Rails: Count specific records then do calculation

Question

I am attempting to do a rails record count then do a calculation from those records to give me a final number:

Example

100 Records = A
30 Records = B
Total Records = C

A+(-B)=C

I am not even going to show you what I tried... in retrospect I am very new to rails and it made no logical sense!

UPDATE: To further expand:

When implementing this I realized that there might be some slight difference from what it solves above. I have a MVC called "POST" It was some records within the table one specifically is called "VOTE" the vote integer will consist of 1 or (-1). Each post will have a VOTE column that represent a value of 1 or (-1). I am trying to create an analytic metric that consists of the following:

TOTAL = (Total posts with Value 1) + (Total posts with Value -1) Example

1234 = 2000 + (-776)

Thank you in advance!

Answer 1

In general, C = A.count + B.count

If you want C to be the union of A and B, then do

C = A & B
C.count # Number of elements in C

For your specific case:

yes_votes = POST.where('VOTE = ?', 1)
no_votes = POST.where('VOTE = ?', -1)
total = yes_votes.count - no_votes.count