eliminate warnings about multiple primary keys on habtm join tables

habtm join tables commonly have two id columns and it's OK to make those
two id columns a primary key.  This commit eliminates the warnings for
join tables that have this setup.

  ManageIQ/manageiq#6713

4 files changed, 18 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
index b888148841..5fbd79d118 100644
--- a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
+++ b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
@@ -76,6 +76,9 @@ module ActiveRecord::Associations::Builder # :nodoc:
           left_model.retrieve_connection
         end
 
+        def self.primary_key
+          false
+        end
       }
 
       join_model.name                = "HABTM_#{association_name.to_s.camelize}"
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
index 6aa264d766..6f2e03b370 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
@@ -118,7 +118,7 @@ module ActiveRecord
         alias :exec_update :exec_delete
 
         def sql_for_insert(sql, pk, id_value, sequence_name, binds) # :nodoc:
-          unless pk
+          if pk.nil?
             # Extract the table from the insert sql. Yuck.
             table_ref = extract_table_ref_from_insert_sql(sql)
             pk = primary_key(table_ref) if table_ref
diff --git a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
index 5c4586da19..bae4197aaf 100644
--- a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
@@ -146,6 +146,19 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     assert_equal 1, country.treaties.count
   end
 
+  def test_join_table_composit_primary_key_should_not_warn
+    country = Country.new(:name => 'India')
+    country.country_id = 'c1'
+    country.save!
+
+    treaty = Treaty.new(:name => 'peace')
+    treaty.treaty_id = 't1'
+    warning = capture(:stderr) do
+      country.treaties << treaty
+    end
+    assert_no_match(/WARNING: Rails does not support composite primary key\./, warning)
+  end
+
   def test_has_and_belongs_to_many
     david = Developer.find(1)
 
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index b9e0706d60..2a8996f35c 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -929,7 +929,7 @@ ActiveRecord::Schema.define do
     t.string :treaty_id
     t.string :name
   end
-  create_table :countries_treaties, force: true, id: false do |t|
+  create_table :countries_treaties, force: true, primary_key: [:country_id, :treaty_id] do |t|
     t.string :country_id, null: false
     t.string :treaty_id, null: false
   end