works fine, if I don&#39;t include the

    belongs_to :question, :through =&gt; :answer
 
But I want to use that because I want to be able to do the `validates_uniqueness_of`

I am probably overlooking something simple. Any help would be appreciated.

belongs_to through associations

I have a table and I&#39;m trying to add a unique index on two columns. Those columns are also indexed. So my question is if I just can remove the indexes who were just for one column or if I have to use all three indexes:

    add_index &quot;subscriptions&quot;, [&quot;user_id&quot;]
    add_index &quot;subscriptions&quot;, [&quot;content_id&quot;]
    add_index &quot;subscriptions&quot;, [&quot;user_id&quot;], [&quot;content_id&quot;], :unique =&gt; true


How to implement a unique index on two columns in rails

For normal columns, you can get at them via the `columns` class method. However, associations may be named something quite different if the `foreign_key` option is set in the relationship method. For example, given

    class Post
      has_many :comments, :foreign_key =&gt; :message_id # this is a contrived example
    end

if I did `Post.column_names` I could get at `message_id`, but is there any way to get `comments`?


How to get activerecord associations via reflection

I have been getting all kinds of conflicting information regarding this basic question, and the answer is pretty crucial to my current problems. So, very simply, in Rails 3, is it allowed or not allowed to use accepts_nested_attributes_for with a belongs_to relationship?

    class User &lt; ActiveRecord::Base
      belongs_to :organization
      accepts_nested_attributes_for :organization
    end

    class Organization &lt; ActiveRecord::Base
      has_many :users
    end

In a view:

    = form_for @user do |f|
      f.label :name, &quot;Name&quot;
      f.input :name
      
      = f.fields_for :organization do |o|
        o.label :city, &quot;City&quot;
        o.input :city
    
      f.submit &quot;Submit&quot;

Does accepts_nested_attributes_for work with belongs_to?

I have been (hours) trouble with associations in Rails. I found a lot of similar problems, but I couldn&#39;t apply for my case:

City&#39;s class:

    class City &lt; ApplicationRecord
      has_many :users
    end

User&#39;s class:

    class User &lt; ApplicationRecord
      belongs_to :city
      
      validates :name, presence: true, length: { maximum: 80 }
      validates :city_id, presence: true
    end

Users Controller:

    def create
        Rails.logger.debug user_params.inspect
        @user = User.new(user_params)
        if @user.save!
          flash[:success] = &quot;Works!&quot;
          redirect_to &#39;/index&#39;
        else
          render &#39;new&#39;
        end
     end

    def user_params
      params.require(:user).permit(:name, :citys_id)
    end

Users View:

    &lt;%= form_for(:user, url: &#39;/user/new&#39;) do |f| %&gt;
      &lt;%= render &#39;shared/error_messages&#39; %&gt;

      &lt;%= f.label :name %&gt;
      &lt;%= f.text_field :name %&gt;
      
      &lt;%= f.label :citys_id, &quot;City&quot; %&gt;
      &lt;select name=&quot;city&quot;&gt;
        &lt;% @city.all.each do |t| %&gt;
          &lt;option value=&quot;&lt;%= t.id %&gt;&quot;&gt;&lt;%= t.city %&gt;&lt;/option&gt;
        &lt;% end %&gt;
      &lt;/select&gt;
    end

Migrate:

    class CreateUser &lt; ActiveRecord::Migration[5.0]
      def change
        create_table :user do |t|
          t.string :name, limit: 80, null: false
          t.belongs_to :citys, null: false
          t.timestamps
      end
    end

Message from console and browser:

    ActiveRecord::RecordInvalid (Validation failed: City must exist):


Well, the problem is, the attributes from User&#39;s model that aren&#39;t FK they are accept by User.save method, and the FK attributes like citys_id are not. Then it gives me error message in browser saying that &quot;Validation failed City must exist&quot;.

Thanks



Content Type	Original Author	Original Content on Stackoverflow
Question	Zabba	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Maxem	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	Zhenya Slabkovski	View Answer on Stackoverflow

Rails belongs_to many models

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

Convert time and date from one time zone to another in PHP

How to hash a string in Android?

Attributions