Rails - Apr 2010 - count(*) in find :select returns a String? Why not Fixnum?

>> clicks = Click.find(:all,:select=>"count(*) as count,
date", :group=>"date")
=> [#<Click date: "2010-04-05">, #<Click date:
"2010-04-06">, #<Click
date: "2010-04-07">]
>> clicks[0].count.class
=> String

Should this return a String?  I would think it would surely be a Fixnum.
Am I crazy?  Is this a bug in rails?

Anyone know a way to get around this?  I need to make it a Fixnum or
Float using count(*) in find.  Casting it using to_i after the fact will
not work in my scenario.  I need to this to be correct when it returns
the "clicks" array.
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On Wed, Apr 7, 2010 at 8:27 AM, Yanni Mac
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
>>> clicks = Click.find(:all,:select=>"count(*) as count,
date", :group=>"date")
> => [#<Click date: "2010-04-05">, #<Click date:
"2010-04-06">, #<Click
> date: "2010-04-07">]
>
>>> clicks[0].count.class
> => String
>
> Should this return a String?  I would think it would surely be a Fixnum.
> Am I crazy?  Is this a bug in rails?
I believe ''clicks'' is not what you think it is.

Try using `inspect` to examine clicks, clicks[0], etc.

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On 7 April 2010 16:27, Yanni Mac
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
>>> clicks = Click.find(:all,:select=>"count(*) as count,
date", :group=>"date")
> => [#<Click date: "2010-04-05">, #<Click date:
"2010-04-06">, #<Click
> date: "2010-04-07">]
>
>>> clicks[0].count.class
> => String
>
> Should this return a String?  I would think it would surely be a Fixnum.
> Am I crazy?  Is this a bug in rails?
>
> Anyone know a way to get around this?  I need to make it a Fixnum or
> Float using count(*) in find.  Casting it using to_i after the fact will
> not work in my scenario.  I need to this to be correct when it returns
> the "clicks" array.
Create a method that returns what you want (by manipulating the string
however is needed). particularly if you are likely to ever to need
this number in two places in the code - abstract it to stay DRY:

# your model
def click_count
  Click.find(:all,:select=>"count(*) as count, date",
:group=>"date").first.count.to_i
end

# or on the Click model
def self.click_count
  Click.find(:all,:select=>"count(*) as count, date",
:group=>"date").first.count.to_i
end

so you can use your_model.click_count, or Click.click_count and be
returned an integer.


But would you not be better using the AR "Model.count" method rather
than changing the select condition of .find?
http://api.rubyonrails.org/classes/ActiveRecord/Calculations/ClassMethods.html#M002187

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Hassan, thanks for quick the reply.

I am not really sure what you mean by this, though.  The above example 
shows that clicks returns an array of clicks.  I am just taking the 
first click object and seeing what data type it is using .class

Here is a closer look at the first object in the array.  As you can see, 
Rails converted "count(*) as count" to a String.
>> clicks[0].attributes
=> {"date"=>Mon, 05 Apr 2010,
"count"=>"1"}

Maybe this is a MySQL issue.. I am testing right now to see what the 
data type of count(*) is from mysql.
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> # your model
> def click_count
>   Click.find(:all,:select=>"count(*) as count, date",
> :group=>"date").first.count.to_i
> end
> 
> # or on the Click model
> def self.click_count
>   Click.find(:all,:select=>"count(*) as count, date",
> :group=>"date").first.count.to_i
> end
> 
> so you can use your_model.click_count, or Click.click_count and be
> returned an integer.
> 
Michael, thanks for the reply.

Getting the first row click count does not really help since I am 
grouping by date.  This find statement will return many rows.

Example:
Date | Count
jan 1, 5
jan 2, 6
jan 3, 2

I could iterate thru each date and perform the find count, but that is 
extremely inefficient.
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On 7 April 2010 16:58, Yanni Mac
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Getting the first row click count does not really help since I am
> grouping by date.  This find statement will return many rows.
>
> Example:
> Date | Count
> jan 1, 5
> jan 2, 6
> jan 3, 2
>
> I could iterate thru each date and perform the find count, but that is
> extremely inefficient.
Ah! Sorry... missed that.

Just a thought... can you be sneaky and add an accessor method to Click?

# Click model
def count
  read_attribute(:count).to_i rescue nil
end


No idea if it''ll work... maybe worth a bash...

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I am also not crazy about using Model.count, because it just returns an 
ordered hash.  Some of my code is dependant on using AR classes when 
manipulating this data set... might just have to deal with it though and 
code a workaround.
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Michael Pavling wrote:
> On 7 April 2010 16:58, Yanni Mac
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
>> extremely inefficient.
> Ah! Sorry... missed that.
> 
> Just a thought... can you be sneaky and add an accessor method to Click?
> 
> # Click model
> def count
>   read_attribute(:count).to_i rescue nil
> end
> 
> 
> No idea if it''ll work... maybe worth a bash...
Thanks Michael, that got me thinking!  This is a hack, but it still 
works for me because I can call it on one line.  I am developing a 
reporting system where I convert an ActiveRecord object list to a table, 
so I really wanted to avoid hard coding something in each class.  This 
allows me to create my list on one line and then pass it to my 
conversion method.

 Click.find(:all,:select=>"count(*) as click_count, date", 
:group=>"date").each{|c|c.click_count = c.click_count.to_i}

I still want to figure out why count(*) does not return a number data 
type, but this will work for now.
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On 7 April 2010 17:16, Yanni Mac
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> Thanks Michael, that got me thinking!
>
>  Click.find(:all,:select=>"count(*) as click_count, date",
> :group=>"date").each{|c|c.click_count = c.click_count.to_i}
>
You should still look to putting that code in a method somewhere to
avoid duplication.
YMMV

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>
> I still want to figure out why count(*) does not return a number data
> type, but this will work for now.
>
The answer''s quite straight forward - because Rails doesn''t
work that way.

The typecasting for a MySQL attribute to a Ruby class is done in the
read_attribute method in
the activerecord/lib/active_record/attribute_methods.rb file. In that method
you can see they only typecast the value if column_for_attribute returns the
column (i.e. if it''s defined in the schema for the table).

So, your dynamically created column is not in the schema, so it won''t
be
typecast to an integer.

Cheers,


Andy

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On 7 April 2010 17:03, Michael Pavling
<pavling-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Just a thought... can you be sneaky and add an accessor method to Click?
>
> # Click model
> def count
>  read_attribute(:count).to_i rescue nil
> end
>
> No idea if it''ll work... maybe worth a bash...
FYI: This does work. Just tried it here and I get integers returned.
No need to do the extra iteration of each result.

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You might want to try an after_find() or after_initialize() filter for
ActiveRecord. If I remember right they''ll let you coerce the value to
an integer before the object gets returned to the calling code.

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On Wed, Apr 7, 2010 at 9:30 AM, Andy Jeffries
<andyjeffries-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>wrote:
> The typecasting for a MySQL attribute to a Ruby class is done in the
> read_attribute method in
> the activerecord/lib/active_record/attribute_methods.rb file. In that
method
> you can see they only typecast the value if column_for_attribute returns
the
> column (i.e. if it''s defined in the schema for the table).
>
>
Excellent info, this little tibdit helps me, too, coming to Rails for a
mod_perl world where everything is dynamically typed ("1" == 1 etc).
The
typecasting logic of ActiveRecord has been a learning curve.

Anyone know of a more detailed description of how the typecasting workflow
works, from ActiveRecord down to the MySQL level? That''d be a super
useful
document/overview to have. Each layer (app, activerecord, ruby mysql client,
mysql itself) will have it''s own concerns on this chain of events.

In certain versions of MySQL, the typecasting can become extremely
important, due to strange bugs in MySQL. For instance, if you do something
like

"select * from mytable where id > ''1234''"

and 1234 is an integer column but you''ve put in quotes (i.e. a string)
for
the query, and it is outside the bounds of the index on id, MySQL will
resort to a table scan. i saw this bug wreak havoc on a large rig once, in
mod_perl world where the database adapter put quotes around integers.

But that''s just an example of how fully understanding typecasting from
top-down can be a really useful thing.

jsw

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>
> The typecasting for a MySQL attribute to a Ruby class is done in the
>> read_attribute method in
>> the activerecord/lib/active_record/attribute_methods.rb file. In that
method
>> you can see they only typecast the value if column_for_attribute
returns the
>> column (i.e. if it''s defined in the schema for the table).
>>
>
> Excellent info, this little tibdit helps me, too, coming to Rails for a
> mod_perl world where everything is dynamically typed ("1" == 1
etc). The
> typecasting logic of ActiveRecord has been a learning curve.
>
Just to be clear, I''m not a Rails-core developer, I''m just a
happy user of
apidock.com.  If you go to apidock.com/rails you can search for Rails
functions, see other user''s comments and click "View Source"
to see the
methods source.  It''s often a good starting point in to trying to read
the
Rails source code (which is actually very readable if you know Ruby).

If you read either of the books Ruby Best Practices or Metaprogramming Ruby
you''ll be good to go in reading the Rails source code (I''d
possibly say the
latter is slightly better for this purpose).

Cheers,


Andy

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