ActiveRecord has an .or method that allows you to create a query that matches one of multiple conditions.
Post.where(author: first_author).or(Post.where(author: second_author))
# SELECT `posts`.* FROM `posts` WHERE ((author_id = 1) OR (author_id = 2))
One gotcha is that the two relations must be structurally compatible. Most
commonly this means that the base relations must have the same .joins clauses,
but it applies to anything that isn’t a where clause or having clause.
This often leads to queries like this
Post
.joins(:category).where(categories: {name: "ruby"})
.or(Post.joins(:category).where(categories: {name: "rails"})
The joins(:category) bit must be repeated. This can feel a little verbose.
Enter .scoping! This method scopes all queries within the block to the current scope. We can use this to call our joins once, and within the block the relations are automatically scoped with the join.
Post.joins(:category).scoping do
Post.where(categories: {name: "ruby"})
.or(Post.where(categories: {name: "rails"})
end
If this is already in the Post class it’s even tidier!
joins(:category).scoping do
where(categories: {name: "ruby"}).or(where(categories: {name: "rails"}))
end
This has helped me make sense of more complex queries that join multiple associations and merge conditions from other models. Being able to extract the common structure makes it easier to see what conditions are being applied.
def self.in_progress
left_joins(:status, :delivery).scoping do
merge(OrderStatus.pending).or(merge(Delivery.active))
end
end
Happy scoping! 🤗
