Make an IN statement using two attributes in Activerecord - sql

Question

I've been trying this for a while, and can't seem to get it right in Activerecord.
Given an array of asset_id and asset_type pairs, query a class that has both those attributes, only where both asset_id and asset_type match.
So given the array
[[4,"Logo"],[1,"Image"]]
I want to generate the SQL
SELECT "asset_attachments".* FROM "asset_attachments" WHERE ((asset_id,asset_type) IN ((4,'Logo'),(1,'Image')))
I can do this by manually entering a string using where like this:
AssetAttachment.where("(asset_id,asset_type) IN ((4,'Logo'),(1,'Image'))")
But I'm trying to use it with an array of any length and asset type/id.
So far I've tried
AssetAttachment.where([:asset_id, :asset_type] => [[4,"Logo"],[1,"Image"]])
NoMethodError: undefined method `to_sym' for [:asset_id, :asset_type]:Array
and
AssetAttachment.where("(asset_id,asset_type)" => [[4,"Logo"],[1,"Image"]])
ActiveRecord::StatementInvalid: PG::Error: ERROR: column asset_attachments.(asset_id,asset_type) does not exist
and
AssetAttachment.where("(asset_id,asset_type) IN (?,?)",[[4,"Logo"],[1,"Image"]])
ActiveRecord::PreparedStatementInvalid: wrong number of bind variables (1 for 2) in: (asset_id,asset_type) IN (?,?)
Does anyone know how to do this? Thanks in advance

Answer 1

set vs. array
The core of the problem is: you are mixing sets and arrays in an impossible way.
elem IN (...) .. expects a set.
elem = ANY(...) .. expects an array.
You can use unnest() to transform an array to a set.
You can use the aggregate function array_agg() to transform a set to an array.
Errors
Here, you are trying to form an array from (asset_id, asset_type):
AssetAttachment.where([:asset_id, :asset_type] => [[4,"Logo"],[1,"Image"]])
.. which is impossible, since arrays have to consist of identical types, while we obviously deal with a numeric and a string constant (you kept the actual types a secret).
Here, you force "(asset_id, asset_type)" as single column name by double-quoting it:
AssetAttachment.where("(asset_id,asset_type)" => [[4,"Logo"],[1,"Image"]])
And finally, here you try provide a single bind variable for two ?:
AssetAttachment.where("(asset_id,asset_type) IN (?,?)",[[4,"Logo"],[1,"Image"]])
Valid SQL
In pure SQL, either of these work:
SELECT * FROM asset_attachments
WHERE (asset_id, asset_type) IN ((4, 'Logo'), (1, 'Image'));
SELECT * FROM asset_attachments
WHERE (asset_id, asset_type) IN (VALUES(4, 'Logo'), (1, 'Image'));
SELECT * FROM asset_attachments
WHERE (asset_id, asset_type) = ANY (ARRAY[(4, 'Logo'), (1, 'Image')]);
If you have a long list of possible matches, an explicit JOIN would prove faster:
SELECT *
FROM asset_attachments
JOIN (VALUES(4, 'Logo'), (1, 'Image')) AS v(asset_id, asset_type)
USING (asset_id, asset_type)
Valid syntax for AR
I am an expert with Postgres, with AR not so much. This simple form might work:
AssetAttachment.where("(asset_id,asset_type) IN ((?,?),(?,?))", 4,"Logo",1,"Image")
Not sure if this could work, not sure about single or double quotes either:
AssetAttachment.where((:asset_id, :asset_type) => [(4,'Logo'),(1,'Image')])