Move the warning about composite primary key to AttributeMethods::PrimaryKey

activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb

@@ -76,8 +76,10 @@ def self.retrieve_connection
           left_model.retrieve_connection
         end
 
-        def self.primary_key
-          false
+        private
+
+        def self.suppress_composite_primary_key(pk)
+          pk unless pk.is_a?(Array)
         end
       }
 

activerecord/lib/active_record/attribute_methods/primary_key.rb

@@ -95,7 +95,8 @@ def get_primary_key(base_name) #:nodoc:
             base_name.foreign_key
           else
             if ActiveRecord::Base != self && table_exists?
-              connection.schema_cache.primary_keys(table_name)
+              pk = connection.schema_cache.primary_keys(table_name)
+              suppress_composite_primary_key(pk)
             else
               'id'
             end
@@ -122,6 +123,18 @@ def primary_key=(value)
           @quoted_primary_key = nil
           @attributes_builder = nil
         end
+
+        private
+
+        def suppress_composite_primary_key(pk)
+          return pk unless pk.is_a?(Array)
+
+          warn <<-WARNING.strip_heredoc
+            WARNING: Active Record does not support composite primary key.
+
+            #{table_name} has composite primary key. Composite primary key is ignored.
+          WARNING
+        end
       end
     end
   end

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -129,14 +129,9 @@ def column_exists?(table_name, column_name, type = nil, options = {})
 
       # Returns just a table's primary key
       def primary_key(table_name)
-        pks = primary_keys(table_name)
-        warn <<-WARNING.strip_heredoc if pks.count > 1
-          WARNING: Rails does not support composite primary key.
-
-          #{table_name} has composite primary key. Composite primary key is ignored.
-        WARNING
-
-        pks.first if pks.one?
+        pk = primary_keys(table_name)
+        pk = pk.first unless pk.size > 1
+        pk
       end
 
       # Creates a new table with the name +table_name+. +table_name+ may either

activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb

@@ -124,6 +124,8 @@ def sql_for_insert(sql, pk, id_value, sequence_name, binds) # :nodoc:
             pk = primary_key(table_ref) if table_ref
           end
 
+          pk = suppress_composite_primary_key(pk)
+
           if pk && use_insert_returning?
             sql = "#{sql} RETURNING #{quote_column_name(pk)}"
           end
@@ -164,6 +166,12 @@ def commit_db_transaction
         def exec_rollback_db_transaction
           execute "ROLLBACK"
         end
+
+        private
+
+        def suppress_composite_primary_key(pk)
+          pk unless pk.is_a?(Array)
+        end
       end
     end
   end

activerecord/lib/active_record/schema_dumper.rb

@@ -105,12 +105,7 @@ def table(table, stream)
           tbl = StringIO.new
 
           # first dump primary key column
-          if @connection.respond_to?(:primary_keys)
-            pk = @connection.primary_keys(table)
-            pk = pk.first unless pk.size > 1
-          else
-            pk = @connection.primary_key(table)
-          end
+          pk = @connection.primary_key(table)
 
           tbl.print "  create_table #{remove_prefix_and_suffix(table).inspect}"
 

activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb

@@ -156,7 +156,7 @@ def test_join_table_composite_primary_key_should_not_warn
     warning = capture(:stderr) do
       country.treaties << treaty
     end
-    assert_no_match(/WARNING: Rails does not support composite primary key\./, warning)
+    assert_no_match(/WARNING: Active Record does not support composite primary key\./, warning)
   end
 
   def test_has_and_belongs_to_many

activerecord/test/cases/primary_keys_test.rb

@@ -255,6 +255,7 @@ class CompositePrimaryKeyTest < ActiveRecord::TestCase
 
   def setup
     @connection = ActiveRecord::Base.connection
+    @connection.schema_cache.clear!
     @connection.create_table(:barcodes, primary_key: ["region", "code"], force: true) do |t|
       t.string :region
       t.integer :code
@@ -270,10 +271,15 @@ def test_composite_primary_key
   end
 
   def test_primary_key_issues_warning
+    model = Class.new(ActiveRecord::Base) do
+      def self.table_name
+        "barcodes"
+      end
+    end
     warning = capture(:stderr) do
-      assert_nil @connection.primary_key("barcodes")
+      assert_nil model.primary_key
     end
-    assert_match(/WARNING: Rails does not support composite primary key\./, warning)
+    assert_match(/WARNING: Active Record does not support composite primary key\./, warning)
   end
 
   def test_collectly_dump_composite_primary_key