Remove Column#primary

It appears to have been used at some point in the past, but is no longer
used in any meaningful way. Whether a column is considered primary is
a property of the model, not the schema/column. This also removes the
need for yet another layer of caching of the model's schema, and we can
leave that to the schema cache.

activerecord/lib/active_record/attribute_methods.rb

@@ -455,7 +455,7 @@ module ActiveRecord
     end
 
     def pk_attribute?(name)
-      column_for_attribute(name).primary
+      name == self.class.primary_key
     end
 
     def typecasted_attribute_value(name)

activerecord/lib/active_record/connection_adapters/column.rb

@@ -14,7 +14,7 @@ module ActiveRecord
       end
 
       attr_reader :name, :default, :cast_type, :null, :sql_type, :default_function
-      attr_accessor :primary, :coder
+      attr_accessor :coder
 
       alias :encoded? :coder
 
@@ -36,7 +36,6 @@ module ActiveRecord
         @null             = null
         @default          = extract_default(default)
         @default_function = nil
-        @primary          = nil
         @coder            = nil
       end
 

activerecord/lib/active_record/model_schema.rb

@@ -219,16 +219,12 @@ module ActiveRecord
 
       # Returns an array of column objects for the table associated with this class.
       def columns
-        @columns ||= connection.schema_cache.columns(table_name).map do |col|
-          col = col.dup
-          col.primary = (col.name == primary_key)
-          col
-        end
+        connection.schema_cache.columns(table_name)
       end
 
       # Returns a hash of column objects for the table associated with this class.
       def columns_hash
-        @columns_hash ||= Hash[columns.map { |c| [c.name, c] }]
+        connection.schema_cache.columns_hash(table_name)
       end
 
       def column_types # :nodoc:
@@ -271,7 +267,7 @@ module ActiveRecord
       # Returns an array of column objects where the primary id, all columns ending in "_id" or "_count",
       # and columns used for single table inheritance have been removed.
       def content_columns
-        @content_columns ||= columns.reject { |c| c.primary || c.name =~ /(_id|_count)$/ || c.name == inheritance_column }
+        @content_columns ||= columns.reject { |c| c.name == primary_key || c.name =~ /(_id|_count)$/ || c.name == inheritance_column }
       end
 
       # Resets all the cached information about columns, which will cause them
@@ -308,8 +304,6 @@ module ActiveRecord
         @arel_engine             = nil
         @column_defaults         = nil
         @column_names            = nil
-        @columns                 = nil
-        @columns_hash            = nil
         @column_types            = nil
         @content_columns         = nil
         @dynamic_methods_hash    = nil

activerecord/test/cases/adapters/sqlite3/copy_table_test.rb

@@ -60,7 +60,6 @@ class CopyTableTest < ActiveRecord::TestCase
       assert_equal original_id.type, copied_id.type
       assert_equal original_id.sql_type, copied_id.sql_type
       assert_equal original_id.limit, copied_id.limit
-      assert_equal original_id.primary, copied_id.primary
     end
   end
 

activerecord/test/cases/base_test.rb

@@ -102,8 +102,8 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_columns_should_obey_set_primary_key
-    pk = Subscriber.columns.find { |x| x.name == 'nick' }
-    assert pk.primary, 'nick should be primary key'
+    pk = Subscriber.columns_hash[Subscriber.primary_key]
+    assert_equal 'nick', pk.name, 'nick should be primary key'
   end
 
   def test_primary_key_with_no_id

activerecord/test/cases/bind_parameter_test.rb

@@ -21,7 +21,7 @@ module ActiveRecord
       super
       @connection = ActiveRecord::Base.connection
       @subscriber   = LogListener.new
-      @pk         = Topic.columns.find { |c| c.primary }
+      @pk         = Topic.columns_hash[Topic.primary_key]
       @subscription = ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
     end
 
@@ -60,12 +60,10 @@ module ActiveRecord
       end
 
       def test_logs_bind_vars
-        pk = Topic.columns.find { |x| x.primary }
-
         payload = {
           :name  => 'SQL',
           :sql   => 'select * from topics where id = ?',
-          :binds => [[pk, 10]]
+          :binds => [[@pk, 10]]
         }
         event  = ActiveSupport::Notifications::Event.new(
           'foo',
@@ -87,7 +85,7 @@ module ActiveRecord
         }.new
 
         logger.sql event
-        assert_match([[pk.name, 10]].inspect, logger.debugs.first)
+        assert_match([[@pk.name, 10]].inspect, logger.debugs.first)
       end
     end
   end

activerecord/test/cases/primary_keys_test.rb

@@ -149,38 +149,6 @@ class PrimaryKeysTest < ActiveRecord::TestCase
     assert_equal k.connection.quote_column_name("foo"), k.quoted_primary_key
   end
 
-  def test_two_models_with_same_table_but_different_primary_key
-    k1 = Class.new(ActiveRecord::Base)
-    k1.table_name = 'posts'
-    k1.primary_key = 'id'
-
-    k2 = Class.new(ActiveRecord::Base)
-    k2.table_name = 'posts'
-    k2.primary_key = 'title'
-
-    assert k1.columns.find { |c| c.name == 'id' }.primary
-    assert !k1.columns.find { |c| c.name == 'title' }.primary
-    assert k1.columns_hash['id'].primary
-    assert !k1.columns_hash['title'].primary
-
-    assert !k2.columns.find { |c| c.name == 'id' }.primary
-    assert k2.columns.find { |c| c.name == 'title' }.primary
-    assert !k2.columns_hash['id'].primary
-    assert k2.columns_hash['title'].primary
-  end
-
-  def test_models_with_same_table_have_different_columns
-    k1 = Class.new(ActiveRecord::Base)
-    k1.table_name = 'posts'
-
-    k2 = Class.new(ActiveRecord::Base)
-    k2.table_name = 'posts'
-
-    k1.columns.zip(k2.columns).each do |col1, col2|
-      assert !col1.equal?(col2)
-    end
-  end
-
   def test_auto_detect_primary_key_from_schema
     MixedCaseMonkey.reset_primary_key
     assert_equal "monkeyID", MixedCaseMonkey.primary_key