You can pass a `include_blank: false, include_hidden: false` option:

    = f.input :category, :as =&gt; :select, :label =&gt; false, :collection =&gt; Choices[&quot;Categories&quot;], include_blank: false, include_hidden: false

or you can customize call back action in your model to remove any empty string in the array parameter, assuming a parameter with the name &quot;types&quot;:

    before_validation :remove_empty_string

    def remove_empty_string
      types.reject! { |l| l.empty? }
    end

To remove a blank field from select it is necessary to show the selected so add `selected: 1`
Then set prompt to anything like `prompt: &quot;Please Select&quot;`
The final output will be 
`&lt;%= select(&quot;social_links&quot;,:option_id, Option.all.collect {|p| [ p.name, p.id ] },{ selected: 1 , prompt: &quot;Please Select&quot;}, { class: &#39;form-control&#39; , required:true})%&gt;
  `

Here is an exercise from Introductory Statistics with R:

With the rmr data set, plot metabolic rate versus body weight. Fit a linear regression model to the relation. According to the fitted model, what is the predicted metabolic rate for a body weight of 70 kg? Give a 95% confidence interval for the slope of the line.

rmr data set is in the &#39;ISwR&#39; package. It looks like this:

    &gt; rmr
       body.weight metabolic.rate
    1         49.9           1079
    2         50.8           1146
    3         51.8           1115
    4         52.6           1161
    5         57.6           1325
    6         61.4           1351
    7         62.3           1402
    8         64.9           1365
    9         43.1            870
    10        48.1           1372
    11        52.2           1132
    12        53.5           1172
    13        55.0           1034
    14        55.0           1155
    15        56.0           1392
    16        57.8           1090
    17        59.0            982
    18        59.0           1178
    19        59.2           1342
    20        59.5           1027
    21        60.0           1316
    22        62.1           1574
    23        64.9           1526
    24        66.0           1268
    25        66.4           1205
    26        72.8           1382
    27        74.8           1273
    28        77.1           1439
    29        82.0           1536
    30        82.0           1151
    31        83.4           1248
    32        86.2           1466
    33        88.6           1323
    34        89.3           1300
    35        91.6           1519
    36        99.8           1639
    37       103.0           1382
    38       104.5           1414
    39       107.7           1473
    40       110.2           2074
    41       122.0           1777
    42       123.1           1640
    43       125.2           1630
    44       143.3           1708

I know how to calculate the predicted y at a given x but how can I calculate the confidence interval for the slope?

How to calculate the 95% confidence interval for the slope in a linear regression model in R

When return value is not of interest, is there any (even irrelevant in practice) difference between [`AtomicInteger.getAndIncrement()`][1] and [`AtomicInteger.incrementAndGet()`][2] methods, when return value is ignored?

I&#39;m thinking of differences like which would be more idiomatic, as well as which would put less load in CPU caches getting synchronized, or anything else really, anything to help decide which one to use more rationally than tossing a coin.

  [1]: http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/atomic/AtomicInteger.html#getAndIncrement%28%29
  [2]: http://docs.oracle.com/javase/1.5.0/docs/api/java/util/concurrent/atomic/AtomicInteger.html#incrementAndGet%28%29

AtomicInteger.incrementAndGet() vs. AtomicInteger.getAndIncrement()

I have this piece of code:

    = f.input :category, :as =&gt; :select, :label =&gt; false, :collection =&gt; Choices[&quot;Categories&quot;]

Choices[&quot;Categories&quot;] is just a hash of key=&gt;value pairs.

SimpleForm generates a select field with all needed options, but it also makes the first option blank.&lt;br/&gt; This blank option is present in all select fields that were generated by SimpleForm.

But I don&#39;t want to have a blank option. Is there a way to get rid of it?

Something like `:allow_blank_option =&gt; false`?

I tried to make a presence validation of this attribute hoping that SimpleForm will detect it, but it didn&#39;t help.

remove a blank option of select field that was generated by SimpleForm

I have this piece of code:
<pre><code class="hljs language-ruby">= f.input :category, :as => :select, :label => false, :collection => Choices["Categories"]
</code></pre>
Choices["Categories"] is just a hash of key=>value pairs.
SimpleForm generates a select field with all needed options, but it also makes the first option blank. This blank option is present in all select fields that were generated by SimpleForm.
But I don't want to have a blank option. Is there a way to get rid of it?
Something like <code>:allow_blank_option => false</code>?
I tried to make a presence validation of this attribute hoping that SimpleForm will detect it, but it didn't help.

I can&#39;t get capybara working with rspec. It gives me this error:

    undefined method `visit&#39; for #&lt;RSpec::Core::ExampleGroup::Nested_1:0x16529f8 @example=nil&gt;

I know there are lots of posts about this but non of the solutions are working for me. Most of them involve the specs not being in /spec/features - which mine is in.

First the error:
&lt;!-- language-all: lang-rb --&gt;

    $bundle exec rspec spec
    F

    Failures:

      1) security signs users in
         Failure/Error: visit &quot;/sessions/new&quot;
         NoMethodError:
           undefined method `visit&#39; for #&lt;RSpec::Core::ExampleGroup::Nested_1:0x16529f8 @example=nil&gt;
         # ./spec/features/security_spec.rb:4:in `(root)&#39;
    
     Finished in 0.006 seconds
     1 example, 1 failure

    Failed examples:

    rspec ./spec/features/security_spec.rb:3 # security signs users in

I think its important to note that at first I was using the URL Helper &#39;new_sessions_path&#39; and it kept giving me an error `undefined local variable or method &#39;new_sessions_path&#39;`. I know it is valid because:
&lt;!-- language-all: lang-rb --&gt;

    $ rake routes
    logout_sessions GET    /sessions/logout(.:format) sessions#logout
           sessions POST   /sessions(.:format)        sessions#create
       new_sessions GET    /sessions/new(.:format)    sessions#new
          contracts POST   /contracts(.:format)       contracts#create
      new_contracts GET    /contracts/new(.:format)   contracts#new
     edit_contracts GET    /contracts/edit(.:format)  contracts#edit
                    GET    /contracts(.:format)       contracts#show
                    PUT    /contracts(.:format)       contracts#update
                    DELETE /contracts(.:format)       contracts#destroy
               root        /                          contracts#index

My Gemfile:
&lt;!-- language-all: lang-rb --&gt;

    source &#39;https://rubygems.org&#39;

    gem &#39;rails&#39;, &#39;3.2.11&#39;
    gem &#39;execjs&#39;

    group :assets do
      gem &#39;sass-rails&#39;,   &#39;~&gt; 3.2.3&#39;
      gem &#39;coffee-rails&#39;, &#39;~&gt; 3.2.1&#39;
      gem &#39;uglifier&#39;, &#39;&gt;= 1.0.3&#39;
    end

    gem &#39;jquery-rails&#39;
    gem &#39;activerecord-oracle_enhanced-adapter&#39;, &#39;~&gt; 1.4.1&#39;
    gem &#39;jruby-openssl&#39;
    gem &#39;therubyrhino&#39;
    gem &#39;kaminari&#39;
    gem &#39;nokogiri&#39;

    group :development do
      gem &#39;warbler&#39;
    end

    group :test do
      gem &#39;rspec-rails&#39;
      gem &#39;capybara&#39;
      gem &#39;activerecord-jdbcsqlite3-adapter&#39;
    end


spec_helper.rb inside of my_app/spec:
&lt;!-- language-all: lang-rb --&gt;

    # This file is copied to spec/ when you run &#39;rails generate rspec:install&#39;
    ENV[&quot;RAILS_ENV&quot;] ||= &#39;test&#39;
    require File.expand_path(&quot;../../config/environment&quot;, __FILE__)
    require &#39;rspec/rails&#39;
    require &#39;rspec/autorun&#39;

    # Capybara integration
    require &#39;capybara/rspec&#39;
    require &#39;capybara/rails&#39;

    # Requires supporting ruby files with custom matchers and macros, etc,
    # in spec/support/ and its subdirectories.
    Dir[Rails.root.join(&quot;spec/support/**/*.rb&quot;)].each {|f| require f}

    RSpec.configure do |config|
      # Remove this line if you&#39;re not using ActiveRecord or ActiveRecord fixtures
      # config.fixture_path = &quot;#{::Rails.root}/spec/fixtures&quot;
      config.use_transactional_fixtures = true
      config.infer_base_class_for_anonymous_controllers = false
      config.order = &quot;random&quot;
      # Include path helpers
      config.include Rails.application.routes.url_helpers
    end


my_app/spec/features/security_spec.rb:
&lt;!-- language-all: lang-rb --&gt;

    describe &quot;security&quot;, :type =&gt; :feature do
      it &quot;signs users in&quot; do
        visit &quot;/sessions/new&quot;
        fill_in &quot;username&quot;, :with =&gt; &quot;user&quot;
        fill_in &quot;password&quot;, :with =&gt; &quot;pass&quot;
        click_button &quot;Sign In&quot;

        page.should have_content(&#39;Login Successful&#39;)
      end
    end

I&#39;ve tried defining the test above both with and without `:type =&gt; :feature`. It makes no difference either way. Any ideas what I should try next?

undefined method `visit&#39; when using RSpec and Capybara in rails

With Observers officially [removed from Rails 4.0](https://github.com/rails/rails-observers), I&#39;m curious what other developers are using in their place. (Other than using the extracted gem.) While Observers were certainly abused and could easily become unwieldily at times, there were many use-cases outside of just cache-clearing where they were beneficial.

Take, for example, an application that needs to track changes to a model. An Observer could easily watch for changes on Model A and record those changes with Model B in the database. If you wanted to watch for changes across several models, then a single observer could handle that. 

In Rails 4, I&#39;m curious what strategies other developers are using in place of Observers to recreate that functionality. 

Personally, I&#39;m leaning towards a sort of &quot;fat controller&quot; implementation, where these changes are tracked in each models controller&#39;s create/update/delete method. While it bloats the behavior of each controller slightly, it does help in readability and understanding as all the code is in one place. The downside is that there&#39;s now code that is very similar scattered throughout several controllers. Extracting that code into helper methods is an option, but you&#39;re still left with calls to those methods littered everywhere. Not the end of the world, but not quite in the spirit of &quot;skinny controllers&quot; either. 

ActiveRecord callbacks are another possible option, though one I don&#39;t personally like as it tends to couple two different models too closely together in my opinion. 

So in the Rails 4, no-Observers world, if you had to create a new record after another record was created/updated/destroyed, what design pattern would you use? Fat controllers, ActiveRecord callbacks, or something else entirely? 

Thank you.

Rails Observer Alternatives for 4.0

I am following the rails tutorial videos and I can&#39;t figure out what the `db:test:prepare` command actually does. Can someone provide an explanation? 

What does rake db:test:prepare actually do?

What is the conceptual difference between Rspec&#39;s [feature specs](https://www.relishapp.com/rspec/rspec-rails/v/2-13/docs/feature-specs/feature-spec) and [request specs](https://www.relishapp.com/rspec/rspec-rails/v/2-13/docs/request-specs/request-spec)?

From the feature spec docs:

&gt; Feature specs are high-level tests meant to exercise slices of functionality
through an application. They should drive the application only via its
external interface, usually web pages.

And for request specs:
&gt; Request specs provide a thin wrapper around Rails&#39; integration tests, and are
designed to drive behavior through the full stack, including routing
(provided by Rails) and without stubbing (that&#39;s up to you).
With request specs, you can:

&gt; - specify a single request
&gt; - specify multiple requests across multiple controllers
&gt; - specify multiple requests across multiple sessions

I know that feature specs use [Capybara](http://jnicklas.github.com/capybara/) and request specs do not. But that hardly merits different concepts.

RSpec: What is the difference between a feature and a request spec?

I&#39;m trying to run a query of about 50,000 records using ActiveRecord&#39;s `find_each` method, but it seems to be ignoring my other parameters like so:

    Thing.active.order(&quot;created_at DESC&quot;).limit(50000).find_each {|t| puts t.id }

Instead of stopping at 50,000 I&#39;d like and sorting by `created_at`, here&#39;s the resulting query that gets executed over the *entire* dataset:

    Thing Load (198.8ms)  SELECT &quot;things&quot;.* FROM &quot;things&quot; WHERE &quot;things&quot;.&quot;active&quot; = &#39;t&#39; AND (&quot;things&quot;.&quot;id&quot; &gt; 373343) ORDER BY &quot;things&quot;.&quot;id&quot; ASC LIMIT 1000

Is there a way to get similar behavior to `find_each` but with a total max limit and respecting my sort criteria?

Content Type	Original Author	Original Content on Stackoverflow
Question	Serge Vinogradoff	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	Dylan Markow	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	Antonio Jha	View Answer on Stackoverflow
Solution 3 - Ruby on-Rails	Soumitra Sarkar	View Answer on Stackoverflow

remove a blank option of select field that was generated by SimpleForm

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

Solution 3 - Ruby on-Rails

AtomicInteger.incrementAndGet() vs. AtomicInteger.getAndIncrement()

How to calculate the 95% confidence interval for the slope in a linear regression model in R

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