ActiveRecord has_many with multiple conditions - sql

Question

I'm trying to find an object by checking for several of its relations.
Loan.joins(:credit_memo_attributes)
.where(credit_memo_attributes: {name: 'pr2_gtx1_y', value: '2014'})
.where(credit_memo_attributes: {name: 'pr1_gtx1_y', value: '2013'})
.where(credit_memo_attributes: {name: 'tx1_y', value: '2014'})
Calling to_sql on that gives:
"SELECT `loans`.* FROM `loans` INNER JOIN `credit_memo_attributes`
ON `credit_memo_attributes`.`loan_id` = `loans`.`id`
WHERE `credit_memo_attributes`.`name` = 'pr2_gtx1_y' AND `credit_memo_attributes`.`value` = '2014'
AND `credit_memo_attributes`.`name` = 'pr1_gtx1_y' AND `credit_memo_attributes`.`value` = '2013'
AND `credit_memo_attributes`.`name` = 'tx1_y' AND `credit_memo_attributes`.`value` = '2014'"
So, I'm checking for Loans that have credit_memo_attributes with all of those attributes. I know at least 1 of our 20,000 loans meets this criteria, but this query returns an empty set. If I only use 1 of the where clauses, it returns several, as I'd expect, but once I add even 1 more, it's empty.
Any idea where I'm going wrong?

Answer 1

Update:
Based on comments I believe you want multiple joins in your criteria. You can do that like this:
attr_1 = {name: 'pr2_gtx1_y', value: '2014'}
attr_2 = {name: 'pr1_gtx1_y', value: '2013'}
attr_3 = {name: 'tx1_y', value: '2014'}
Loan.something_cool(attr_1, attr_2, attr_3)
class Loan < ActiveRecord::Base
...
def self.something_cool(attr_1, attr_2, attr_3)
joins(sanitize_sql(["INNER JOIN credit_memo_attributes AS cma1 ON cma1.loan_id = loans.id AND cma1.name = :name AND cma1.value = :value", attr_1]))
.joins(sanitize_sql(["INNER JOIN credit_memo_attributes AS cma2 ON cma2.loan_id = loans.id AND cma2.name = :name AND cma2.value = :value", attr_2]))
.joins(sanitize_sql(["INNER JOIN credit_memo_attributes AS cma3 ON cma3.loan_id = loans.id AND cma3.name = :name AND cma3.value = :value", attr_3]))
end
If you look at the SQL generated (that you included in your question, thank you) you'll see that all those conditions are being ANDed together. There are NO rows for which name = 'pr2_gtx1_y' AND name = 'pr1_gtx1_y' (and so forth). So you are getting the result I would expect (no rows).

Answer 2

You can put all names and values into array like ids and years and pass those into where clause like this. Active Record will query all the values in the array.
Loan.joins(:credit_memo_attributes)
.where(credit_memo_attributes: {name: ids, value: years})
Personally I'm still learning active record, in this concern i don't think active record supports multiple where clauses.

Answer 3

Notice how the SQL version is returning your code: it is joining the requirements with an AND.
"SELECT `loans`.* FROM `loans` INNER JOIN `credit_memo_attributes`
ON `credit_memo_attributes`.`loan_id` = `loans`.`id`
WHERE `credit_memo_attributes`.`name` = 'pr2_gtx1_y' AND `credit_memo_attributes`.`value` = '2014'
AND `credit_memo_attributes`.`name` = 'pr1_gtx1_y' AND `credit_memo_attributes`.`value` = '2013'
AND `credit_memo_attributes`.`name` = 'tx1_y' AND `credit_memo_attributes`.`value` = '2014'"
Now, this is next to impossible. An Object.name can never be all pr2_gtx1_y, pr1_gtx1_y, and tx1_y. Same goes for the value attributes.
What you need here is an OR as opposed to the AND.
To this effect, try to change your query to the following:
Loan.joins(:credit_memo_attributes)
.where(
"credit_memo_attributes.name = ? and credit_memo_attributes.value = ?
OR credit_memo_attributes.names = ? and credit_memo_attributes.value = ?
OR credit_memo_attributes.name = ? and credit_memo_attributes.value = ?",
'pr2_gtx1_y', '2014',
'pr1_gtx1_y', '2013',
'tx1_y', '2014'
)