1 files changed, 144 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
new file mode 100644
index 0000000000..6af5346fa7
--- /dev/null
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -0,0 +1,144 @@
+# frozen_string_literal: true
+
+require "set"
+
+module ActiveRecord
+  module AttributeMethods
+    module PrimaryKey
+      extend ActiveSupport::Concern
+
+      # Returns this record's primary key value wrapped in an array if one is
+      # available.
+      def to_key
+        key = id
+        [key] if key
+      end
+
+      # Returns the primary key column's value.
+      def id
+        sync_with_transaction_state
+        primary_key = self.class.primary_key
+        _read_attribute(primary_key) if primary_key
+      end
+
+      # Sets the primary key column's value.
+      def id=(value)
+        sync_with_transaction_state
+        primary_key = self.class.primary_key
+        _write_attribute(primary_key, value) if primary_key
+      end
+
+      # Queries the primary key column's value.
+      def id?
+        sync_with_transaction_state
+        query_attribute(self.class.primary_key)
+      end
+
+      # Returns the primary key column's value before type cast.
+      def id_before_type_cast
+        sync_with_transaction_state
+        read_attribute_before_type_cast(self.class.primary_key)
+      end
+
+      # Returns the primary key column's previous value.
+      def id_was
+        sync_with_transaction_state
+        attribute_was(self.class.primary_key)
+      end
+
+      # Returns the primary key column's value from the database.
+      def id_in_database
+        sync_with_transaction_state
+        attribute_in_database(self.class.primary_key)
+      end
+
+      private
+
+        def attribute_method?(attr_name)
+          attr_name == "id" || super
+        end
+
+        module ClassMethods
+          ID_ATTRIBUTE_METHODS = %w(id id= id? id_before_type_cast id_was id_in_database).to_set
+
+          def instance_method_already_implemented?(method_name)
+            super || primary_key && ID_ATTRIBUTE_METHODS.include?(method_name)
+          end
+
+          def dangerous_attribute_method?(method_name)
+            super && !ID_ATTRIBUTE_METHODS.include?(method_name)
+          end
+
+          # Defines the primary key field -- can be overridden in subclasses.
+          # Overwriting will negate any effect of the +primary_key_prefix_type+
+          # setting, though.
+          def primary_key
+            @primary_key = reset_primary_key unless defined? @primary_key
+            @primary_key
+          end
+
+          # Returns a quoted version of the primary key name, used to construct
+          # SQL statements.
+          def quoted_primary_key
+            @quoted_primary_key ||= connection.quote_column_name(primary_key)
+          end
+
+          def reset_primary_key #:nodoc:
+            if base_class?
+              self.primary_key = get_primary_key(base_class.name)
+            else
+              self.primary_key = base_class.primary_key
+            end
+          end
+
+          def get_primary_key(base_name) #:nodoc:
+            if base_name && primary_key_prefix_type == :table_name
+              base_name.foreign_key(false)
+            elsif base_name && primary_key_prefix_type == :table_name_with_underscore
+              base_name.foreign_key
+            else
+              if ActiveRecord::Base != self && table_exists?
+                pk = connection.schema_cache.primary_keys(table_name)
+                suppress_composite_primary_key(pk)
+              else
+                "id"
+              end
+            end
+          end
+
+          # Sets the name of the primary key column.
+          #
+          #   class Project < ActiveRecord::Base
+          #     self.primary_key = 'sysid'
+          #   end
+          #
+          # You can also define the #primary_key method yourself:
+          #
+          #   class Project < ActiveRecord::Base
+          #     def self.primary_key
+          #       'foo_' + super
+          #     end
+          #   end
+          #
+          #   Project.primary_key # => "foo_id"
+          def primary_key=(value)
+            @primary_key        = value && value.to_s
+            @quoted_primary_key = nil
+            @attributes_builder = nil
+          end
+
+          private
+
+            def suppress_composite_primary_key(pk)
+              return pk unless pk.is_a?(Array)
+
+              warn <<~WARNING
+                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
+end