Except `table_name` from column objects

The `table_name` was added at #23677 to detect whether serial column or
not correctly.

We can do that detection before initialize column object, it makes
column object size smaller, and it probably helps column object
de-duplication.

activerecord/lib/active_record/connection_adapters/column.rb

@@ -5,7 +5,7 @@ module ActiveRecord
   module ConnectionAdapters
     # An abstract definition of a column in a table.
     class Column
-      attr_reader :name, :default, :sql_type_metadata, :null, :table_name, :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
 
@@ -15,9 +15,8 @@ class Column
       # +default+ is the type-casted default value, such as +new+ in <tt>sales_stage varchar(20) default 'new'</tt>.
       # +sql_type_metadata+ is various information about the type of the column
       # +null+ determines if this column allows +NULL+ values.
-      def initialize(name, default, sql_type_metadata = nil, null = true, table_name = nil, default_function = nil, collation = nil, comment: nil, **)
+      def initialize(name, default, sql_type_metadata = nil, null = true, default_function = nil, collation: nil, comment: nil, **)
         @name = name.freeze
-        @table_name = table_name
         @sql_type_metadata = sql_type_metadata
         @null = null
         @default = default
@@ -44,7 +43,6 @@ def human_name
 
       def init_with(coder)
         @name = coder["name"]
-        @table_name = coder["table_name"]
         @sql_type_metadata = coder["sql_type_metadata"]
         @null = coder["null"]
         @default = coder["default"]
@@ -55,7 +53,6 @@ def init_with(coder)
 
       def encode_with(coder)
         coder["name"] = @name
-        coder["table_name"] = @table_name
         coder["sql_type_metadata"] = @sql_type_metadata
         coder["null"] = @null
         coder["default"] = @default
@@ -77,7 +74,7 @@ def hash
       protected
 
         def attributes_for_hash
-          [self.class, name, default, sql_type_metadata, null, table_name, default_function, collation]
+          [self.class, name, default, sql_type_metadata, null, default_function, collation, comment]
         end
     end
 

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

@@ -55,7 +55,7 @@ def schema_precision(column)
           end
 
           def schema_collation(column)
-            if column.collation && table_name = column.table_name
+            if column.collation
               @table_collation_cache ||= {}
               @table_collation_cache[table_name] ||=
                 @connection.exec_query("SHOW TABLE STATUS LIKE #{@connection.quote(table_name)}", "SCHEMA").first["Collation"]
@@ -65,13 +65,13 @@ def schema_collation(column)
 
           def extract_expression_for_virtual_column(column)
             if @connection.mariadb? && @connection.database_version < "10.2.5"
-              create_table_info = @connection.send(:create_table_info, column.table_name)
+              create_table_info = @connection.send(:create_table_info, table_name)
               column_name = @connection.quote_column_name(column.name)
               if %r/#{column_name} #{Regexp.quote(column.sql_type)}(?: COLLATE \w+)? AS \((?<expression>.+?)\) #{column.extra}/ =~ create_table_info
                 $~[:expression].inspect
               end
             else
-              scope = @connection.send(:quoted_scope, column.table_name)
+              scope = @connection.send(:quoted_scope, table_name)
               column_name = @connection.quote(column.name)
               sql = "SELECT generation_expression FROM information_schema.columns" \
                     " WHERE table_schema = #{scope[:schema]}" \

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

@@ -174,9 +174,8 @@ def new_column_from_field(table_name, field)
               default,
               type_metadata,
               field[:Null] == "YES",
-              table_name,
               default_function,
-              field[:Collation],
+              collation: field[:Collation],
               comment: field[:Comment].presence
             )
           end

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

@@ -2,42 +2,21 @@
 
 module ActiveRecord
   module ConnectionAdapters
-    # PostgreSQL-specific extensions to column definitions in a table.
-    class PostgreSQLColumn < Column #:nodoc:
-      delegate :array, :oid, :fmod, to: :sql_type_metadata
-      alias :array? :array
-
-      def initialize(*, max_identifier_length: 63, **)
-        super
-        @max_identifier_length = max_identifier_length
-      end
-
-      def serial?
-        return unless default_function
-
-        if %r{\Anextval\('"?(?<sequence_name>.+_(?<suffix>seq\d*))"?'::regclass\)\z} =~ default_function
-          sequence_name_from_parts(table_name, name, suffix) == sequence_name
+    module PostgreSQL
+      class Column < ConnectionAdapters::Column # :nodoc:
+        delegate :array, :oid, :fmod, to: :sql_type_metadata
+        alias :array? :array
+
+        def initialize(*, serial: nil, **)
+          super
+          @serial = serial
         end
-      end
 
-      private
-        attr_reader :max_identifier_length
-
-        def sequence_name_from_parts(table_name, column_name, suffix)
-          over_length = [table_name, column_name, suffix].map(&:length).sum + 2 - max_identifier_length
-
-          if over_length > 0
-            column_name_length = [(max_identifier_length - suffix.length - 2) / 2, column_name.length].min
-            over_length -= column_name.length - column_name_length
-            column_name = column_name[0, column_name_length - [over_length, 0].min]
-          end
-
-          if over_length > 0
-            table_name = table_name[0, table_name.length - over_length]
-          end
-
-          "#{table_name}_#{column_name}_#{suffix}"
+        def serial?
+          @serial
         end
+      end
     end
+    PostgreSQLColumn = PostgreSQL::Column # :nodoc:
   end
 end

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

@@ -650,16 +650,19 @@ def new_column_from_field(table_name, field)
             default_value = extract_value_from_default(default)
             default_function = extract_default_function(default_value, default)
 
-            PostgreSQLColumn.new(
+            if match = default_function&.match(/\Anextval\('"?(?<sequence_name>.+_(?<suffix>seq\d*))"?'::regclass\)\z/)
+              serial = sequence_name_from_parts(table_name, column_name, match[:suffix]) == match[:sequence_name]
+            end
+
+            PostgreSQL::Column.new(
               column_name,
               default_value,
               type_metadata,
               !notnull,
-              table_name,
               default_function,
-              collation,
+              collation: collation,
               comment: comment.presence,
-              max_identifier_length: max_identifier_length
+              serial: serial
             )
           end
 
@@ -675,6 +678,22 @@ def fetch_type_metadata(column_name, sql_type, oid, fmod)
             PostgreSQLTypeMetadata.new(simple_type, oid: oid, fmod: fmod)
           end
 
+          def sequence_name_from_parts(table_name, column_name, suffix)
+            over_length = [table_name, column_name, suffix].sum(&:length) + 2 - max_identifier_length
+
+            if over_length > 0
+              column_name_length = [(max_identifier_length - suffix.length - 2) / 2, column_name.length].min
+              over_length -= column_name.length - column_name_length
+              column_name = column_name[0, column_name_length - [over_length, 0].min]
+            end
+
+            if over_length > 0
+              table_name = table_name[0, table_name.length - over_length]
+            end
+
+            "#{table_name}_#{column_name}_#{suffix}"
+          end
+
           def extract_foreign_key_action(specifier)
             case specifier
             when "c"; :cascade

activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb

@@ -105,7 +105,7 @@ def new_column_from_field(table_name, field)
               end
 
             type_metadata = fetch_type_metadata(field["type"])
-            Column.new(field["name"], default, type_metadata, field["notnull"].to_i == 0, table_name, nil, field["collation"])
+            Column.new(field["name"], default, type_metadata, field["notnull"].to_i == 0, collation: field["collation"])
           end
 
           def data_source_sql(name = nil, type: nil)

activerecord/lib/active_record/schema_dumper.rb

@@ -47,6 +47,7 @@ def dump(stream)
     end
 
     private
+      attr_accessor :table_name
 
       def initialize(connection, options = {})
         @connection = connection
@@ -110,6 +111,8 @@ def tables(stream)
       def table(table, stream)
         columns = @connection.columns(table)
         begin
+          self.table_name = table
+
           tbl = StringIO.new
 
           # first dump primary key column
@@ -159,6 +162,8 @@ def table(table, stream)
           stream.puts "# Could not dump table #{table.inspect} because of following #{e.class}"
           stream.puts "#   #{e.message}"
           stream.puts
+        ensure
+          self.table_name = nil
         end
       end