Make the schema cache forward compatible with the changes in Column

Since rails#54333 The Column class added a new attribute `cast_type` that
might not be in the schema cache dump made by a Rails 8.0 application.

In that case, we should fallback to the previous behavior and fetch the
type from the connection.

Of course this is not ideal since it will still require a connection to
get the cast type, but for schema cache dumps made by Rails 8.1 we will
not need to connect to the database anymore.

This code can be removed after we release Rails 8.1.

Author: rafaelfranca

activerecord/lib/active_record/attributes.rb

@@ -241,8 +241,11 @@ def define_attribute(
 
       def _default_attributes # :nodoc:
         @default_attributes ||= begin
-          attributes_hash = columns_hash.transform_values do |column|
-            ActiveModel::Attribute.from_database(column.name, column.default, type_for_column(column))
+          # TODO: Remove the need for a connection after we release 8.1.
+          attributes_hash = with_connection do |connection|
+            columns_hash.transform_values do |column|
+              ActiveModel::Attribute.from_database(column.name, column.default, type_for_column(connection, column))
+            end
           end
 
           attribute_set = ActiveModel::AttributeSet.new(attributes_hash)
@@ -297,7 +300,8 @@ def resolve_type_name(name, **options)
           Type.lookup(name, **options, adapter: Type.adapter_name_from(self))
         end
 
-        def type_for_column(column)
+        def type_for_column(connection, column)
+          # TODO: Remove the need for a connection after we release 8.1.
           hook_attribute_type(column.name, super)
         end
     end

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

@@ -624,7 +624,8 @@ def build_fixture_sql(fixtures, table_name)
 
             columns.map do |name, column|
               if fixture.key?(name)
-                with_yaml_fallback(column.cast_type.serialize(fixture[name]))
+                # TODO: Remove fetch_cast_type and the need for connection after we release 8.1.
+                with_yaml_fallback(column.fetch_cast_type(self).serialize(fixture[name]))
               else
                 default_insert_value(column)
               end

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

@@ -146,7 +146,8 @@ def quote_default_expression(value, column) # :nodoc:
         if value.is_a?(Proc)
           value.call
         else
-          cast_type = column.respond_to?(:cast_type) ? column.cast_type : lookup_cast_type(column.sql_type)
+          # TODO: Remove fetch_cast_type and the need for connection after we release 8.1.
+          cast_type = column.respond_to?(:fetch_cast_type) ? column.fetch_cast_type(self) : lookup_cast_type(column.sql_type)
           value = cast_type.serialize(value)
           quote(value)
         end
@@ -209,6 +210,11 @@ def sanitize_as_sql_comment(value) # :nodoc:
         comment
       end
 
+      def lookup_cast_type(sql_type) # :nodoc:
+        # TODO: Make this method private after we release 8.1.
+        type_map.lookup(sql_type)
+      end
+
       private
         def type_casted_binds(binds)
           binds&.map do |value|
@@ -219,12 +225,6 @@ def type_casted_binds(binds)
             end
           end
         end
-
-        # In some adapters this executes queries; it should not be used in any
-        # hot paths. Instead prefer using `column.cast_type`.
-        def lookup_cast_type(sql_type)
-          type_map.lookup(sql_type)
-        end
     end
   end
 end

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

@@ -85,7 +85,8 @@ def schema_scale(column)
 
         def schema_default(column)
           return unless column.has_default?
-          type = column.cast_type
+          # TODO: Remove fetch_cast_type and the need for connection after we release 8.1.
+          type = column.fetch_cast_type(@connection)
           default = type.deserialize(column.default)
           if default.nil?
             schema_expression(column)

activerecord/lib/active_record/connection_adapters/column.rb

@@ -7,7 +7,7 @@ module ConnectionAdapters
     class Column
       include Deduplicable
 
-      attr_reader :name, :cast_type, :default, :sql_type_metadata, :null, :default_function, :collation, :comment
+      attr_reader :name, :default, :sql_type_metadata, :null, :default_function, :collation, :comment
 
       delegate :precision, :scale, :limit, :type, :sql_type, to: :sql_type_metadata, allow_nil: true
 
@@ -28,6 +28,11 @@ def initialize(name, cast_type, default, sql_type_metadata = nil, null = true, d
         @comment = comment
       end
 
+      def fetch_cast_type(connection) # :nodoc:
+        # TODO: Remove fetch_cast_type and the need for connection after we release 8.1.
+        @cast_type || connection.lookup_cast_type(sql_type)
+      end
+
       def has_default?
         !default.nil? || default_function
       end
@@ -105,6 +110,9 @@ def virtual?
         false
       end
 
+      protected
+        attr_reader :cast_type
+
       private
         def deduplicated
           @name = -name

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

@@ -160,7 +160,8 @@ def quote_default_expression(value, column) # :nodoc:
           elsif column.type == :uuid && value.is_a?(String) && value.include?("()")
             value # Does not quote function default values for UUID columns
           elsif column.respond_to?(:array?)
-            quote(column.cast_type.serialize(value))
+            # TODO: Remove fetch_cast_type and the need for connection after we release 8.1.
+            quote(column.fetch_cast_type(self).serialize(value))
           else
             super
           end
@@ -186,11 +187,12 @@ def type_cast(value) # :nodoc:
           end
         end
 
-        private
-          def lookup_cast_type(sql_type)
-            super(query_value("SELECT #{quote(sql_type)}::regtype::oid", "SCHEMA").to_i)
-          end
+        # TODO: Make this method private after we release 8.1.
+        def lookup_cast_type(sql_type) # :nodoc:
+          super(query_value("SELECT #{quote(sql_type)}::regtype::oid", "SCHEMA").to_i)
+        end
 
+        private
           def encode_array(array_data)
             encoder = array_data.encoder
             values = type_cast_array(array_data.values)

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

@@ -654,7 +654,8 @@ def copy_table(from, to, options = {})
                 column_options[:stored] = column.virtual_stored?
                 column_options[:type] = column.type
               elsif column.has_default?
-                default = column.cast_type.deserialize(column.default)
+                # TODO: Remove fetch_cast_type and the need for connection after we release 8.1.
+                default = column.fetch_cast_type(self).deserialize(column.default)
                 default = -> { column.default_function } if default.nil?
 
                 unless column.auto_increment?

activerecord/lib/active_record/model_schema.rb

@@ -619,8 +619,9 @@ def compute_table_name
           end
         end
 
-        def type_for_column(column)
-          type = column.cast_type
+        def type_for_column(connection, column)
+          # TODO: Remove the need for a connection after we release 8.1.
+          type = column.fetch_cast_type(connection)
 
           if immutable_strings_by_default && type.respond_to?(:to_immutable_string)
             type = type.to_immutable_string

activerecord/lib/active_record/type_caster/connection.rb

@@ -19,7 +19,8 @@ def type_for_attribute(attr_name)
         if schema_cache.data_source_exists?(table_name)
           column = schema_cache.columns_hash(table_name)[attr_name.to_s]
           if column
-            type = column.cast_type
+            # TODO: Remove fetch_cast_type and the need for connection after we release 8.1.
+            type = column.fetch_cast_type(@klass.lease_connection)
           end
         end
 

activerecord/test/assets/schema_dump_8_0.yml

@@ -0,0 +1,134 @@
+--- !ruby/object:ActiveRecord::ConnectionAdapters::SchemaCache
+columns:
+  colleges:
+  - &1 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    auto_increment: true
+    name: id
+    sql_type_metadata: &4 !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: INTEGER
+      type: :integer
+      limit:
+      precision:
+      scale:
+    'null': false
+    default:
+    default_function:
+    collation:
+    comment:
+  - &2 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    auto_increment:
+    name: name
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: varchar
+      type: :string
+      limit:
+      precision:
+      scale:
+    'null': false
+    default:
+    default_function:
+    collation:
+    comment:
+  courses:
+  - *1
+  - *2
+  - !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    auto_increment:
+    name: college_id
+    sql_type_metadata: *4
+    'null': true
+    default:
+    default_function:
+    collation:
+    comment:
+  courses_professors:
+  - !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    auto_increment:
+    name: course_id
+    sql_type_metadata: *4
+    'null': true
+    default:
+    default_function:
+    collation:
+    comment:
+  - !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    auto_increment:
+    name: professor_id
+    sql_type_metadata: *4
+    'null': true
+    default:
+    default_function:
+    collation:
+    comment:
+  dogs:
+  - *1
+  professors:
+  - *1
+  - *2
+primary_keys:
+  colleges: id
+  courses: id
+  courses_professors:
+  dogs: id
+  professors: id
+data_sources:
+  colleges: true
+  courses: true
+  courses_professors: true
+  dogs: true
+  professors: true
+indexes:
+  colleges: []
+  courses:
+  - !ruby/object:ActiveRecord::ConnectionAdapters::IndexDefinition
+    table: courses
+    name: index_courses_on_college_id
+    unique: false
+    columns:
+    - college_id
+    lengths: {}
+    orders: {}
+    opclasses: {}
+    where:
+    type:
+    using:
+    include:
+    nulls_not_distinct:
+    comment:
+    valid: true
+  courses_professors:
+  - !ruby/object:ActiveRecord::ConnectionAdapters::IndexDefinition
+    table: courses_professors
+    name: index_courses_professors_on_professor_id
+    unique: false
+    columns:
+    - professor_id
+    lengths: {}
+    orders: {}
+    opclasses: {}
+    where:
+    type:
+    using:
+    include:
+    nulls_not_distinct:
+    comment:
+    valid: true
+  - !ruby/object:ActiveRecord::ConnectionAdapters::IndexDefinition
+    table: courses_professors
+    name: index_courses_professors_on_course_id
+    unique: false
+    columns:
+    - course_id
+    lengths: {}
+    orders: {}
+    opclasses: {}
+    where:
+    type:
+    using:
+    include:
+    nulls_not_distinct:
+    comment:
+    valid: true
+  dogs: []
+  professors: []
+version: 0