Use the `&lt;%# %&gt;` sequence, e.g.

    &lt;%# This is a great comment! %&gt;

For Record

    &lt;%# This is a great comment! %&gt;
    
    &lt;%#= This is a great comment! %&gt;

For block comments:

   

    &lt;% if false %&gt;
        code to be commented out...
    &lt;% end %&gt; 




I have a Windows setup, and this &lt;%-# %&gt; sequence is the only one that works for me:

Example:

    &lt;%-# This is a sample comment! %&gt;



In my text editor, i run `command + /` (sublime-text shortcut). It will be like this.

    &lt;%
    =begin%&gt;
        Here is the comment 
    &lt;%
    =end%&gt;

It doesn&#39;t look simply, but it works.

Since .erb is by definition &quot;embedded ruby&quot;, you can embed every ruby code between: `&lt;%=`  and the other: `%&gt;`, typically all written in one line. In addition, ruby one-line comments start always with `#`, so the `&lt;%=# Comment %&gt;` style matches perfectly with both pure-ruby and erb styles for one-line comments.

I doesn&#39;t work in the Controllers files, I had to put it between slashes

/ comment here.... /  


&lt;!-- language: lang-ruby --&gt;

    obj.update_attribute(:only_one_field, &#39;Some Value&#39;)
    obj.update_attributes(field1: &#39;value&#39;, field2: &#39;value2&#39;, field3: &#39;value3&#39;)

Both of these will update an object without having to explicitly tell ActiveRecord to update.

Rails API says:

&gt; update_attribute
&gt;
&gt; Updates a single attribute and saves the record without going through the normal validation procedure. This is especially useful for boolean flags on existing records. The regular update_attribute  method in Base is replaced with this when the validations module is mixed in, which it is by default.

&gt; update_attributes
&gt; 
&gt; Updates all the attributes from the passed-in Hash and saves the record. If the object is invalid, the saving will fail and false will be returned. 

So if I don&#39;t want to have the object validated I should use `#update_attribute`. What if I have this update on a `#before_save`, will it stackoverflow?

My question is does `#update_attribute` also bypass the before save or just the validation.

Also, what is the correct syntax to pass a hash to `#update_attributes` ... check out my example at the top.




Rails: #update_attribute vs #update_attributes

I have a directory of ZIP files (created on a Windows machine). I can manually unzip them using `unzip filename`, but how can I unzip all the ZIP files in the current folder via the shell?

Using Ubuntu Linux Server.

Unzip All Files In A Directory

How do we add comments in erb files, if we do not want them to be generated into the html content? 

Best way to add comments in erb

<p>How do we add comments in erb files, if we do not want them to be generated into the html content?</p>


Say I have a router helper that I want more info on, like blogs_path, how do I find out the map statements behind that in console.

I tried generate and recognize and I got unrecognized method error, even after I did require &#39;config/routes.rb&#39;

Recognize routes in rails console Session

I am wondering what is a convenient function in Rails to convert a string with a negative sign into a number. e.g. `-1005.32`

When I use the `.to_f` method, the number becomes `1005` with the negative sign and decimal part being ignored.

rails convert string to number

Please explain the difference between 
has_and_belongs_to_many and has_many through relationship. When and where to use which one?

has_and_belongs_to_many vs has_many through

When do you use `attr_reader`/`attr_writer`/`attr_accessor` in Rails models?


usage of attr_accessor in Rails

I need to read the data out of database and then save it in a text file.

How can I do that in Ruby? Is there any file management system in Ruby?

How to write to file in Ruby?

In rails guides it&#39;s described like this:

&gt;Objects will be in addition destroyed if they’re associated with `:dependent =&gt; :destroy`, and deleted if they’re associated with `:dependent =&gt; :delete_all`

Right, cool. But what&#39;s the difference between being destroyed and being deleted?
I tried both and it seems to do the same thing.

Rails :dependent =&gt; :destroy VS :dependent =&gt; :delete_all

It is said that when we have a class `Point` and knows how to perform `point * 3` like the following:

    class Point
      def initialize(x,y)
        @x, @y = x, y
      end
    
      def *(c)
        Point.new(@x * c, @y * c)
      end
    end
    
    point = Point.new(1,2)
    p point
    p point * 3

Output:

    #&lt;Point:0x336094 @x=1, @y=2&gt;
    #&lt;Point:0x335fa4 @x=3, @y=6&gt;

but then, 

    3 * point

is not understood:

&gt; `Point` can&#39;t be coerced into `Fixnum` (`TypeError`)

So we need to further define an instance method `coerce`:

    class Point
      def coerce(something)
        [self, something]
      end
    end
    
    p 3 * point

Output:

    #&lt;Point:0x3c45a88 @x=3, @y=6&gt;

So it is said that `3 * point` is the same as `3.*(point)`. That is, the instance method `*` takes an argument `point` and invoke on the object `3`.

Now, since this method `*` doesn&#39;t know how to multiply a point, so

    point.coerce(3)

will be called, and get back an array:

    [point, 3]

and then `*` is once again applied to it, is that true?

Now, this is understood and we now have a new `Point` object, as performed by the instance method `*` of the `Point` class.

The question is:

1. Who invokes `point.coerce(3)`? Is it Ruby automatically, or is it some code inside of `*` method of `Fixnum` by catching an exception?  Or is it by `case` statement that when it doesn&#39;t know one of the known types, then call `coerce`?

2. Does `coerce` always need to return an array of 2 elements?  Can it be no array?  Or can it be an array of 3 elements?

3. And is the rule that, the original operator (or method) `*` will then be invoked on element 0, with the argument of element 1?  (Element 0 and element 1 are the two elements in that array returned by `coerce`.)   Who does it?  Is it done by Ruby or is it done by code in `Fixnum`?  If it is done by code in `Fixnum`, then it is a &quot;convention&quot; that everybody follows when doing a coercion?

  So could it be the code in `*` of `Fixnum` doing something like this:

        class Fixnum
          def *(something)
            if (something.is_a? ...)
            else if ...  # other type / class
            else if ...  # other type / class
            else
            # it is not a type / class I know
              array = something.coerce(self)
              return array[0].*(array[1])   # or just return array[0] * array[1]
            end
          end
        end

4. So it is really hard to add something to `Fixnum`&#39;s instance method `coerce`?  It already has a lot of code in it and we can&#39;t just add a few lines to enhance it (but will we ever want to?)

5. The `coerce` in the `Point` class is quite generic and it works with `*` or `+` because they are transitive.  What if it is not transitive, such as if we define Point minus Fixnum to be:

        point = Point.new(100,100)
        point - 20  #=&gt; (80,80)
        20 - point  #=&gt; (-80,-80)

In Ruby, how does coerce() actually work?

How can I comment multiple lines in Ruby?

Multi-Line Comments in Ruby?

In Bash, # is used to comment the following. How do I make a comment on the Windows command line?



How do I comment on the Windows command line?

Is it correct practice to add Javadoc comments in the interface and add non-Javadoc comments in the implementation?

Most IDEs generate non-JavaDoc comments for implementations when you auto generate comments. Shouldn&#39;t the concrete method have the description?


Should Javadoc comments be added to the implementation?

How do you comment out html mixed with ruby code?

    some text &lt;% ... %&gt; more text &lt;%= ... %&gt;
    something else
    &lt;% ... %&gt;

In jsp it&#39;s real simple: `&lt;%-- ... --%&gt;`, but I&#39;m unable to find any concise option in rails.

Simple html comments `&lt;!-- ... --&gt;` do not work: ruby code is still executed and yells errors.  

There&#39;s an option to use `if false` with html comments, but it&#39;s quite verbose, not to mention IDEs doesn&#39;t support it.

There&#39;s also an option coming from pure ruby, which surprisingly works.

    &lt;%
    =begin %&gt;
    ... html and ruby code goes here
    &lt;%
    =end %&gt;

It&#39;s generally fine, except that it&#39;s verbose, weird-looking and none of ruby IDEs I know support it (yep, I like to comment/comment-out with one keystroke).

I&#39;m curious, is there any &#39;official&#39; of doing this in rails?

Thanks!

Block comments in html.erb templates in rails

How do I comment this Enum so that the warning does not appear? Yes I realize that comments are unnecessary, but if commenting is easy and it resolves the warnings then I&#39;d like to do it. 

Warnings that appear:
Missing XML comment for publicly visible type or member

    /// &lt;summary&gt;
    /// Conditional statements
    /// &lt;/summary&gt;
    public enum ConditionType
    {
        Equal,
        NotEqual,
        GreaterThan,
        GreaterThanOrEqual,
        LessThan,
        LessThanOrEqual
    }

How do I comment a publicly visible type Enum?

Suppose I have the following string 

    @x = &quot;&lt;a href=&#39;#&#39;&gt;Turn me into a link&lt;/a&gt;&quot;

In my view, I want a link to be displayed. That is, I don&#39;t want everything in @x to be unescaped and displayed as a string. What&#39;s the difference between using

    &lt;%= raw @x %&gt;
    &lt;%= h @x %&gt;
    &lt;%= @x.html_safe %&gt;

?

raw vs. html_safe vs. h to unescape html

Why is the view of Rails application in the format `*.erb.html`? What does &quot;erb&quot; mean?

What is the meaning of erb?

I tried `:include_blank =&gt; true`, but it didn&#39;t work.

    &lt;select&gt;
        &lt;%= options_for_select Model.all.collect{|mt| [mt.name, mt.id]} %&gt;
    &lt;/select&gt;

If I need to add it to the collection, how would you do that?

Include blank for first item in select list in options_for_select tag

Can some one please describe the usage of the following characters which is used in ERB file:

    &lt;%   %&gt;
    &lt;%=  %&gt;
    &lt;%  -%&gt;
    &lt;%#  %&gt;

what&#39;s the usage of each one ? 

What is the difference between &lt;%, &lt;%=, &lt;%# and -%&gt; in ERB in Rails?

In what ways can you comment in CoffeeScript?

The documentation say you can use three hash symbols to start and close a comment block:

    ###
      Comments
      go
      here
    ###

I&#39;ve found that I can sometimes use the following two formats

    `// backticks allow for straight-JavaScript,
     // but the closing backtick can&#39;t be on a comment line (I think?)
    `

Are there a simpler way to insert short comments in CoffeeScript?

Do NOT use this style**

Since this is getting a lot of views, I want to emphasize that

    /* Comment goes here */

produces a MATH error when the `/*` is on its own line.

As Trevor pointed out in a comment on the question, this is a **regular expression**, **NOT** a comment!


Content Type	Original Author	Original Content on Stackoverflow
Question	Kalyan Maddu	View Question on Stackoverflow
Solution 1 - Ruby on-Rails	John Douthat	View Answer on Stackoverflow
Solution 2 - Ruby on-Rails	Salil	View Answer on Stackoverflow
Solution 3 - Ruby on-Rails	Tim	View Answer on Stackoverflow
Solution 4 - Ruby on-Rails	Edward Castaño	View Answer on Stackoverflow
Solution 5 - Ruby on-Rails	Miftah Mizwar	View Answer on Stackoverflow
Solution 6 - Ruby on-Rails	Maaaaaaarco	View Answer on Stackoverflow
Solution 7 - Ruby on-Rails	Arezki	View Answer on Stackoverflow

Best way to add comments in erb

Ruby on-Rails Problem Overview

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

Solution 2 - Ruby on-Rails

Solution 3 - Ruby on-Rails

Solution 4 - Ruby on-Rails

Solution 5 - Ruby on-Rails

Solution 6 - Ruby on-Rails

Solution 7 - Ruby on-Rails

Unzip All Files In A Directory

Rails: #update_attribute vs #update_attributes

Attributions