ActiveRecord&#39;s `new_record?` method returns `true` if the object hasn&#39;t been saved yet.

 - [new_record? documentation][1]


  [1]: http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M001843

you can use post.persisted? as well, if it return false means record in new

&lt;a href=&quot;http://apidock.com/rails/ActiveRecord/Persistence/persisted%3F&quot;&gt; persisted?&lt;/a&gt;

Is there any convenient way to read and parse data from incoming request.

E.g client initiate post request

    URLConnection connection = new URL(url).openConnection();
    connection.setDoOutput(true);
    connection.setRequestProperty(&quot;Content-Type&quot;, &quot;multipart/form-data; boundary=&quot; + boundary);
    PrintWriter writer = null;
    try {
        OutputStream output = connection.getOutputStream();
        writer = new PrintWriter(new OutputStreamWriter(output, charset), true); // true = autoFlush, important!
        // Send normal param.
        writer.println(&quot;--&quot; + boundary);
        writer.println(&quot;Content-Disposition: form-data; name=\&quot;param\&quot;&quot;);
        writer.println(&quot;Content-Type: text/plain; charset=&quot; + charset);
        writer.println();
        writer.println(param);

I’m not able to get param using `request.getParameter(&quot;paramName&quot;)`. The following code

    BufferedReader reader = new BufferedReader(new InputStreamReader(
        request.getInputStream()));
      StringBuilder sb = new StringBuilder();
      for (String line; (line = reader.readLine()) != null;) {
       System.out.println(line);
    
      }

however displays the content for me 

    -----------------------------29772313742745
    Content-Disposition: form-data; name=&quot;name&quot;
    J.Doe
    -----------------------------29772313742745
    Content-Disposition: form-data; name=&quot;email&quot;
    abuse@spamcop.com
    -----------------------------29772313742745

What is the best way to parse incoming request? I don’t want to write my own parser, probably there is a  ready solution.





Convenient way to parse incoming multipart/form-data parameters in a Servlet

I&#39;m a solo developer, working in a local Git repository. For backups, I want to send an exact copy of that repository off to another server.

Is it sufficient to do this?

    git push --mirror

I&#39;m asking because I can sometimes run this command two or three times before Git tells me &quot;Everything up-to-date&quot;, so apparently it&#39;s not an exact mirror. It seems to be re-pushing tracking branches...?

    $ git push --mirror
    Counting objects: 42, done.
    Delta compression using up to 8 threads.
    Compressing objects: 100% (30/30), done.
    Writing objects: 100% (30/30), 5.09 KiB, done.
    Total 30 (delta 17), reused 0 (delta 0)
    To ssh://my/repo/url
       c094a10..0eedc92  mybranch -&gt; mybranch
    $ git push --mirror
    Total 0 (delta 0), reused 0 (delta 0)
    To ssh://my/repo/url
       c094a10..0eedc92  origin/mybranch -&gt; origin/mybranch
    $ git push --mirror
    Everything up-to-date

What is happening, and is this a good strategy?

Edit: I don&#39;t like to use something like `git bundle` or `.tar.bz2` archives, because I&#39;d like the backup to be an accessible working copy. Since my backup server is connected to the net and always on, this is a nice way to access the repository when I&#39;m on the road.

Is &quot;git push --mirror&quot; sufficient for backing up my repository?

    class Post &lt; ActiveRecord::Base
    end
    
    post = Post.new

How do I judge whether the &#39;post&#39; is a new model which is not pulled from the database? 







How to know whether a model is new or not?

<pre><code class="hljs language-arduino">class Post &#x3C; ActiveRecord::Base
end

post = Post.new
</code></pre>
How do I judge whether the 'post' is a new model which is not pulled from the database?

I want to create a new rails application and fire up the rails server for that application, everything from a ruby script.

My code look like this:

    #!/usr/bin/env ruby
    system &quot;rails new my_app&quot;
    system &quot;cd my_app&quot;
    system &quot;rails server &amp;&quot;

However, when running &quot;rails server &amp;&quot; the path is not in the my_app folder, but in the parent folder.

Is there a way to change directory inside a script so that i can run &quot;rails server&quot;, &quot;rake about&quot; and &quot;rake db:migrate&quot; for that new application?

All work around tips would be appreciated.

To change directory inside a ruby script?

I have an array `@horses = []` that I fill with some random horses.

How can I check if my `@horses` array includes a horse that is already included (exists) in it?

I tried something like:

    @suggested_horses = []
      @suggested_horses &lt;&lt; Horse.find(:first,:offset=&gt;rand(Horse.count))
      while @suggested_horses.length &lt; 8
        horse = Horse.find(:first,:offset=&gt;rand(Horse.count))
        unless @suggested_horses.exists?(horse.id)
           @suggested_horses&lt;&lt; horse
        end
      end

I also tried with `include?` but I saw it was for strings only. With `exists?` I get the following error:

    undefined method `exists?&#39; for #&lt;Array:0xc11c0b8&gt;

So the question is how can I check if my array already has a &quot;horse&quot; included so that I don&#39;t fill it with the same horse?


How do I check to see if my array includes an object?

I&#39;m making a new web app using Rails, and was wondering, what&#39;s the difference between `string` and `text`? And when should each be used?

Difference between string and text in rails?

Since the latest Rails 3 release is not auto-loading modules and classes from lib anymore,
what would be the best way to load them?

From github:

&gt;     A few changes were done in this commit:
&gt;     
&gt;     Do not autoload code in *lib* for applications (now you need to explicitly 
&gt;     require them). This makes an application behave closer to an engine 
&gt;     (code in lib is still autoloaded for plugins);

Best way to load module/class from lib folder in Rails 3?

Below is an error, caused by a form in my Rails application:

    Processing UsersController#update (for **ip** at 2010-07-29 10:52:27) [PUT]
      Parameters: {&quot;commit&quot;=&gt;&quot;Update&quot;, &quot;action&quot;=&gt;&quot;update&quot;, &quot;_method&quot;=&gt;&quot;put&quot;, &quot;authenticity_token&quot;=&gt;&quot;ysiDvO5s7qhJQrnlSR2+f8jF1gxdB7T9I2ydxpRlSSk=&quot;, **more parameters**}
    
    ActionController::InvalidAuthenticityToken (ActionController::InvalidAuthenticityToken):

This happens for every non-`get` request and, as you see, `authenticity_token` is there.


ActionController::InvalidAuthenticityToken

Can someone please tell me what

    send(&quot;#{Model.find...}&quot;)

is and does?

What does send() do in Ruby?

I have two arrays

    a = [:foo, :bar, :baz, :bof]

and

    b = [&quot;hello&quot;, &quot;world&quot;, 1, 2]

I want

    {:foo =&gt; &quot;hello&quot;, :bar =&gt; &quot;world&quot;, :baz =&gt; 1, :bof =&gt; 2}

Any way to do this?

How to build a Ruby hash out of two equally-sized arrays?

I installed RVM with a few versions of Ruby-interpreters some time ago.
How I can to update it, because new versions are already released?

I found only one way: `rvm install 1.9.2-rc1 &amp;&amp; rvm remove 1.9.2-preview1`, but my gems are lost.
Can I update branches time to time? I haven&#39;t found any tips in the documentation.

How do I update Ruby-interpreters with RVM?

I&#39;m wondering what&#39;s the best, the cleanest and the most simply way to work with many-to-many relations in Doctrine2. 

Let&#39;s assume that we&#39;ve got an album like [*Master of Puppets* by Metallica](http://www.last.fm/music/Metallica/Master+of+Puppets) with several tracks. But please note the fact that one track might appears in more that one album, like [*Battery* by Metallica](http://www.last.fm/music/Metallica/Master+of+Puppets/Battery) does - three albums are featuring this track.

So what I need is many-to-many relationship between albums and tracks, using third table with some additional columns (like position of the track in specified album). Actually I have to use, as Doctrine&#39;s documentation suggests, a double one-to-many relation to achieve that functionality.

    /** @Entity() */
    class Album {
    	/** @Id @Column(type=&quot;integer&quot;) */
    	protected $id;
    	
    	/** @Column() */
    	protected $title;
    	
    	/** @OneToMany(targetEntity=&quot;AlbumTrackReference&quot;, mappedBy=&quot;album&quot;) */
    	protected $tracklist;
    	
    	public function __construct() {
    		$this-&gt;tracklist = new \Doctrine\Common\Collections\ArrayCollection();
    	}
    	
    	public function getTitle() {
    		return $this-&gt;title;
    	}
    	
    	public function getTracklist() {
    		return $this-&gt;tracklist-&gt;toArray();
    	}
    }
    
    /** @Entity() */
    class Track {
    	/** @Id @Column(type=&quot;integer&quot;) */
    	protected $id;
    	
    	/** @Column() */
    	protected $title;
    	
    	/** @Column(type=&quot;time&quot;) */
    	protected $duration;
    	
    	/** @OneToMany(targetEntity=&quot;AlbumTrackReference&quot;, mappedBy=&quot;track&quot;) */
    	protected $albumsFeaturingThisTrack; // btw: any idea how to name this relation? :)
    	
    	public function getTitle() {
    		return $this-&gt;title;
    	}
    	
    	public function getDuration() {
    		return $this-&gt;duration;
    	}
    }
    
    /** @Entity() */
    class AlbumTrackReference {
    	/** @Id @Column(type=&quot;integer&quot;) */
    	protected $id;
    	
    	/** @ManyToOne(targetEntity=&quot;Album&quot;, inversedBy=&quot;tracklist&quot;) */
    	protected $album;
    	
    	/** @ManyToOne(targetEntity=&quot;Track&quot;, inversedBy=&quot;albumsFeaturingThisTrack&quot;) */
    	protected $track;
    	
    	/** @Column(type=&quot;integer&quot;) */
    	protected $position;
    	
    	/** @Column(type=&quot;boolean&quot;) */
    	protected $isPromoted;
    	
    	public function getPosition() {
    		return $this-&gt;position;
    	}
    	
    	public function isPromoted() {
    		return $this-&gt;isPromoted;
    	}
    	
    	public function getAlbum() {
    		return $this-&gt;album;
    	}
    	
    	public function getTrack() {
    		return $this-&gt;track;
    	}
    }

Sample data:

                 Album
    +----+--------------------------+
    | id | title                    |
    +----+--------------------------+
    |  1 | Master of Puppets        |
    |  2 | The Metallica Collection |
    +----+--------------------------+
    
                   Track
    +----+----------------------+----------+
    | id | title                | duration |
    +----+----------------------+----------+
    |  1 | Battery              | 00:05:13 |
    |  2 | Nothing Else Matters | 00:06:29 |
    |  3 | Damage Inc.          | 00:05:33 |
    +----+----------------------+----------+
    
                  AlbumTrackReference
    +----+----------+----------+----------+------------+
    | id | album_id | track_id | position | isPromoted |
    +----+----------+----------+----------+------------+
    |  1 |        1 |        2 |        2 |          1 |
    |  2 |        1 |        3 |        1 |          0 |
    |  3 |        1 |        1 |        3 |          0 |
    |  4 |        2 |        2 |        1 |          0 |
    +----+----------+----------+----------+------------+

Now I can display a list of albums and tracks associated to them:

    $dql = &#39;
    	SELECT   a, tl, t
    	FROM     Entity\Album a
    	JOIN     a.tracklist tl
    	JOIN     tl.track t
    	ORDER BY tl.position ASC
    &#39;;
    
    $albums = $em-&gt;createQuery($dql)-&gt;getResult();
    
    foreach ($albums as $album) {
    	echo $album-&gt;getTitle() . PHP_EOL;
    	
    	foreach ($album-&gt;getTracklist() as $track) {
    		echo sprintf(&quot;\t#%d - %-20s (%s) %s\n&quot;, 
    			$track-&gt;getPosition(),
    			$track-&gt;getTrack()-&gt;getTitle(),
    			$track-&gt;getTrack()-&gt;getDuration()-&gt;format(&#39;H:i:s&#39;),
    			$track-&gt;isPromoted() ? &#39; - PROMOTED!&#39; : &#39;&#39;
    		);
    	}	
    }

The results are what I&#39;m expecting, ie: a list of albums with their tracks in appropriate order and promoted ones being marked as promoted.

    The Metallica Collection
    	#1 - Nothing Else Matters (00:06:29) 
    Master of Puppets
    	#1 - Damage Inc.          (00:05:33) 
    	#2 - Nothing Else Matters (00:06:29)  - PROMOTED!
    	#3 - Battery              (00:05:13) 

## So what&#39;s wrong?

This code demonstrates what&#39;s wrong:

    foreach ($album-&gt;getTracklist() as $track) {
        echo $track-&gt;getTrack()-&gt;getTitle();
    }

`Album::getTracklist()` returns an array of `AlbumTrackReference` objects instead of `Track` objects. I can&#39;t create proxy methods cause what if both, `Album` and `Track` would have `getTitle()` method? I could do some extra processing within `Album::getTracklist()` method but what&#39;s the most simply way to do that? Am I forced do write something like that?

    public function getTracklist() {
        $tracklist = array();
    
        foreach ($this-&gt;tracklist as $key =&gt; $trackReference) {
            $tracklist[$key] = $trackReference-&gt;getTrack();
     
            $tracklist[$key]-&gt;setPosition($trackReference-&gt;getPosition());
            $tracklist[$key]-&gt;setPromoted($trackReference-&gt;isPromoted());
        }
    
        return $tracklist;
    }
    
    // And some extra getters/setters in Track class

#EDIT

@beberlei suggested to use proxy methods:

    class AlbumTrackReference {
        public function getTitle() {
            return $this-&gt;getTrack()-&gt;getTitle()
        }
    }

That would be a good idea but I&#39;m using that &quot;reference object&quot; from both sides: `$album-&gt;getTracklist()[12]-&gt;getTitle()` and `$track-&gt;getAlbums()[1]-&gt;getTitle()`, so `getTitle()` method should return different data based on the context of invocation.

I would have to do something like:

     getTracklist() {
         foreach ($this-&gt;tracklist as $trackRef) { $trackRef-&gt;setContext($this); }
     }

     // ....
   
     getAlbums() {
         foreach ($this-&gt;tracklist as $trackRef) { $trackRef-&gt;setContext($this); }
     }

     // ...

     AlbumTrackRef::getTitle() {
          return $this-&gt;{$this-&gt;context}-&gt;getTitle();
     }

And that&#39;s not a very clean way.

Doctrine2: Best way to handle many-to-many with extra columns in reference table

What is the difference between a MVC Model object, a domain object and a DTO?

My understanding is:

**MVC Model object:**

Models the data to be displayed by a corresponding view. It may not map directly to a domain object, i.e. may include data from one or more domain objects.

 1. Client side
 2. May contain business logic. Eg. validations, calculated properties, etc
 3. No persistence related methods

**Domain object:**

An object that models real-world object in the problem domain like Reservation, Customer, Order, etc. Used to persist data.

 1. Server side
 2. No business logic


**DTO (Data Transfer Object):**

An object used to transfer data between layers when the layers are in separate processes, e.g. from a DB to a client app. Allows a single transaction across the wire rather than multiple calls when fetching data corresponding to multiple domain objects. A DTO contains just data and accessor methods and there is no logic present. The data is for a particular DB transaction, so it may or may not directly map to a domain object as it may include data from one or more domain objects.

 1. Used on both server and client sides as it is passed between layers
 2. No business logic
 3. No persistence related methods

So, the questions:

 1. Is above understanding correct? Am I missing some key points?

 2. Are there any reasons not to use Domain objects as the MVC Model assuming that the Model objects do not require extra business logic?

 3. Are there any reasons not to use DTOs as the MVC Model assuming that the Model objects do not require extra business logic?


What is the difference between an MVC Model object, a domain object and a DTO

I&#39;m setting up an after_save callback in my model observer to send a notification only if the model&#39;s *published* attribute was changed from false to true. Since methods such as *changed?* are only useful before the model is saved, the way I&#39;m currently (and unsuccessfully) trying to do so is as follows:

    def before_save(blog)
      @og_published = blog.published?
    end
    
    def after_save(blog)
      if @og_published == false and blog.published? == true
        Notification.send(...)
      end
    end

Does anyone have any suggestions as to the best way to handle this, preferably using model observer callbacks (so as not to pollute my controller code)?

Determine what attributes were changed in Rails after_save callback?

I have looked through the Ruby on Rails guides and I can&#39;t seem to figure out how to prevent someone from deleting a Parent record if it has Children.  For example.  If my database has **CUSTOMERS** and each customer can have multiple **ORDERS**, I want to prevent someone from deleting a customer if it has any orders in the database.  They should only be able to delete a customer if it has no orders.

Is there a way when defining the association between models to enforce this behavior?

How do I prevent deletion of parent if it has child records?

OK, I have been hearing discussion about &quot;ViewModels&quot; in regards to MS&#39;s ASP.NET MVC.

Now, that is intended to be a specific kind of Model, correct?  Not a specific kind of View.

To my understanding, it&#39;s a kind of Model that has a specific purpose of interacting with the View?  Or something like that?

Some clarification would be appreciated.

Content Type	Original Author	Original Content on Stackoverflow
Question	Croplio	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Faisal	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	John Topley	View Answer on Stackoverflow
Solution 3 - Ruby on-Rails	Thorin	View Answer on Stackoverflow

How to know whether a model is new or not?

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

Solution 3 - Ruby on-Rails

Is "git push --mirror" sufficient for backing up my repository?

Convenient way to parse incoming multipart/form-data parameters in a Servlet

Attributions