I am trying to update multiple rows. Some rows may have a value already. So if the value in that row was 2 and I wanted to update it with an additional 4 to make total of 6. How can I do that without querying each row for it's current value? Or must I do that?
I currently have something like thing like this.
item_match = Item.where("id IN (?)", item_match_ids).to_a
item_match.update_all(quantity: quantity)
If adding the same value to all records, you can use the following:
item_match.update_all("quantity = quantity + #{ quantity }")
This is much faster than updating the records individually. To be safe, you should make the quantity column non-null and set a default value. Be sure to sanitize the quantity value for SQL if it's user-supplied.
I think you must remove the to_a, leaving this way:
Item.where(id: [id1, id2, ...]).update_all(quantity: quantity)
But, if you want to add a quantity to each record you need use find each:
Item.where(id: [id1, id2, ...]).find_each do |item|
item.update(quantity: item.quantity + quantity)
end
You will find more of find_each here
