Fix records_count when using group by

[smridge]

Changes

• Fixed records_count to handle hashes (typically returned with group). As it stands, only ActiveRecord_Relation are handled. This fix ensures an integer is always returned.
• Changed count to size to avoid any misleadings / documentation collisions.
• Fixes Extending unscope? #8

Detail

Currently, when using select to load custom attributes that are grouped on the Model, the count breaks when evaluating @page.last?. Specifically, this breaks on while residual > 0 with the error of no implicit conversion of Integer into Hash.

After looking at the method-i-count docs

If count is used with Relation#group for multiple columns, it returns a Hash whose keys are an array containing the individual values of each column and the value of each key would be the count.

This explains the quirk.

Example usage:

# in model
scope :with_custom_selections, lambda {
  joins(:bars).select(
    <<~SQL.squish
      foos.*,
      count(bars.id) as bars_count
    SQL
  ).group(:id)
}

# in controller
@foos = set_page_and_extract_portion_from(Foo.with_custom_selections)

# in view
<% if @page.last? %>
...

[antonlitvinenko]

I think, this is very inefficient: imagine a model with millions of records... to_a would load them all. This feels like a hack, but should a little bit better:

    def records_count
      if @records_count.nil?
        @records_count = records.unscope(:limit).unscope(:offset).unscope(:select).count
        # records count could be a hash if query has a group by clause -> in this case records count is number of groups
        @records_count = @records_count.size if @records_count.is_a?(Hash)
      end

      @records_count
    end

[smridge]

Great callout! I've updated the code and PR description.

[koddsson]

Just hit this in our codebase and we've currently got it monkey-patched. It would be great to remove that patch with these changes merged upstream 🙏🏻