The easiest way to do this is to just add an order clause to the original query. If you give the count method a specific field, it will generate an output column with the name count_{column}, which can be used in the sql generated by adding an order call:

    Message.where(&#39;message_type = ?&#39;,&#39;incoming&#39;)
           .group(&#39;sender_number&#39;)
           .order(&#39;count_id asc&#39;).count(&#39;id&#39;)

When I tried this, rails gave me this error

    SQLite3::SQLException: no such column: count_id: SELECT  COUNT(*) AS count_all, state AS state FROM &quot;ideas&quot;  GROUP BY state ORDER BY count_id desc LIMIT 3

Notice that it says SELECT ... AS count_all

So I updated the query from @Simon&#39;s answer to look like this and it works for me

    .order(&#39;count_all desc&#39;)

Please take a look at the following simple code:

    class Foo
    {
    public:
      Foo(){}
      ~Foo(){}
    
      Foo(const Foo&amp;){}
      Foo&amp; operator=(const Foo&amp;) { return *this; }
    };
    
    static Foo g_temp;
    const Foo&amp; GetFoo() { return g_temp; }

I tried to use `auto` like this:

    auto my_foo = GetFoo();

I expected that `my_foo` will be a constant reference to `Foo`, which is the return type of the function. However, the type of `auto` is `Foo`, not the reference. Furthermore, `my_foo` is created by copying `g_temp`. This behavior isn&#39;t that obvious to me.

In order to get the reference to `Foo`, I needed to write like this:

    const auto&amp; my_foo2 = GetFoo();
          auto&amp; my_foo3 = GetFoo();



**Question**: Why does `auto` deduce the return type of `GetFoo` as an object, not a reference?

C++11 auto: what if it gets a constant reference?

I am using [Flot][1] to graph some of my data and I was thinking it would be great to make this graph appear fullscreen (occupy full space on the monitor) upon clicking on a button. Currently, my `div` is as follows:

    &lt;div id=&quot;placeholder&quot; style=&quot;width:800px;height:600px&quot;&gt;&lt;/div&gt;

Of course, the style attribute is only for testing. I will move this to `CSS` after during the actual design. Is there anyway I could make this div fullscreen and still preserve all event handling?


  [1]: http://people.iola.dk/olau/flot/examples/

How do I make a div full screen?

This query 

    Message.where(&quot;message_type = ?&quot;, &quot;incoming&quot;).group(&quot;sender_number&quot;).count
     
will return me an hash.

    OrderedHash {&quot;1234&quot;=&gt;21, &quot;2345&quot;=&gt;11, &quot;3456&quot;=&gt;63, &quot;4568&quot;=&gt;100}

Now I want to order by count of each group. How can I do that within the query.



&quot;Order by&quot;  result of  &quot;group by&quot; count?

This query
<pre><code class="hljs language-csharp">Message.where("message_type = ?", "incoming").group("sender_number").count
 
</code></pre>
will return me an hash.
<pre><code class="hljs language-ini">OrderedHash {"1234"=>21, "2345"=>11, "3456"=>63, "4568"=>100}
</code></pre>
Now I want to order by count of each group. How can I do that within the query.

I want to use a column called `type` without invoking Single Table Inheritance (STI) - I just want `type` to be a normal column that holds a `String`.

How can I do this without having Rails expecting me to have single table inheritance and throwing an exception of `The single-table inheritance mechanism failed to locate the subclass...This error is raised because the column &#39;type&#39; is reserved for storing the class in case of inheritance.`?

Any ideas on how to do this?

Rails -- use type column without STI?

Ran into this error message whilst developing tonight: `SQLite3::BusyException: database is locked:`

I have two models: 

- Podcasts have many Tracks 
- Tracks belong to Podcasts.
- Podcast files are hosted on [mixcloud](http://www.mixcloud.com).

To create a Podcast:

- user submits a url for a podcast on mixcloud
- rails app grabs json feed associated with url
- json is used to set attributes (title, image etc) on the new Podcast object

I&#39;m trying to get my rails app to take advantage of the fact that the json feed also details the names (and artists) of the Tracks that belong to this Podcast.

I thought the following before_validation method would automatically create all associated Tracks whenever we create a new Podcast.

    class Podcast &lt; ActiveRecord::Base
      attr_accessible :mixcloud_url, :lots, :of, :other, :attrs
      has_many :tracks    
      before_validation :create_tracks
      def create_tracks
        json = Hashie::Mash.new HTTParty.get(self.json_url)    
        json.sections.each do |section|
          if section.section_type==&quot;track&quot;
              Track.create(:name=&gt;section.track.name, :podcast_id=&gt;self.id)
          end
        end             
      end
    end

How can I get round this? It looks like rails (or sqlite3) doesn&#39;t like me creating new instances of an associated model in this way. How else can I do this? I suspect this is as much a rails problem as an sqlite3 one. I can post more code if it&#39;s gonna help.


Ruby: SQLite3::BusyException: database is locked:

This might be a dumb question but when I&#39;m putting together an HTML email in Rails, is there a particularly easy built-in way to preview the template it in the browser or do I need to write some sort of custom controller that pulls it in as its view?

How do I preview emails in Rails?

I was wondering how I would best validate URLs in Rails. I was thinking of using a regular expression, but am not sure if this is the best practice.

And, if I were to use a regex, could someone suggest one to me? I am still new to Regex.

Rails: What&#39;s a good way to validate links (URLs)?

Is there an easy way (i.e. a configuration) to force ActiveRecord to save empty strings as NULL in the DB (if the column allows)? 

The reason for this is that if you have a NULLable string column in the DB without a default value, new records that do not set this value will contain NULL, whereas new records that set this value to the empty string will not be NULL, leading to inconsistencies in the database that I&#39;d like to avoid.

Right now I&#39;m doing stuff like this in my models:

    before_save :set_nil

    def set_nil
      [:foo, :bar].each do |att|
        self[att] = nil if self[att].blank?
      end
    end

which works but isn&#39;t very efficient or DRY. I could factor this out into a method and mix it into ActiveRecord, but before I go down that route, I&#39;d like to know if there&#39;s a way to do this already.

Rails: Force empty string to NULL in the database

I have a User model that belongs to a Group. Group must have unique name attribute. User factory and group factory are defined as:

    Factory.define :user do |f|
      f.association :group, :factory =&gt; :group
      # ...
    end

    Factory.define :group do |f|
      f.name &quot;default&quot;
    end

When the first user is created a new group is created too. When I try to create a second user it fails because it wants to create same group again.

Is there a way to tell factory_girl association method to look first for an existing record?

Note: I did try to define a method to handle this, but then I cannot use f.association. I would like to be able to use it in Cucumber scenarios like this:

    Given the following user exists:
      | Email          | Group         |
      | test@email.com | Name: mygroup |

and this can only work if association is used in Factory definition.

Find or create record through factory_girl association

Is there a more correct way to output the contents of an array as a comma delimited string

    @emails = [&quot;joe@example.com&quot;, &quot;Peter@example.com&quot;, &quot;alice@example.com&quot;]
    
    @emails * &quot;,&quot;
    
    =&gt; &quot;joe@example.com&quot;, &quot;Peter@example.com&quot;, &quot;alice@example.com&quot;

This works but I am sure there must be a more elegant solution.

Ruby output contents of an array as a comma separated string Ruby

I have an observer and I register an `after_commit` callback.
How can I tell  whether it was fired after create or update?
I can tell an item was destroyed by asking `item.destroyed?` but `#new_record?` doesn&#39;t work since the item was saved.

I was going to solve it by adding `after_create`/`after_update` and do something like `@action = :create` inside and check the `@action` at `after_commit`, but it seems that the observer instance is a singleton and I might just override a value before it gets to the `after_commit`. So I solved it in an uglier way, storing the action in a map based on the item.id on after_create/update and checking its value on after_commit. Really ugly.

Is there any other way?

# Update

As @tardate said, `transaction_include_action?` is a good indication, though it&#39;s a private method, and in an observer it should be accessed with `#send`.

    class ProductScoreObserver &lt; ActiveRecord::Observer
      observe :product

      def after_commit(product)
        if product.send(:transaction_include_action?, :destroy)
          ...

Unfortunately, the `:on` option does not work in observers.

Just make sure you test the hell of your observers (look for `test_after_commit` gem if you use use_transactional_fixtures) so when you upgrade to new Rails version you&#39;ll know if it still works.

(Tested on 3.2.9)

# Update 2

Instead of Observers I now use ActiveSupport::Concern and `after_commit :blah, on: :create` works there.

Rails 3: How to identify after_commit action in observers? (create/update/destroy)

Getting the following error when running rspec tests

&gt;&gt; unable to obtain stable firefox connection in 60 seconds (127.0.0.1:7055) in rails

Using latest ruby (1.9.2) and firefox (6.0)

Using rspec-rails, capybara and several other gems, but they don&#39;t seem to be a problem. These tests run fine in another environment (linux).

unable to obtain stable firefox connection in 60 seconds (127.0.0.1:7055)

    class Agents &lt;&lt; ActiveRecord::Base
      belongs_to :customer
      belongs_to :house
    end

    class Customer &lt;&lt; ActiveRecord::Base
      has_many :agents
      has_many :houses, through: :agents
    end
    
    class House &lt;&lt; ActiveRecord::Base
      has_many :agents
      has_many :customers, through: :agents
    end


How do I add to the `Agents` model for `Customer`?

Is this the best way?

    Customer.find(1).agents.create(customer_id: 1, house_id: 1)

The above works fine from the console however, I don&#39;t know how to achieve this in the actual application. 

Imagine a form is filled for the customer that also takes `house_id` as input. Then do I do the following in my controller?

    def create 
      @customer = Customer.new(params[:customer])
      @customer.agents.create(customer_id: @customer.id, house_id: params[:house_id])
      @customer.save
    end

Overall I&#39;m confused as to how to add records in the `has_many :through` table?





how to add records to has_many :through association in rails

I have a particularly complex model with validations and callbacks defined. The business needs now calls for a particular scenario where adding a new record requires skipping the validations and callbacks. What&#39;s the best way to do this?

Rails 3 skip validations and callbacks

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

Determine if ActiveRecord Object is New

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

**Short Question**  
What is the default order of a list returned from a Django filter call when connected to a PostgreSQL database?  

**Background**  
By my own admission, I *had* made a poor assumption at the application layer in that the order in which a list is returned will be constant, that is without using &#39;order_by&#39;.  The list of items I was querying is not in alphabetic order or any other **deliberate** order.  It was thought to remain in the same order as which they were added to the database.  

This assumption held true for hundreds of queries, but a failure was reported by my application when the order changed unknowingly.  To my knowledge, none of these records were touched during this time as I am the only person who maintains the DB.  To add to the confusion, when running the Django app on Mac OS X, it still worked as expected, but on Win XP, it changed the order.  (Note that the mentioned hundreds of queries was on Win XP).  

Any insight to this would be helpful as I could not find anything in the Django or PostgreSQL documentation that explained the differences in operating systems. 

**Example Call**  

    required_tests = Card_Test.objects.using(get_database()).filter(name__icontains=key)


**EDIT**  
After speaking with some colleague&#39;s of mine today, I had come up with the same answer as Bj&#246;rn Lindqvist.  

Looking back, I definitely understand why this is done wrong so often.  One of the benefits to using an ORM Django, sqlalchemy, or whatever is that you can write commands without having to know or understand (in detail) the database it&#39;s connected to.  Admittedly I happen to have been one of these users.  However on the flip-side of this is that without knowing the database in detail debugging errors like this are quite troublesome and potentially catastrophic.  

What is the default order of a list returned from a Django filter call?

Is there a way with PostgreSQL to sort rows with `NULL` values in fields to the end of the selected table?

Like:

    SELECT * FROM table ORDER BY somevalue, PUT_NULL_TO_END

Sort NULL values to the end of a table

I want to sort the following data items in the order they are presented below (numbers 1-12):
&lt;pre&gt;
1
2
3
4
5
6
7
8
9
10
11
12&lt;/pre&gt;


However, my query - using `order by xxxxx asc` sorts by the first digit above all else:
&lt;pre&gt;
1
10
11
12
2
3
4
5
6
7
8
9&lt;/pre&gt;

Any tricks to make it sort more properly?

Further, in the interest of full disclosure, this could be a mix of letters and numbers (although right now it is not), e.g.:
&lt;pre&gt;
A1
534G
G46A
100B
100A
100JE
&lt;/pre&gt;
etc....

Thanks!

**update: people asking for query**

    select * from table order by name asc

MySQL &#39;Order By&#39; - sorting alphanumeric correctly

I&#39;ve [a table][1] like:

    +-----------+-------+------------+
    | client_id | views | percentage |
    +-----------+-------+------------+
    |         1 |     6 |         20 |
    |         1 |     4 |         55 |
    |         1 |     9 |         56 |
    |         1 |     2 |         67 |
    |         1 |     7 |         80 |
    |         1 |     5 |         66 |
    |         1 |     3 |         33 |
    |         1 |     8 |         34 |
    |         1 |     1 |         52 |







I tried `group_concat`:

    SELECT li.client_id, group_concat(li.views) AS views,  
    group_concat(li.percentage) FROM li GROUP BY client_id;

    +-----------+-------------------+-----------------------------+
    | client_id | views             | group_concat(li.percentage) |
    +-----------+-------------------+-----------------------------+
    |         1 | 6,4,9,2,7,5,3,8,1 | 20,55,56,67,80,66,33,34,52  |
    +-----------+-------------------+-----------------------------+

But I want to get the views in order, like:

    +-----------+-------------------+----------------------------+
    | client_id | views             | percentage                 |
    +-----------+-------------------+----------------------------+
    |         1 | 1,2,3,4,5,6,7,8,9 | 52,67,33,55,66,20,80,34,56 |
    +-----------+-------------------+----------------------------+


  [1]: http://googledrive.com/host/0B53jM4a9X2fqfkhfeV83Tm05VnU4cV9ZSWZlMUNTQzRZUUJQTFdQZUptOEJkdXkyVXFIYmM

GROUP_CONCAT ORDER BY

What is the most efficient method of showing my data in descending order?


    public String getRank() {

		String[] rank = new String[]{ KEY_ROWID };
		Cursor c = scoreDb.query(DATABASE_TABLE, rank, null, null, null, null, null);	//reading information from db.
		String rankResult = &quot;&quot;;

		int iRow = c.getColumnIndex(KEY_ROWID); //Cursor looking for column setting equal to these ints.
		

		for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) { 
			//Move to first row - where cursor starts and moves to next row as long it is not after last row.
			rankResult = rankResult + c.getString(iRow) + &quot;\n&quot;; 
			//Returning value of row that it is currently on.
		}
		return rankResult;	//returning result
	}
	
	public String getName() {

		String[] name = new String[]{ KEY_NAME };
		Cursor c = scoreDb.query(DATABASE_TABLE, name, null, null, null, null, null);	//reading information from db.
		String nameResult = &quot;&quot;;

		int iRow1 = c.getColumnIndex(KEY_NAME); //Cursor looking for column setting equal to these ints.
		

		for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) { 
			//Move to first row - where cursor starts and moves to next row as long it is not after last row.
			nameResult = nameResult + c.getString(iRow1) + &quot;\n&quot;; 
			//Returning value of row that it is currently on.
		}
		return nameResult;	//returning result
	}
	
	public String getScore() {

		String[] score = new String[]{ KEY_SCORE };
		Cursor c = scoreDb.query(DATABASE_TABLE, score, null, null, null,null, null);	//reading information from db.
		String scoreResult = &quot;&quot;;
		
		int iRow2 = c.getColumnIndex(KEY_SCORE); //Cursor looking for column setting equal to these ints.
		

		for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) { 
			//Move to first row - where cursor starts and moves to next row as long it is not after last row.
			scoreResult = scoreResult + c.getString(iRow2) + &quot;\n&quot;; 
			//Returning value of row that it is currently on.
		}
		return scoreResult;	//returning result
	}

Content Type	Original Author	Original Content on Stackoverflow
Question	Mohit Jain	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Simon Elliston Ball	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	penner	View Answer on Stackoverflow

"Order by" result of "group by" count?

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

How do I make a div full screen?

C++11 auto: what if it gets a constant reference?

Attributions