That's the point, relation.count will *always* perform a COUNT on database.
On Mon, Sep 15, 2014 at 8:50 AM, Will Bryant <will.bry...@gmail.com> wrote:
> Yes, but it will have to *load* all the rows from the database into ruby.
> If we have a table with a few million of rows, which is pretty small for a
> real app, and we're doing a join and a group to get the count of some
> associated record, then calling .values.sum would load all those millions
> of rows, and then add up the values.
>
> Returning the millions of rows (even if it was just the IDs and counts) is
> many orders of magnitude slower than getting the database to tell us how
> many rows would be in the rowset, and it's going to use a lot of memory too.
>
> Yes, if your app only has thousands of rows, then it won't matter. But
> this is not a good argument for a database library to be inefficient.
>
> The point is that count should always return a count of the results in a
> relation, irrespective of what is involved in the relation. That's the
> point of relational algebra; you can combine two operations and you get the
> logical composite.
>
> Returning the count of each grouping is a logically separate thing to do,
> and it should have a separate API call.
>
>
> On 15/09/2014, at 23:36 , G. Sobrinho <gabriel.sobri...@gmail.com> wrote:
>
> I'm not sure if you get what .values.sum would do:
>
> c = User.group(:role).count
> => {:normal=>3, :admin=>4}
>
> c.values.sum
> => 7
>
>
> Even a hash with thousands of keys/values would sum its values very fast.
>
>
> And I don't get what you mean with "is actually changing what would be
> counted".
>
> Considering c = User.group(:role).count, c.values.sum would return the
> exactly number of records that would be returned and c.keys.sum would
> return exactly number of group param that would be returned, no?
>
> On Sun, Sep 14, 2014 at 2:20 AM, Will Bryant <will.bry...@gmail.com>
> wrote:
>
>> Calling .values.sum might have to load a LOT of (id, count) rows so it
>> isn't a very scalable solution.
>>
>> Calling regroup or something is actually changing what would be counted -
>> the group can affect the count, especially if you use HAVING clauses.
>>
>> There's nothing wrong with having the grouped count functionality, but
>> it's messing up the #count API IMHO.
>>
>>
>> On 13/09/2014, at 03:40 , Gabriel Sobrinho <gabriel.sobri...@gmail.com>
>> wrote:
>>
>> I'm against to count and size works equally since I would want to know
>> how many grouped records do I have (i.e.: how many roles do I have on
>> determining relation).
>>
>> I think that count and size is working as both should.
>>
>>
>> Although, if you want to count all records of a grouped relation, you
>> have to remove the group or just sum the counts:
>>
>> User.count
>>
>>
>> or:
>>
>>
>>
>> User.group(:role).count.values.sum
>>
>>
>> Not elegant but if you can't remove the group for that count, you have to
>> do that.
>>
>>
>> One possible option would rails have something like regroup(false) as
>> reorder(false), but again I think that just adding the values is more
>> easier for everyone :)
>>
>> On Thursday, September 11, 2014 11:54:14 PM UTC-3, Shinohara Teruki wrote:
>>>
>>> >> size in this case is an pretty much an "alias" for count, thus it's
>>> gonna work the same way as count when grouping.
>>>
>>> I think that current #size don't behave like an alias for #count.
>>>
>>> g = User.group(:role); g.load; g.count
>>> => {:normal=>3, :admin=>4}
>>>
>>> g = User.group(:role); g.load; g.size
>>> => 2
>>>
>>> When I call #load before #count or #size, a return value of #count don't
>>> equals to a return value of #size.
>>>
>>>
>>> >> Is there any particular reason to know how many records returned if
>>> you are grouping?
>>>
>>> I expect #count and #size to return same value.
>>> It is not the case that I want to know how many records the grouping
>>> query returns.
>>>
>>> My ideal implementation:
>>>
>>> g = User.group(:role); g.load; g.count
>>> => {:normal=>3, :admin=>4}
>>>
>>> g = User.group(:role); g.load; g.size
>>> =>{:normal=>3, :admin=>4}
>>>
>>> or
>>>
>>> g = User.group(:role); g.load; g.count
>>> => 2
>>>
>>> g = User.group(:role); g.load; g.size
>>> =>2
>>>
>>> What do you think?
>>>
>>> Thank you
>>>
>>>
>>> 2014年9月12日金曜日 8時21分39秒 UTC+9 Carlos Antonio da Silva:
>>>>
>>>> size in this case is an pretty much an "alias" for count, thus it's
>>>> gonna work the same way as count when grouping.
>>>>
>>>> Is there any particular reason to know how many records returned if you
>>>> are grouping?
>>>>
>>>> On Wed, Sep 10, 2014 at 11:16 AM, Shinohara Teruki <ts....@gmail.com>
>>>> wrote:
>>>>
>>>>> ActiveRecord::Relation.size returns a Hash when I use a group method.
>>>>> I think that a size method is expected to return integer typically.
>>>>>
>>>>> I propose this implementation:
>>>>>
>>>>> def size
>>>>> if loaded?
>>>>> @records.length
>>>>> else
>>>>> count_value = count(:all)
>>>>> count_value.is_a?(Hash) ? count_value.length : count_value
>>>>> end
>>>>> end
>>>>>
>>>>> This is a current implementation:
>>>>>
>>>>> # https://github.com/rails/rails/blob/master/activerecord/lib/active_
>>>>> record/relation.rb
>>>>> # Returns size of the records.
>>>>> def size
>>>>> loaded? ? @records.length : count(:all)
>>>>> end
>>>>>
>>>>>
>>>>> A count method is implemented on calculations.rb.
>>>>> https://github.com/rails/rails/blob/master/activerecord/lib/active_
>>>>> record/relation/calculations.rb
>>>>>
>>>>>
>>>>> What do you think?
>>>>>
>>>>> Thank you
>>>>>
>>>>> --
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>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> At.
>>>> Carlos Antonio
>>>>
>>>
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>
>
>
> --
> Cheers,
>
> Gabriel Sobrinho
> http://gabrielsobrinho.com/
>
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--
Cheers,
Gabriel Sobrinho
http://gabrielsobrinho.com/
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