Add AR::Base#load_async(*associations) as a nicer API

Author: byroot

activerecord/lib/active_record/associations.rb

@@ -324,6 +324,11 @@ def association(name) # :nodoc:
       association
     end
 
+    def load_async(*associations) # TODO: doc
+      associations.map { |name| association(name) }.each(&:async_load_target)
+      self
+    end
+
     def association_cached?(name) # :nodoc:
       @association_cache.key?(name)
     end

activerecord/lib/active_record/associations/association.rb

@@ -191,7 +191,7 @@ def async_load_target
         @target = find_target(async: true) if (@stale_state && stale_target?) || find_target?
 
         loaded! unless loaded?
-        @target
+        nil
       end
 
       # We can't dump @reflection and @through_reflection since it contains the scope proc
@@ -241,7 +241,7 @@ def find_target(async: false)
             if async
               return scope.load_async.then(&:to_a)
             else
-              return scope.to_a 
+              return scope.to_a
             end
           end
 

activerecord/test/cases/associations/belongs_to_associations_test.rb

@@ -1853,7 +1853,7 @@ def test_async_load_belongs_to
     client = Client.find(3)
     first_firm = companies(:first_firm)
 
-    promise = client.association(:firm).async_load_target
+    promise = client.load_async(:firm)
     wait_for_async_query
 
     events = []

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -3248,7 +3248,7 @@ class AsyncHasOneAssociationsTest < ActiveRecord::TestCase
   def test_async_load_has_many
     firm = companies(:first_firm)
 
-    promise = firm.association(:clients).async_load_target
+    promise = firm.load_async(:clients)
     wait_for_async_query
 
     events = []

activerecord/test/cases/associations/has_one_associations_test.rb

@@ -953,7 +953,7 @@ def test_async_load_has_one
     firm = companies(:first_firm)
     first_account = Account.find(1)
 
-    promise = firm.association(:account).async_load_target
+    promise = firm.load_async(:account)
     wait_for_async_query
 
     events = []