The goal of this module is to move Adapter specific column definitions to the Adapter instead of having it in the schema dumper itself. This code represents the normal case. We can then redefine how certain data types may be handled in the schema dumper on the Adapter level by over-writing this code inside the database specific adapters

Methods
C
M
P
Instance Public methods
column_spec(column, types)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb, line 11
def column_spec(column, types)
  spec = prepare_column_options(column, types)
  (spec.keys - [:name, :type]).each{ |k| spec[k].insert(0, "#{k.to_s}: ")}
  spec
end
migration_keys()

Lists the valid migration options

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb, line 40
def migration_keys
  [:name, :limit, :precision, :scale, :default, :null]
end
prepare_column_options(column, types)

This can be overridden on a Adapter level basis to support other extended datatypes (Example: Adding an array option in the PostgreSQLAdapter)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb, line 20
def prepare_column_options(column, types)
  spec = {}
  spec[:name]      = column.name.inspect

  # AR has an optimization which handles zero-scale decimals as integers. This
  # code ensures that the dumper still dumps the column as a decimal.
  spec[:type]      = if column.type == :integer && /^(numeric|decimal)/ =~ column.sql_type
                       'decimal'
                     else
                       column.type.to_s
                     end
  spec[:limit]     = column.limit.inspect if column.limit != types[column.type][:limit] && spec[:type] != 'decimal'
  spec[:precision] = column.precision.inspect if column.precision
  spec[:scale]     = column.scale.inspect if column.scale
  spec[:null]      = 'false' unless column.null
  spec[:default]   = default_string(column.default) if column.has_default?
  spec
end