Why does Relation.size sometimes return a Hash in Rails 4 - ruby-on-rails-4

Question

I can run a query in two different ways to return a Relation.
When I interrogate the size of the Relation one query gives a Fixnum as expected the other gives a Hash which is a hash of each value in the Relations Group By statement with the number of occurrences of each.
In Rails 3 I assume it always returned a Fixnum as I never had a problem whereeas with Rails 4 it sometimes returns a Hash and a statement like Rel.size.zero? gives the error:
undefined method `zero?' for {}:Hash
Am I best just using the .blank? method to check for zero records to be sure of avoiding unexpected errors?
Here is a snippet of code with looging statements for the two queries and the resulting log
CODE:
assessment_responses1=AssessmentResponse.select("process").where("client_id=? and final = ?",self.id,false).group("process")
logger.info("-----------------------------------------------------------")
logger.info("assessment_responses1.class = #{assessment_responses1.class}")
logger.info("assessment_responses1.size.class = #{assessment_responses1.size.class}")
logger.info("assessment_responses1.size value = #{assessment_responses1.size}")
logger.info("............................................................")
assessment_responses2=AssessmentResponse.select("distinct process").where("client_id=? and final = ?",self.id,false)
logger.info("assessment_responses2.class = #{assessment_responses2.class}")
logger.info("assessment_responses2.size.class = #{assessment_responses2.size.class}")
logger.info("assessment_responses2.size values = #{assessment_responses2.size}")
logger.info("-----------------------------------------------------------")
LOG
-----------------------------------------------------------
assessment_responses1.class = ActiveRecord::Relation::ActiveRecord_Relation_AssessmentResponse
(0.5ms) SELECT COUNT(`assessment_responses`.`process`) AS count_process, process AS process FROM `assessment_responses` WHERE `assessment_responses`.`organisation_id` = 17 AND (client_id=43932 and final = 0) GROUP BY process
assessment_responses1.size.class = Hash
CACHE (0.0ms) SELECT COUNT(`assessment_responses`.`process`) AS count_process, process AS process FROM `assessment_responses` WHERE `assessment_responses`.`organisation_id` = 17 AND (client_id=43932 and final = 0) GROUP BY process
assessment_responses1.size value = {"6 Month Review(1)"=>3, "Assessment(1)"=>28, "Assessment(2)"=>28}
............................................................
assessment_responses2.class = ActiveRecord::Relation::ActiveRecord_Relation_AssessmentResponse
(0.5ms) SELECT COUNT(distinct process) FROM `assessment_responses` WHERE `assessment_responses`.`organisation_id` = 17 AND (client_id=43932 and final = 0)
assessment_responses2.size.class = Fixnum
CACHE (0.0ms) SELECT COUNT(distinct process) FROM `assessment_responses` WHERE `assessment_responses`.`organisation_id` = 17 AND (client_id=43932 and final = 0)
assessment_responses2.size values = 3
-----------------------------------------------------------

Answer 1

size on an ActiveRecord::Relation object translates to count, because the former tries to get the count of the Relation. But when you call count on a grouped Relation object, you receive a hash.
The keys of this hash are the grouped column's values; the values of this hash are the respective counts.
AssessmentResponse.group(:client_id).count # this will return a Hash
AssessmentResponse.group(:client_id).size # this will also return a Hash
This is true for the following methods: count, sum, average, maximum, and minimum.
If you want to check for rows being present or not, simply use exists? i.e. do the following:
AssessmentResponse.group(:client_id).exists?
Instead of this:
AssessmentResponse.group(:client_id).count.zero?