Last Update: 2011-07-16 11:31:03 -0700

Better model associations

The latest release of sequel_model includes a new associations functionality written by Jeremy Evans which replaces the old relations code in previous versions. Please note that this version is not completely backward-compatible and you should therefore upgrade with caution.

The new implementation supports three kinds of relations: one_to_many, many_to_one and many_to_many, which correspond to has_many, belongs_to and has_and_belongs_to_many relations in ActiveRecord. In fact, the new implementation includes aliases for ActiveRecord assocation macros and is basically compatible with ActiveRecord conventions. It also supports DRY implicit class name references. Here’s a simple example:

class Author < Sequel::Model
  has_many :books # equivalent to one_to_many

class Book < Sequel::Model
  belongs_to :author # equivalent to many_to_one
  has_and_belongs_to_many :categories # equivalent to many_to_many

class Category < Sequel::Model
  has_and_belongs_to_many :books

These macros will create the following methods:

  • Author#books, Author#add_book, Author#remove_book

  • Book#author, Book#categories, Book#add_category,


  • Category#books, Category#add_book, Category#remove_book

Unlike ActiveRecord, one_to_many and many_to_many association methods return a dataset:

a = Author[1234]
a.books.sql #=> 'SELECT * FROM books WHERE (author_id = 1234)'

You can also tell Sequel to cache the association result set and return it as an array:

class Author < Sequel::Model
  has_many :books, :cache => true

Author[1234].books.class #=> Array

You can of course bypass the defaults and specify class names and key names:

class Node < Sequel::Model
  belongs_to :parent, :class => Node
  belongs_to :session, :key => :producer_id

Another useful option is :order, which sets the order for the association dataset:

class Author < Sequel::Model
  has_many :books, :order => :title

Author[1234].books.sql #=> 'SELECT * FROM books WHERE (author_id =

1234) ORDER BY title’

More information about associations can be found in the Sequel documentation.

Other changes

  • Added configuration file for running specs (#186).

  • Changed Database#drop_index to accept fixed arity (#173).

  • Changed column definition sql to put UNSIGNED constraint before

unique in order to satisfy MySQL (#171).

  • Enhanced MySQL adapter to support load data local infile_, added

compress option for mysql connection by default (#172).

  • Fixed bug when inserting hashes in array tuples mode.

  • Changed SQLite adapter to catch RuntimeError raised when executing a

statement and raise Error::InvalidStatement with the offending SQL and error message (#188).

  • Fixed Dataset#reverse to not raise for unordered dataset (#189).

  • Added Dataset#unordered method and changed order to remove order if

nil is specified (#190).

  • Fixed reversing order of ASC expression (#164).

  • Added support for :null => true option when defining table columns


  • Fixed Symbol#method_missing to accept variable arity (#185).