Module: Sequel::Model::Associations

Included in:
Sequel::Model
Defined in:
lib/sequel_model/associations.rb,
lib/sequel_model/association_reflection.rb

Overview

Associations are used in order to specify relationships between model classes that reflect relations between tables in the database using foreign keys.

Each kind of association adds a number of methods to the model class which are specialized according to the association type and optional parameters given in the definition. Example:

class Project < Sequel::Model
  many_to_one :portfolio
  one_to_many :milestones
end

The project class now has the following instance methods:

  • portfolio - Returns the associated portfolio

  • portfolio=(obj) - Sets the associated portfolio to the object, but the change is not persisted until you save the record.

  • milestones - Returns an array of associated milestones

  • milestones_dataset - Returns a dataset that would return the associated milestones, allowing for further filtering/limiting/etc.

  • add_milestone(obj) - Associates the passed milestone with this object

  • remove_milestone(obj) - Removes the association with the passed milestone

  • remove_all_milestones - Removes associations with all associated milestones

If you want to override the behavior of the add_/remove_/remove_all_ methods, there are private instance methods created that a prepended with an underscore (e.g. _add_milestone). The private instance methods can be easily overridden, but you shouldn’t override the public instance methods, as they deal with how associations are cached.

By default the classes for the associations are inferred from the association name, so for example the Project#portfolio will return an instance of Portfolio, and Project#milestones will return an array of Milestone instances, in similar fashion to how ActiveRecord infers class names.

Association definitions are also reflected by the class, e.g.:

Project.associations
=> [:portfolio, :milestones]
Project.association_reflection(:portfolio)
=> {:type => :many_to_one, :name => :portfolio, :class_name => "Portfolio"}

Associations can be defined by either using the associate method, or by calling one of the three methods: many_to_one, one_to_many, many_to_many. Sequel::Model also provides aliases for these methods that conform to ActiveRecord conventions: belongs_to, has_many, has_and_belongs_to_many. For example, the following three statements are equivalent:

associate :one_to_many, :attributes
one_to_many :attributes
has_many :attributes

Defined Under Namespace

Modules: EagerLoading Classes: AssociationReflection

Instance Method Summary collapse

Instance Method Details

#all_association_reflections ⇒ Object

Array of all association reflections for this model class



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# File 'lib/sequel_model/associations.rb', line 53

def all_association_reflections
  association_reflections.values
end

#associate(type, name, opts = {}, &block) ⇒ Object

Associates a related model with the current model. The following types are supported:

  • :many_to_one - Foreign key in current model’s table points to associated model’s primary key. Each associated model object can be associated with more than one current model objects. Each current model object can be associated with only one associated model object. Similar to ActiveRecord/DataMapper’s belongs_to.

  • :one_to_many - Foreign key in associated model’s table points to this model’s primary key. Each current model object can be associated with more than one associated model objects. Each associated model object can be associated with only one current model object. Similar to ActiveRecord/DataMapper’s has_many.

  • :many_to_many - A join table is used that has a foreign key that points to this model’s primary key and a foreign key that points to the associated model’s primary key. Each current model object can be associated with many associated model objects, and each associated model object can be associated with many current model objects. Similar to ActiveRecord/DataMapper’s has_and_belongs_to_many.

A one to one relationship can be set up with a many_to_one association on the table with the foreign key, and a one_to_many association with the :one_to_one option specified on the table without the foreign key. The two associations will operate similarly, except that the many_to_one association setter doesn’t update the database until you call save manually.

The following options can be supplied:

  • *ALL types*:

    • :allow_eager - If set to false, you cannot load the association eagerly via eager or eager_graph

    • :class - The associated class or its name. If not given, uses the association’s name, which is camelized (and singularized unless the type is :many_to_one)

    • :eager - The associations to eagerly load when loading the associated object. For many_to_one associations, this is ignored unless this association is being eagerly loaded, as it doesn’t save queries unless multiple objects can be loaded at once.

    • :eager_block - If given, use the block instead of the default block when eagerly loading. To not use a block when eager loading (when one is used normally), set to nil.

    • :graph_conditions - The conditions to use on the SQL join when eagerly loading the association via eager_graph

    • :graph_join_type - The type of SQL join to use when eagerly loading the association via eager_graph

    • :graph_select - A column or array of columns to select from the associated table when eagerly loading the association via eager_graph. Defaults to all columns in the associated table.

    • :order - the column(s) by which to order the association dataset. Can be a singular column or an array.

    • :read_only - Do not add a setter method (for many_to_one or one_to_many with :one_to_one), or add_/remove_/remove_all_ methods (for one_to_many, many_to_many)

    • :reciprocal - the symbol name of the reciprocal association, if it exists. By default, sequel will try to determine it by looking at the associated model’s assocations for a association that matches the current association’s key(s). Set to nil to not use a reciprocal.

    • :select - the attributes to select. Defaults to the associated class’s table_name.*, which means it doesn’t include the attributes from the join table in a many_to_many association. If you want to include the join table attributes, you can use this option, but beware that the join table attributes can clash with attributes from the model table, so you should alias any attributes that have the same name in both the join table and the associated table.

  • :one_to_many, :many_to_many:

    • :limit - Limit the number of records to the provided value. Use an array with two arguments for the value to specify a limit and offset.

  • :many_to_one:

    • :key - foreign_key in current model’s table that references associated model’s primary key, as a symbol. Defaults to :“#name_id”.

  • :one_to_many:

    • :key - foreign key in associated model’s table that references current model’s primary key, as a symbol. Defaults to :“#Sequel::Model::Associations.selfself.nameself.name.underscore_id”.

    • :one_to_one: Create a getter and setter similar to those of many_to_one associations. The getter returns a singular matching record, or raises an error if multiple records match. The setter updates the record given and removes associations with all other records. When this option is used, the other association methods usually added are either removed or made private, so using this is similar to using many_to_one, in terms of the methods it adds, the main difference is that the foreign key is in the associated table instead of the current table.

  • :many_to_many:

    • :join_table - name of table that includes the foreign keys to both the current model and the associated model, as a symbol. Defaults to the name of current model and name of associated model, pluralized, underscored, sorted, and joined with ‘_’.

    • :left_key - foreign key in join table that points to current model’s primary key, as a symbol. Defaults to :“#Sequel::Model::Associations.selfself.nameself.name.underscore_id”.

    • :right_key - foreign key in join table that points to associated model’s primary key, as a symbol. Defaults to Defaults to :“#Sequel::Model::Associations.namename.to_sname.to_s.singularize_id”.

    • :graph_join_table_conditions - The conditions to use on the SQL join for the join table when eagerly loading the association via eager_graph

Raises:

  • (ArgumentError) 


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# File 'lib/sequel_model/associations.rb', line 147

def associate(type, name, opts = {}, &block)
  # check arguments
  raise ArgumentError unless [:many_to_one, :one_to_many, :many_to_many].include?(type) && Symbol === name

  # merge early so we don't modify opts
  opts = opts.merge(:type => type, :name => name, :block => block, :cache => true, :model => self)
  opts = AssociationReflection.new.merge!(opts)
  opts[:eager_block] = block unless opts.include?(:eager_block)
  opts[:graph_join_type] ||= :left_outer
  opts[:graph_conditions] = opts[:graph_conditions] ? opts[:graph_conditions].to_a : []
  opts[:graph_select] = Array(opts[:graph_select]) if opts[:graph_select]

  # find class
  case opts[:class]
    when String, Symbol
      # Delete :class to allow late binding
      opts[:class_name] ||= opts.delete(:class).to_s
    when Class
      opts[:class_name] ||= opts[:class].name
  end

  send(:"def_#{type}", name, opts)

  # don't add to association_reflections until we are sure there are no errors
  association_reflections[name] = opts
end

#association_reflection(name) ⇒ Object

The association reflection hash for the association of the given name.



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# File 'lib/sequel_model/associations.rb', line 175

def association_reflection(name)
  association_reflections[name]
end

#associations ⇒ Object

Array of association name symbols



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# File 'lib/sequel_model/associations.rb', line 180

def associations
  association_reflections.keys
end

#many_to_many(*args, &block) ⇒ Object Also known as: has_and_belongs_to_many

Shortcut for adding a many_to_many association, see associate



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# File 'lib/sequel_model/associations.rb', line 197

def many_to_many(*args, &block)
  associate(:many_to_many, *args, &block)
end

#many_to_one(*args, &block) ⇒ Object Also known as: belongs_to

Shortcut for adding a many_to_one association, see associate



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# File 'lib/sequel_model/associations.rb', line 191

def many_to_one(*args, &block)
  associate(:many_to_one, *args, &block)
end

#one_to_many(*args, &block) ⇒ Object Also known as: has_many

Shortcut for adding a one_to_many association, see associate



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# File 'lib/sequel_model/associations.rb', line 185

def one_to_many(*args, &block)
  associate(:one_to_many, *args, &block)
end