Module | Sequel::Model::Associations::ClassMethods
In: | lib/sequel/model/associations.rb

Each kind of association adds a number of instance 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
        # or: many_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.
- portfolio_dataset - Returns a dataset that would return the associated portfolio, only useful in fairly specific circumstances.
- milestones - Returns an array of associated milestones
- 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.
- milestones_dataset - Returns a dataset that would return the associated milestones, allowing for further filtering/limiting/etc.

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 without calling super, as they deal with callbacks and caching.

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.

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"}

### Methods

all_association_reflections associate association_reflection associations eager_loading_dataset inherited many_to_many many_to_one one_to_many

### Attributes

association_reflections | [R] | All association reflections defined for this model (default: none).

### Public Instance methods

all_association_reflections()

Array of all association reflections for this model class

[Source]

         # File lib/sequel/model/associations.rb, line 420
    420:         def all_association_reflections
    421:           association_reflections.values
    422:         end

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

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.
- :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.
- :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.

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. Also, in most cases you need to specify the plural association name when using one_to_many with the :one_to_one option.

The following options can be supplied:

- *ALL types*:
  - :after_add - Symbol, Proc, or array of both/either specifying a callback to call after a new item is added to the association.
  - :after_load - Symbol, Proc, or array of both/either specifying a callback to call after the associated record(s) have been retrieved from the database. Not called when eager loading via eager_graph, but called when eager loading via eager.
  - :after_remove - Symbol, Proc, or array of both/either specifying a callback to call after an item is removed from the association.
  - :allow_eager - If set to false, you cannot load the association eagerly via eager or eager_graph
  - :before_add - Symbol, Proc, or array of both/either specifying a callback to call before a new item is added to the association.
  - :before_remove - Symbol, Proc, or array of both/either specifying a callback to call before an item is removed from the association.
  - :cartesian_product_number - he number of joins completed by this association that could cause more than one row for each row in the current table (default: 0 for many_to_one associations, 1 for *_to_many associations).
  - :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)
  - :clone - Merge the current options and block into the options and block used in defining the given association. Can be used to DRY up a bunch of similar associations that all share the same options such as :class and :key, while changing the order and block used.
  - :conditions - The conditions to use to filter the association, can be any argument passed to filter.
  - :dataset - A proc that is instance_evaled to get the base dataset to use for the _dataset method (before the other options are applied).
  - :distinct - Use the DISTINCT clause when selecting associating object, both when lazy loading and eager loading via .eager (but not when using .eager_graph).
  - :eager - The associations to eagerly load via eager when loading the associated object(s). 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.
  - :eager_graph - The associations to eagerly load via eager_graph when loading the associated object(s). 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_grapher - A proc to use to implement eager loading via eager graph, overriding the default. Takes three arguments, a dataset, an alias to use for the table to graph for this association, and the alias that was used for the current table (since you can cascade associations), Should return a copy of the dataset with the association graphed into it.
  - :eager_loader - A proc to use to implement eager loading, overriding the default. Takes three arguments, a key hash (used solely to enhance performance), an array of records, and a hash of dependent associations. The associated records should be queried from the database and the associations cache for each record should be populated for this to work correctly.
  - :extend - A module or array of modules to extend the dataset with.
  - :graph_block - The block to pass to join_table when eagerly loading the association via eager_graph.
  - :graph_conditions - The additional conditions to use on the SQL join when eagerly loading the association via eager_graph. Should be a hash or an array of all two pairs. If not specified, the :conditions option is used if it is a hash or array of all two pairs.
  - :graph_join_type - The type of SQL join to use when eagerly loading the association via eager_graph. Defaults to :left_outer.
  - :graph_only_conditions - The conditions to use on the SQL join when eagerly loading the association via eager_graph, instead of the default conditions specified by the foreign/primary keys. This option causes the :graph_conditions option to be ignored.
  - :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.
  - :limit - Limit the number of records to the provided value. Use an array with two arguments for the value to specify a limit and an offset.
  - :order - the column(s) by which to order the association dataset. Can be a singular column or an array.
  - :order_eager_graph - Whether to add the order to the dataset‘s order when graphing via eager graph. Defaults to true, so set to false to disable.
  - :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.* in a many_to_many association, which means it doesn‘t include the attributes from the join table. 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.
  - :validate - Set to false to not validate when implicitly saving any associated object.
- :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". Can use an array of symbols for a composite key association.
  - :primary_key - column in the associated table that :key option references, as a symbol. Defaults to the primary key of the associated table. Can use an array of symbols for a composite key association.
- :one_to_many:
  - :key - foreign key in associated model‘s table that references current model‘s primary key, as a symbol. Defaults to :"#{self.name.underscore}_id". Can use an array of symbols for a composite key association.
  - :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. Note that using this option still requires you to use a plural name when creating and using the association (e.g. for reflections, eager loading, etc.).
  - :primary_key - column in the current table that :key option references, as a symbol. Defaults to primary key of the current table. Can use an array of symbols for a composite key association.
- :many_to_many:
  - :graph_join_table_block - The block to pass to join_table for the join table when eagerly loading the association via eager_graph.
  - :graph_join_table_conditions - The additional conditions to use on the SQL join for the join table when eagerly loading the association via eager_graph. Should be a hash or an array of all two pairs.
  - :graph_join_table_join_type - The type of SQL join to use for the join table when eagerly loading the association via eager_graph. Defaults to the :graph_join_type option or :left_outer.
  - :graph_join_table_only_conditions - The conditions to use on the SQL join for the join table when eagerly loading the association via eager_graph, instead of the default conditions specified by the foreign/primary keys. This option causes the :graph_join_table_conditions option to be ignored.
  - :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 :"#{self.name.underscore}_id". Can use an array of symbols for a composite key association.
  - :left_primary_key - column in current table that :left_key points to, as a symbol. Defaults to primary key of current table. Can use an array of symbols for a composite key association.
  - :right_key - foreign key in join table that points to associated model‘s primary key, as a symbol. Defaults to Defaults to :"#{name.to_s.singularize}_id". Can use an array of symbols for a composite key association.
  - :right_primary_key - column in associated table that :right_key points to, as a symbol. Defaults to primary key of the associated table. Can use an array of symbols for a composite key association.
  - :uniq - Adds a after_load callback that makes the array of objects unique.

[Source]

         # File lib/sequel/model/associations.rb, line 585
    585:         def associate(type, name, opts = {}, &block)
    586:           raise(Error, 'invalid association type') unless assoc_class = ASSOCIATION_TYPES[type]
    587:           raise(Error, 'Model.associate name argument must be a symbol') unless Symbol === name
    588:
    589:           # merge early so we don't modify opts
    590:           orig_opts = opts.dup
    591:           orig_opts = association_reflection(opts[:clone])[:orig_opts].merge(orig_opts) if opts[:clone]
    592:           opts = orig_opts.merge(:type => type, :name => name, :cache => true, :model => self)
    593:           opts[:block] = block if block
    594:           opts = assoc_class.new.merge!(opts)
    595:           opts[:eager_block] = block unless opts.include?(:eager_block)
    596:           opts[:graph_join_type] ||= :left_outer
    597:           opts[:order_eager_graph] = true unless opts.include?(:order_eager_graph)
    598:           conds = opts[:conditions]
    599:           opts[:graph_conditions] = conds if !opts.include?(:graph_conditions) and Sequel.condition_specifier?(conds)
    600:           opts[:graph_conditions] = opts[:graph_conditions] ? opts[:graph_conditions].to_a : []
    601:           opts[:graph_select] = Array(opts[:graph_select]) if opts[:graph_select]
    602:           [:before_add, :before_remove, :after_add, :after_remove, :after_load, :extend].each do |cb_type|
    603:             opts[cb_type] = Array(opts[cb_type])
    604:           end
    605:
    606:           # find class
    607:           case opts[:class]
    608:             when String, Symbol
    609:               # Delete :class to allow late binding
    610:               opts[:class_name] ||= opts.delete(:class).to_s
    611:             when Class
    612:               opts[:class_name] ||= opts[:class].name
    613:           end
    614:           opts[:class_name] ||= ((self.name || '').split("::")[0..-2] + [camelize(opts.returns_array? ? singularize(name) : name)]).join('::')
    615:
    616:           send("def_#{type}""def_#{type}", opts)
    617:
    618:           orig_opts.delete(:clone)
    619:           orig_opts.merge!(:class_name=>opts[:class_name], :class=>opts[:class], :block=>block)
    620:           opts[:orig_opts] = orig_opts
    621:           # don't add to association_reflections until we are sure there are no errors
    622:           association_reflections[name] = opts
    623:         end

association_reflection(name)

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

[Source]

         # File lib/sequel/model/associations.rb, line 626
    626:         def association_reflection(name)
    627:           association_reflections[name]
    628:         end

associations()

Array of association name symbols

[Source]

         # File lib/sequel/model/associations.rb, line 631
    631:         def associations
    632:           association_reflections.keys
    633:         end

eager_loading_dataset(opts, ds, select, associations)

Modify and return eager loading dataset based on association options. Options:

[Source]

         # File lib/sequel/model/associations.rb, line 636
    636:         def eager_loading_dataset(opts, ds, select, associations)
    637:           ds = ds.select(*select) if select
    638:           if c = opts[:conditions]
    639:             ds = (c.is_a?(Array) && !Sequel.condition_specifier?(c)) ? ds.filter(*c) : ds.filter(c)
    640:           end
    641:           ds = ds.order(*opts[:order]) if opts[:order]
    642:           ds = ds.eager(opts[:eager]) if opts[:eager]
    643:           ds = ds.distinct if opts[:distinct]
    644:           if opts[:eager_graph]
    645:             ds = ds.eager_graph(opts[:eager_graph])
    646:             ds = ds.add_graph_aliases(opts.associated_key_alias=>[opts.associated_class.table_name, opts.associated_key_alias, SQL::QualifiedIdentifier.new(opts.associated_key_table, opts.associated_key_column)]) if opts.eager_loading_use_associated_key?
    647:           elsif opts.eager_loading_use_associated_key?
    648:             ds = if opts[:uses_left_composite_keys]
    649:               t = opts.associated_key_table
    650:               ds.select_more(*opts.associated_key_alias.zip(opts.associated_key_column).map{|a, c| SQL::AliasedExpression.new(SQL::QualifiedIdentifier.new(t, c), a)})
    651:             else
    652:               ds.select_more(SQL::AliasedExpression.new(SQL::QualifiedIdentifier.new(opts.associated_key_table, opts.associated_key_column), opts.associated_key_alias))
    653:             end
    654:           end
    655:           ds = ds.eager(associations) unless Array(associations).empty?
    656:           ds = opts[:eager_block].call(ds) if opts[:eager_block]
    657:           ds
    658:         end

inherited(subclass)

Copy the association reflections to the subclass

[Source]

         # File lib/sequel/model/associations.rb, line 661
    661:         def inherited(subclass)
    662:           super
    663:           subclass.instance_variable_set(:@association_reflections, @association_reflections.dup)
    664:         end

many_to_many(*args, &block)

Shortcut for adding a many_to_many association, see associate

[Source]

         # File lib/sequel/model/associations.rb, line 667
    667:         def many_to_many(*args, &block)
    668:           associate(:many_to_many, *args, &block)
    669:         end

many_to_one(*args, &block)

Shortcut for adding a many_to_one association, see associate

[Source]

         # File lib/sequel/model/associations.rb, line 672
    672:         def many_to_one(*args, &block)
    673:           associate(:many_to_one, *args, &block)
    674:         end

one_to_many(*args, &block)

Shortcut for adding a one_to_many association, see associate

[Source]

         # File lib/sequel/model/associations.rb, line 677
    677:         def one_to_many(*args, &block)
    678:           associate(:one_to_many, *args, &block)
    679:         end

[Validate]