tl;dr

query = Order.unscoped.where(uuid: uuids, id: ids)
Order.where(query.where_values.inject(:or))
#=> Order Load (0.7ms)  SELECT "orders".* FROM "orders" WHERE ("orders"."uuid" IN ('5459eed8350e1b472bfee48375034103', '21313213jkads', '43ujrefdk2384us') OR "orders"."id" IN (2, 3, 4))

---

Since the or method is not available in Rails 4, it's tricky to perform OR queries with arrays as arguments. Of course we can write raw SQL, but is there a simpler way to do it?

My coworker sent me a link to a discussion on ruby-forum.com. That's where we found the following code:

recipe_query = Recipe.where("pastry_id = 1").where("filling_id = 1")
Recipe.where(recipe_query.where_values.join(" OR "))

However, it didn't work. where_values returns an array of Arel::Nodes::In objects and we can't just join them.

There's a post on Stack Overflow where the author scoops into Arel methods.

Category.top_level.where_values.map(&:to_sql)
=> ["`categories`.`parent_id` IS NULL"]

Oh yeah, how could I forgot about to_sql? Strings in an array like this can be easily joined, so in our case the code looks as follows:

query = Order.where(uuid: uuids, id: ids)
Order.where(query.where_values.map(&:to_sql).join(" OR "))
#=> Order Load (0.7ms)  SELECT "orders".* FROM "orders" WHERE ("orders"."uuid" IN ('5459eed8350e1b472bfee48375034103', '21313213jkads', '43ujrefdk2384us') OR "orders"."id" IN (2, 3, 4))

That's it! Where values are now joined by or, not and.

But wait! We can do it better. Cameron Martin on StackOverflow posted a little more elegant version:

query = Order.where(uuid: uuids, id: ids)
Order.where(query.where_values.inject(:or))

Rails 4.1+

Rails 4.1 treats default_scope just as a regular scope. The default scope (if you have any) is included in the where_values result and inject(:or) will add or statement between the default scope and your wheres. That's bad.

To solve that, you just need to unscope the query.

query = Order.unscoped.where(uuid: uuids, id: ids)
Order.where(query.where_values.inject(:or))

---

Possible caveats

When performing a query, elements of the array are cast to corresponding types, so be careful.

ids = ["5459eed8350e1b472bfee48375034103", "2", "3"]
query = Order.where(uuid: ids, id: ids)
Order.where(query.where_values.map(&:to_sql).join(" OR "))
#=> Order Load (0.6ms)  SELECT "orders".* FROM "orders" WHERE ("orders"."uuid" IN ('5459eed8350e1b472bfee48375034103', '2', '3') OR "orders"."id" IN (5459, 2, 3))

Order.where(Order.arel_table[:uuid].in(ids).or(Order.arel_table[:id].in(ids)))

Order.where(Order[:uuid].in(ids).or(Order[:id].in(ids)))

NoMethodError: undefined method `[]' for #<Class:0x00000009741518>

scope :first_payment_between, -> (from, to) {
    joins(self.first_card_payment_between(from,to).values[:joins])
    .joins(self.first_direct_payment_between(from,to).values[:joins])
    .where(first_card_payment_between(from,to).ast.cores.last.wheres.inject{|ws, w| (ws &&= ws.and(w)) || w}
    .or(first_direct_payment_between(from,to).ast.cores.last.wheres.last))
  }