Add :extend association option, for extending a dataset with module(s)

Update the advanced_associations.rdoc file to show a cool usage of
this.

sequel/CHANGELOG

@@ -1,5 +1,9 @@
 === HEAD
 
+* Add :extend association option, extending the dataset with module(s) (jeremyevans)
+
+* Add :after_load association callback option, called after associated objects have been loaded from the database (jeremyevans)
+
 * Make validation methods support a :tag option, to work correctly with source reloading (jeremyevans)
 
 * Add :before_add, :after_add, :before_remove, :after_remove association callback options (jeremyevans)

sequel/doc/advanced_associations.rdoc

@@ -151,9 +151,22 @@ otherwise modified:
     one_to_many :authorships
   end
   Author.first.authorships_dataset.filter(:number < 10).first
-
-If you want to add methods to the association instead of just using existing
-methods:
+
+You can extend a dataset with a module easily with :extend:
+
+  module FindOrCreate
+    def find_or_create(vals)
+      first(vals) || @opts[:models][nil].create(vals)
+    end
+  end
+  class Author < Sequel::Model
+    one_to_many :authorships, :extend=>FindOrCreate
+  end
+  Author.first.authorships_dataset.find_or_create(:name=>'Blah', :number=>10)
+
+However, note that the dataset doesn't have any knowledge of the model object
+that created it via the association, so if you want to use attributes of the
+model object, you'll have to use a closure:
 
   class Author < Sequel::Model
     one_to_many :authorships, :dataset=>(proc do
@@ -167,6 +180,18 @@ methods:
   end
   Author.first.authorships_dataset.find_or_create_by_name('Bob')
 
+You can cheat if you want to:
+
+  module FindOrCreate
+    def find_or_create(vals)
+      # Exploits the fact that Sequel filters are ruby objects that
+      # can be introspected.
+      author_id = @opts[:where].args[1]
+      first(vals) || \
+        @opts[:models][nil].create(vals.merge(:author_id=>author_id))
+    end 
+  end
+
 ===has_many :through associations
 
 many_to_many handles the usual case of a has_many :through with a belongs_to in

sequel/lib/sequel_model/associations.rb

@@ -118,6 +118,7 @@ def all_association_reflections
   #     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
@@ -193,7 +194,7 @@ def associate(type, name, opts = {}, &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]
-    [:before_add, :before_remove, :after_add, :after_remove, :after_load].each do |cb_type|
+    [:before_add, :before_remove, :after_add, :after_remove, :after_load, :extend].each do |cb_type|
       opts[cb_type] = Array(opts[cb_type])
     end
 
@@ -333,6 +334,7 @@ def def_association_dataset_methods(opts)
     eager = opts[:eager]
     eager_graph = opts[:eager_graph]
     limit = opts[:limit]
+    exten = opts[:extend]
     single = opts[:type] == :many_to_one
     key = opts[:key] if opts[:type] == :many_to_one
     set_reciprocal = opts[:type] == :one_to_many
@@ -348,6 +350,7 @@ def def_association_dataset_methods(opts)
     class_def(dataset_method) do
       raise(Sequel::Error, 'model object does not have a primary key') unless pk || single
       ds = instance_eval(&dataset)
+      exten.each{|m| ds.extend(m)}
       ds = ds.select(*opts.select) if opts.select
       ds = ds.order(*order) if order
       ds = ds.limit(*limit) if limit

sequel/spec/associations_spec.rb

@@ -15,6 +15,32 @@ class ParParent < Sequel::Model
     klass.association_reflection(:"par_parent1s").associated_class.should == ParParent
     klass.association_reflection(:"par_parent2s").associated_class.should == ParParent
   end
+  it "should allow extending the dataset with :extend option" do
+    MODEL_DB.reset
+    klass = Class.new(Sequel::Model(:nodes)) do
+      columns :id, :a_id
+    end
+    mod = Module.new do
+      def blah
+       1
+      end
+    end
+    mod2 = Module.new do
+      def blar
+       2
+      end
+    end
+
+    klass.associate :many_to_one, :a, :class=>klass, :extend=>mod
+    klass.associate :one_to_many, :bs, :class=>klass, :extend=>[mod]
+    klass.associate :many_to_many, :cs, :class=>klass, :extend=>[mod, mod2]
+
+    node = klass.load(:id=>1)
+    node.a_dataset.blah.should == 1
+    node.bs_dataset.blah.should == 1
+    node.cs_dataset.blah.should == 1
+    node.cs_dataset.blar.should == 2
+  end
 end
 
 describe Sequel::Model, "many_to_one" do