Rails has 2 ways of avoiding the n+1 problem. One involves creating a big join based query to pull in your associations, the other involves making a separate query per association.

When you do `includes` rails decides which strategy to use for you. It defaults to the separate query approach (preloading) unless it thinks you are using the columns from the associations in you conditions or order. Since that only works with the joins approach it uses that instead. 

 Rails&#39; heuristics sometimes get it wrong or you may have a specific reason for preferring one approach over the other. `preload` ( and its companion method `eager_load`) allow you to specify which strategy you want rails to use.

As apidoc said &quot;This method is deprecated or moved on the latest stable version. The last existing version (v3.0.9) is shown here.&quot; So the difference is that includes just NOT deprecated.

How can you explain very well, to a **beginner**, the meaning of `String args[]` and the use of `static` in the following excerpt?

    class FirstApp {
        public static void main(String[] args) {
            ...
        }
    }

Explanation of &#39;String args[]&#39; and static in &#39;public static void main(String[] args)&#39;

I need current path from url in template (content of $location.path). But not via controller, because I have a lot of controllers (and I do not want to duplicate declaration of `$scope.currentUrl = $location.path;`). Thanks for the advice.

AngularJS: how can I get $location.path to template

I&#39;m struggling to find a comparison of includes() and preload() for ActiveRecord objects. Can anyone explain the difference ?

What&#39;s the difference between “includes” and “preload” in an ActiveRecord query?

<p>I'm struggling to find a comparison of includes() and preload() for ActiveRecord objects. Can anyone explain the difference ?</p>


For some inexplicable reason, RubyMine autosaves every change you make and so every key stroke will trigger Guard to run your tests!  And the most ridiculous thing is that there&#39;s apparently no way to disable this autosaving &quot;feature&quot;.  I&#39;m just wondering, RubyMine seems to be a very popular editor among Rails developers and Guard seems to be an indispensable tool used to automate testing.  Since Guard is impossible to use reasonably with RubyMine, how do people deal with automating their tests with RubyMine? 

Is it impossible to use Guard with RubyMine?

Is it possible to somehow run `Rails.cache.clear` and only clear keys with a certain name/string?

I don&#39;t want to clear the entire cache...just keys with the string `blog/post` in the name (ie. `blog/post/1`, `blog/post/2`).

I&#39;m using [dalli][1] with memcached for my cache and running Rails 3.0.6.


  [1]: https://github.com/mperham/dalli

Rails.cache.clear certain key names?

According to Rails doc: http://guides.rubyonrails.org/migrations.html

&quot;Active Record tracks which migrations have already been run so all you have to do is update your source and run rake db:migrate.&quot;

How does ActiveRecord actually do this?  Where does Active Record store the data?

I suspect this might be stored in the database itself?  In a table somewhere.

On my development machine, I ran all the migrations.  Then I copied the production database over using mysqldump.  Then I ran &quot;rake db:migrate:status&quot;, it shows correctly the migrations that need to run on the production database.

I used to think that ActiveRecord keeps track of the last migration run using the timestamp.  But I think this is not true because ActiveRecord correctly runs the &quot;older&quot; migrations merged in from another code branch.

Could someone with inside knowledge of this elaborate?
Thanks

How does Rails keep track of which migrations have run for a database?

I am in an older Rails project that has a Gemfile. I tried to add a gem to the Gemfile and `bundle install` but got an error:

    Bundler could not find compatible versions for gem &quot;bundler&quot;:
      In Gemfile:
        rails (= 3.0.0) ruby depends on
          bundler (~&gt; 1.0.0) ruby
    
      Current Bundler version:
        bundler (1.1.5)
    
    This Gemfile requires a different version of Bundler.

The version of Rails it&#39;s using requires bundler ~&gt;1.0.0 but I have 1.1.5 installed and am using it for my other projects. Usually I would use `bundle exec ...` but since this is bundler we are talking about, it&#39;s a little more complicated than that. How can I add a gem to my Gemfile and run `bundle install` while using the version of bundler that it requires?


How to `bundle install` when your Gemfile requires an older version of bundler?

I have this code: 

    &lt;%= link_to image_tag(&quot;facebook.png&quot;, :class =&gt; &quot;facebook_icon&quot;, :alt =&gt; &quot;Facebook&quot;, :target =&gt; &quot;_blank&quot;),                 
                &quot;http://www.facebook.com/mypage&quot; %&gt;

How can I make it open in a new tab when a user clicks the link?

Rails: Open link in new tab (with &#39;link_to&#39;)

How can I convert a hash into a struct in ruby?

Given this:

    h = { :a =&gt; 1, :b =&gt; 2 }

I want a struct such that:

    s.a == 1
    s.b == 2

Convert a hash into a struct

I&#39;m new to programming. Can someone explain what `.map` would do in:

    params = (0...param_count).map



What does the &quot;map&quot; method do in Ruby?

I&#39;m new to programming. Right now I&#39;m studying Ruby. To my understanding, global variables are defined in the global namespace (so outside of any classes or functions). I&#39;m reading something and it says global variables have a `$` sign before them. What does that mean? Does it mean when I define a function or class and want to reference my global variable (let&#39;s say it is `edmund = 123`) I would have to reference it like this: `$edmund`?

so:

    edmund = 123
    def my_function()
      456 + $edmund
    end


Also are class variables (the ones that begin with `@@`) like instance variables (`@`) where you can access them by calling them through `Class.classvariable`? What is their purpose?

How to reference global variables and class variables?

If an instance variable belongs to a class, can I access the instance variable (e.g. `@hello`) directly using the class instance?

    class Hello
      def method1
        @hello = &quot;pavan&quot;
      end
    end
    
    h = Hello.new
    puts h.method1



Access instance variable from outside the class

Rails 3.2.1

Is there a way (without [squeel][1]) to use the hash syntax of ActiveRecord to construct a `!=` operator?

Something like `Product.where(id: !params[:id])`

Generates `SELECT products.* FROM products WHERE id != 5`

Looking for the opposite of `Product.where(id: params[:id])`

**UPDATE**

In rails 4 there is a `not` operator.

`Product.where.not(id: params[:id])`


  [1]: https://github.com/activerecord-hackery/squeel

Rails ActiveRecord Query for Not Equal

How do you write in the Rails way?
I have a model - Managers.
I want to delete all records from Managers that meet the condition that manager_level is 5.

Thank you.

Rails - Delete all Records that Meet a Condition

Here is my query using fluent query builder.

 

		$query = DB::table(&#39;category_issue&#39;)
		    -&gt;select(&#39;issues.*&#39;)
			-&gt;where(&#39;category_id&#39;, &#39;=&#39;, 1)
			-&gt;join(&#39;issues&#39;, &#39;category_issue.issue_id&#39;, &#39;=&#39;, &#39;issues.id&#39;)
			-&gt;left_join(&#39;issue_subscriptions&#39;, &#39;issues.id&#39;, &#39;=&#39;, &#39;issue_subscriptions.issue_id&#39;)
			-&gt;group_by(&#39;issues.id&#39;)
			-&gt;order_by(DB::raw(&#39;COUNT(issue_subscriptions.issue_id)&#39;), &#39;desc&#39;)
			-&gt;get();

As you can see, I am ordering by a count from the joined table. This is working fine. However, I want this count returned with my selections. 

Here is the my raw sequel query that works fine.

 

  

    Select issues.*, COUNT(issue_subscriptions.issue_id) AS followers 
    FROM category_issue JOIN Issues ON category_issue.issue_id = issues.id 
    LEFT JOIN issue_subscriptions ON issues.id = issue_subscriptions.issue_id
    WHERE category_issue.category_id = 1
    GROUP BY issues.id
    ORDER BY followers DESC

How would I go about this select using Laravel&#39;s fluent query builder? I am aware I can use a raw sql query but I would like to avoid that if possible. Any help would be appreciated, thanks in advance!



How to select count with Laravel&#39;s fluent query builder?

I want to make a `migration` in Rails, referencing another table. Usually, I would do something like:

    add_column :post, :user, :references

This creates a column named `user_id` in `posts` table. But what if, instead of `user_id`, I want something like `author_id`? How can I do that?

Content Type	Original Author	Original Content on Stackoverflow
Question	Phantomwhale	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Frederick Cheung	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	freeze	View Answer on Stackoverflow

What's the difference between “includes” and “preload” in an ActiveRecord query?

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

AngularJS: how can I get $location.path to template

Explanation of 'String args[]' and static in 'public static void main(String[] args)'

Attributions