[ruby-on-rails] Combine two ActiveRecord::Relation objects

Suppose I have the following two objects:

first_name_relation = User.where(:first_name => 'Tobias') # ActiveRecord::Relation
last_name_relation  = User.where(:last_name  => 'Fünke') # ActiveRecord::Relation

is it possible to combine the two relations to produce one ActiveRecord::Relation object containing both conditions?

Note: I'm aware that I can chain the wheres to get this behavior, what I'm really interested in is the case where I have two separate ActiveRecord::Relation objects.

I've been able to accomplish this, even in many odd situations, by using Rails' built-in Arel.

User.where(
  User.arel_table[:first_name].eq('Tobias').or(
    User.arel_table[:last_name].eq('Fünke')
  )
)

This merges both ActiveRecord relations by using Arel's or.

Merge, as was suggested here, didn't work for me. It dropped the 2nd set of relation objects from the results.

If you have an array of activerecord relations and want to merge them all, you can do

array.inject(:merge)

Brute force it:

first_name_relation = User.where(:first_name => 'Tobias') # ActiveRecord::Relation
last_name_relation  = User.where(:last_name  => 'Fünke') # ActiveRecord::Relation

all_name_relations = User.none
first_name_relation.each do |ar|
  all_name_relations.new(ar)
end
last_name_relation.each do |ar|
  all_name_relations.new(ar)
end

merge actually doesn't work like OR. It's simply intersection (AND)

I struggled with this problem to combine to ActiveRecord::Relation objects into one and I didn't found any working solution for me.

Instead of searching for right method creating an union from these two sets, I focused on algebra of sets. You can do it in different way using De Morgan's law

ActiveRecord provides merge method (AND) and also you can use not method or none_of (NOT).

search.where.none_of(search.where.not(id: ids_to_exclude).merge(search.where.not("title ILIKE ?", "%#{query}%")))

You have here (A u B)' = A' ^ B'

UPDATE: The solution above is good for more complex cases. In your case smth like that will be enough:

User.where('first_name LIKE ? OR last_name LIKE ?', 'Tobias', 'Fünke')

There is a gem called active_record_union that might be what you are looking for.

It's example usages is the following:

current_user.posts.union(Post.published)
current_user.posts.union(Post.published).where(id: [6, 7])
current_user.posts.union("published_at < ?", Time.now)
user_1.posts.union(user_2.posts).union(Post.published)
user_1.posts.union_all(user_2.posts)

This is how I've "handled" it if you use pluck to get an identifier for each of the records, join the arrays together and then finally do a query for those joined ids:

  transaction_ids = @club.type_a_trans.pluck(:id) + @club.type_b_transactions.pluck(:id) + @club.type_c_transactions.pluck(:id)
  @transactions = Transaction.where(id: transaction_ids).limit(100)

Relation objects can be converted to arrays. This negates being able to use any ActiveRecord methods on them afterwards, but I didn't need to. I did this:

name_relation = first_name_relation + last_name_relation

Ruby 1.9, rails 3.2