Add `ActiveRecord::Relation#extract_associated` for extracting associated record (#35784)

* Add `ActiveRecord::Relation#extract_associated` for extracting associated records from a relation

2 files changed, 14 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index 81ab502824..ae1501f5a1 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -13,7 +13,7 @@ module ActiveRecord
       :destroy_all, :delete_all, :update_all, :destroy_by, :delete_by,
       :find_each, :find_in_batches, :in_batches,
       :select, :reselect, :order, :reorder, :group, :limit, :offset, :joins, :left_joins, :left_outer_joins,
-      :where, :rewhere, :preload, :eager_load, :includes, :from, :lock, :readonly, :extending, :or,
+      :where, :rewhere, :preload, :extract_associated, :eager_load, :includes, :from, :lock, :readonly, :extending, :or,
       :having, :create_with, :distinct, :references, :none, :unscope, :optimizer_hints, :merge, :except, :only,
       :count, :average, :minimum, :maximum, :sum, :calculate, :annotate,
       :pluck, :pick, :ids
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 6f0f2125dc..c37855172b 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -154,6 +154,19 @@ module ActiveRecord
       self
     end
 
+    # Extracts a named +association+ from the relation. The named association is first preloaded,
+    # then the individual association records are collected from the relation. Like so:
+    #
+    #   account.memberships.extract_associated(:user)
+    #   # => Returns collection of User records
+    #
+    # This is short-hand for:
+    #
+    #   account.memberships.preload(:user).collect(&:user)
+    def extract_associated(association)
+      preload(association).collect(&association)
+    end
+
     # Use to indicate that the given +table_names+ are referenced by an SQL string,
     # and should therefore be JOINed in any query rather than loaded separately.
     # This method only works in conjunction with #includes.