Grouping in Ruby on Rails using PostGres

Question

I have the following line of code which works in sqlite, but in PostGres doesn't:

@income_by_category = SoldCategory.group(:category_name).having("branch_id=?", @branch_id).sum(:total).to_a

It's basically grouping all the SoldCategory by :category_name that have the same @branch_id, adding all their :total's, and converting it to an array. I'm using it to provide some data to some charts. It gives me a result similar to this:

[['shoes', 5000], ['pants', 6000], ['shirts', 7000]]

How can I achieve the same result using PostGress?

Answer 1

So you want to take all the sold_categories that have a given branch_id and then find the per-category sums? Your approach is a bit off, HAVING is not what you're looking for. The SQL you want is simply this:

select category_name, sum(total)
from sold_categories
where branch_id = ?
group by category_name

and that translates to this with ActiveRecord:

SoldCategory.where(:branch_id => @branch_id).sum(:total, :group => :category_name)

That will give you a nice Hash that looks like this:

{ 'shoes' => 5000, 'pants' => 6000, 'shirts' => 7000 }

Once you have this fixed, your very next step should be to install PostgreSQL in your development environment so that you can develop and deploy using the same database. There are a lot of small differences between databases that no ORM can protect you from; database portability is a myth unless your needs are absurdly simple or you write your own portability layer and test test test test test and test some more and then run more tests to make sure you've tested every code path you use on every database you care about.