module ActiveRecord::AttributeMethods::PrimaryKey::ClassMethods

def composite_primary_key? # :nodoc:

:nodoc: 
def composite_primary_key? # :nodoc:
  reset_primary_key if PRIMARY_KEY_NOT_SET.equal?(@primary_key)
  @composite_primary_key
end

def dangerous_attribute_method?(method_name) 

def dangerous_attribute_method?(method_name)
  super && !ID_ATTRIBUTE_METHODS.include?(method_name)
end

def get_primary_key(base_name) # :nodoc:

:nodoc: 
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
  elsif ActiveRecord::Base != self && table_exists?
    schema_cache.primary_keys(table_name)
  else
    "id"
  end
end

def inherited(base) 

def inherited(base)
  super
  base.class_eval do
    @primary_key = PRIMARY_KEY_NOT_SET
    @composite_primary_key = false
    @attributes_builder = nil
  end
end

def instance_method_already_implemented?(method_name) 

def instance_method_already_implemented?(method_name)
  super || primary_key && ID_ATTRIBUTE_METHODS.include?(method_name)
end

def primary_key

setting, though.
Overwriting will negate any effect of the +primary_key_prefix_type+
Defines the primary key field -- can be overridden in subclasses. 
def primary_key
  reset_primary_key if PRIMARY_KEY_NOT_SET.equal?(@primary_key)
  @primary_key
end

def primary_key=(value)

Project.primary_key # => "foo_id"

end
end
'foo_' + super
def self.primary_key
class Project < ActiveRecord::Base

You can also define the #primary_key method yourself:

end
self.primary_key = 'sysid'
class Project < ActiveRecord::Base

Sets the name of the primary key column. 
def primary_key=(value)
  @primary_key = if value.is_a?(Array)
    include CompositePrimaryKey
    @primary_key = value.map { |v| -v.to_s }.freeze
  elsif value
    -value.to_s
  end
  @composite_primary_key = value.is_a?(Array)
  @attributes_builder = nil
end

def quoted_primary_key

Returns a quoted version of the primary key name. 
def quoted_primary_key
  adapter_class.quote_column_name(primary_key)
end

def reset_primary_key # :nodoc:

:nodoc: 
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