An ActiveRecord object lifecycle:

1.**new record**

    item = Item.new
    item.new_record? #=&gt; true

2.**persisted**

    item.save
    item.persisted? #=&gt; true

3.**changed**

    item.name = &quot;other&quot;
    item.changed? #=&gt; true

4.**destroyed**

    item.destroy
    item.destroyed? #=&gt; true




[`#new_record?`](http://apidock.com/rails/ActiveRecord/Persistence/new_record%3F) does just that:
  
    object.new_record?

I want to understand the basic differences clearly between Javascript object and JSON string.

Let&#39;s say I create the following JS variable:

    var testObject = {one: 1,&quot;two&quot;:2,&quot;three&quot;:3};

**Q1. Is the key/property name valid both with/without quotes?** (e.g. `&quot;one&quot; : 1`) 

If yes, what is the difference?

**Q2: If I convert the above object using `JSON.stringify(testObject)`, what’s the difference between the original JS object and the JSON?** 

I feel they are almost the same. Please elaborate on this.

**Q3: For parsing a JSON string, is the method below recommended?**

    var javascriptObj = JSON.parse(jSonString);

Javascript object Vs JSON

In Eclipse, I&#39;ve created a project from a source and now it shows errors - &quot;R cannot be resolved to a variable&quot;. From what I found here, I had cleared and rebuilt the project, but still the R file doesn&#39;t appear in the /gen folder.

Any ideas?

&quot;R cannot be resolved to a variable&quot;?

How can I check if an `ActiveRecord` object is new or is already persisted?

Determine if ActiveRecord Object is New

<p>How can I check if an <code>ActiveRecord</code> object is new or is already persisted?</p>


There is all sorts of talk lately in the Ruby on Rails community about [decorators][1] and presenters.

What is the essential difference between the two? If there is, what are the clues that tell me which one to use over the other? Or perhaps to use the two in conjunction?

  [1]: https://en.wikipedia.org/wiki/Decorator_pattern


Ruby on Rails patterns - decorator vs presenter

I&#39;m confused on how to generate a model that belongs_to another model. My book uses this syntax to associate Micropost with User:

    rails generate model Micropost user_id:integer

but https://guides.rubyonrails.org/active_record_migrations.html#creating-a-standalone-migration says to do it like this:

    rails generate model Micropost user:references

The migrations generated by these 2 are different. Also, for the former, how does rails know that `user_id` is a foreign key referencing `user`? Thanks!

Generate model in Rails using user_id:integer vs user:references

I have installed PostgreSQL on my Mac OS Lion, and am working on a rails app. I use RVM to keep everything separate from my other Rails apps.

For some reason when I try to migrate the db for the first time rake cannot find the postgres user. I get the error

     FATAL:  role &quot;postgres&quot; does not exist

I have pgAdmin so I can clearly see there is a postgres user in the DB - the admin account in fact - so I&#39;m not sure what else to do.

I read somewhere about people having issues with PostgreSQL because of which path it was installed in, but then I don&#39;t think I would have gotten that far if it couldn&#39;t find the db.

Rails and PostgreSQL: Role postgres does not exist

I need validate some attributes ONLY if they are not empty. 

For example the user may have a logo. If we try to load it - validation should work. If we simply update the user&#39;s data without the logo, validation must be skipped.

Now i have:

The form has a choice of two files. One - logo, second - avatar.
Both of this attributes is part of User model. In User model a have validation:

    validates_preference_of :logo_file_name, :message=&gt;I18n.t(&quot;...&quot;)
    validates_format_of :logo_file_name, :with=&gt;/\.(jpeg|jpg|png|gif)$/i, :message=&gt; I18n.t(&quot;...&quot;)
    validates_preference_of :avatar_file_name, :message=&gt;I18n.t(&quot;...&quot;)
    validates_format_of :avatar_file_name, :with=&gt;/\.(jpeg|jpg|png|gif)$/i, :message=&gt; I18n.t(&quot;...&quot;)

In this case, if we try to create a new User without selected logo and avatar, we will have errors (our validation). I tryed change validation and add &quot;:on =&gt; :update&quot; like this:

    validates_preference_of :logo_file_name, :message=&gt;I18n.t(&quot;...&quot;), :on =&gt; :update
    validates_format_of :logo_file_name, :with=&gt;/\.(jpeg|jpg|png|gif)$/i, :message=&gt; I18n.t(&quot;...&quot;), :on =&gt; :update
    validates_preference_of :avatar_file_name, :message=&gt;I18n.t(&quot;...&quot;), :on =&gt; :update
    validates_format_of :avatar_file_name, :with=&gt;/\.(jpeg|jpg|png|gif)$/i, :message=&gt; I18n.t(&quot;...&quot;), :on =&gt; :update

Now i can create user without selected logo and avatar, but if i try edit user and try upload only logo - i have validation errors of avatar. If i choose file for avatar and logo leave blank - i have validation errors for logo.

How i can run validation ony for attribute that I want to change?

Validate attribute only if it present (only if user fill in it)

I keep getting conflicting opinions on the practice of storing information in the `Thread.current` hash (e.g., the current_user, the current subdomain, etc.). The technique has been proposed as a way to simplify later processing within the model layer (query scoping, auditing, etc.). 

 - https://stackoverflow.com/questions/4217911/why-are-my-thread-variables-intermittent-in-rails
 - https://stackoverflow.com/questions/7509883/alternative-to-using-thread-current-in-api-wrapper-for-rails
 - https://stackoverflow.com/questions/6659221/are-thread-current-values-and-class-level-attributes-safe-to-use-in-rails

Many consider the practice unacceptable because it breaks the MVC pattern.
Others express concerns about reliability/safety of the approach, and my 2-part question focuses on the latter aspect.

1. Is the `Thread.current` hash guaranteed to be available and private to one and only one response, throughout its entire cycle?

2. I understand that a thread, at the end of a response, may well be handed over to other incoming requests, thereby leaking any information stored in `Thread.current`. Would clearing such information before the end of the response (e.g. by executing `Thread.current[:user] = nil` from a controller&#39;s `after_filter`) suffice in preventing such security breach?

Thanks!
Giuseppe

Safety of Thread.current[] usage in rails

How can you combine 2 different conditions using logical OR instead of AND?

**NOTE:** 2 conditions are generated as rails scopes and can&#39;t be easily changed into something like `where(&quot;x or y&quot;)` directly.

Simple example:

    admins = User.where(:kind =&gt; :admin)
    authors = User.where(:kind =&gt; :author)

It&#39;s easy to apply AND condition (which for this particular case is meaningless):

    (admins.merge authors).to_sql
    #=&gt; select ... from ... where kind = &#39;admin&#39; AND kind = &#39;author&#39;

But how can you produce the following query having 2 different Arel relations already available?

    #=&gt; select ... from ... where kind = &#39;admin&#39; OR kind = &#39;author&#39;


It seems ([according to Arel readme][1]):

&gt; The OR operator is not yet supported


But I hope it doesn&#39;t apply here and expect to write something like:

    (admins.or authors).to_sql

  [1]: https://github.com/nkallen/arel

ActiveRecord Arel OR condition

I want to get all records where the created_at field is less than today (a date).
Is there anything like: 

    MyTable.find_by_created_at(&lt; 2.days.ago)


Active Record - Find records which were created_at before today

If I do 

    widget = Widget.find_or_create_by_widgetid(:widgetid =&gt; &quot;12345&quot;, :param2 =&gt; &quot;folk&quot;) 

etc. then how do I tell if newobj is a found or newly created Widget? Is there something I can test conditionally on `widget` that will tell me?

Rails ActiveRecord: How do I know if find_or_create_by found or created?

I have a model named `Song`. I also have a model named `Listen`. A `Listen` `belongs_to :song`, and a song `:has_many listens` (can be listen to many times).

In my model I want to define a method `self.top` which should return the top 5 songs listened to the most. How can I achieve that using the `has_many` relation?

I&#39;m using Rails 3.1.

Thanks!

Rails 3 ActiveRecord: Order by count on association

I am trying to do a query in in Rails with ActiveRecord that specifies some condition on a joined table. And i can&#39;t seem to get it to work, even though i follow the examples from here:

http://guides.rubyonrails.org/active_record_querying.html#specifying-conditions-on-the-joined-tables

From the [guides][1]:

&gt; `Client.joins(:orders).where(:orders =&gt; {:created_at =&gt; time_range})`

My database schema looks like this, with tables `scores`, `submissions` and `tasks`:


      create_table &quot;scores&quot;, :force =&gt; true do |t|
        t.integer  &quot;value&quot;
        t.integer  &quot;user_id&quot;
        t.datetime &quot;created_at&quot;
        t.datetime &quot;updated_at&quot;
      end

      add_index &quot;scores&quot;, [&quot;user_id&quot;], :name =&gt; &quot;index_scores_on_user_id&quot;

      create_table &quot;submissions&quot;, :force =&gt; true do |t|
        t.integer  &quot;user_id&quot;
        t.integer  &quot;task_id&quot;
        t.integer  &quot;score_id&quot;
        t.datetime &quot;completed_at&quot;
        t.datetime &quot;created_at&quot;
        t.datetime &quot;updated_at&quot;
      end

      add_index &quot;submissions&quot;, [&quot;score_id&quot;], :name =&gt; &quot;index_submissions_on_score_id&quot;
      add_index &quot;submissions&quot;, [&quot;task_id&quot;], :name =&gt; &quot;index_submissions_on_task_id&quot;
      add_index &quot;submissions&quot;, [&quot;user_id&quot;], :name =&gt; &quot;index_submissions_on_user_id&quot;

      create_table &quot;tasks&quot;, :force =&gt; true do |t|
        t.integer  &quot;episode_id&quot;
        t.integer  &quot;score&quot;
        t.string   &quot;key&quot;
        t.datetime &quot;created_at&quot;
        t.datetime &quot;updated_at&quot;
      end

So i want to do a query where I can find all &quot;scores&quot; that have a relation to a spesific task. Submission belongs to tasks and scores.

My query now looks like this:

    Score.joins(:submission).where(:submission =&gt; {:task_id =&gt; 1})

This generates the following syntax:

    SELECT &quot;scores&quot;.* FROM &quot;scores&quot; INNER JOIN &quot;submissions&quot; ON &quot;submissions&quot;.&quot;score_id&quot; = &quot;scores&quot;.&quot;id&quot; WHERE &quot;submission&quot;.&quot;task_id&quot; = 1

Which generates the following error:

    SQLite3::SQLException: no such column: submission.task_id

But there is a column `submission.task_id`, which you can see in the db schema. And i can do this successfully:

    SELECT &quot;submissions&quot;.* FROM &quot;submissions&quot; WHERE &quot;submissions&quot;.&quot;task_id&quot; = 1


  [1]: http://guides.rubyonrails.org

Content Type	Original Author	Original Content on Stackoverflow
Question	jrhicks	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Damien	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	John Beynon	View Answer on Stackoverflow

Determine if ActiveRecord Object is New

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

"R cannot be resolved to a variable"?

Javascript object Vs JSON

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