diff options
| -rwxr-xr-x | activerecord/lib/active_record/associations.rb | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb index deadba7418..a82ea23b84 100755 --- a/activerecord/lib/active_record/associations.rb +++ b/activerecord/lib/active_record/associations.rb @@ -487,6 +487,22 @@ module ActiveRecord # When eager loaded, conditions are interpolated in the context of the model class, not the model instance. Conditions are lazily interpolated # before the actual model exists. # + # Eager loading is not possible with polymorphic associations. Given + # + # class Address < ActiveRecord::Base + # belongs_to :addressable, :polymorphic => true + # end + # + # a call that tries to eager load the addressable model + # + # Address.find(:all, :include => :addressable) # INVALID + # + # will raise <tt>ActiveRecord::EagerLoadPolymorphicError</tt>. The reason is that the parent model's type + # is a column value so its corresponding table name cannot be put in the FROM/JOIN clauses of that early query. + # + # It does work the other way around though: if the <tt>User</tt> model is <tt>addressable</tt> you can eager load + # their addresses with <tt>:include</tt> just fine, every piece needed to construct the query is known beforehand. + # # == Table Aliasing # # ActiveRecord uses table aliasing in the case that a table is referenced multiple times in a join. If a table is referenced only once, @@ -783,6 +799,7 @@ module ActiveRecord # a column name instead of a +true+/+false+ value to this option (e.g., <tt>:counter_cache => :my_custom_counter</tt>.) # Note: Specifying a counter_cache will add it to that model's list of readonly attributes using #attr_readonly. # * <tt>:include</tt> - specify second-order associations that should be eager loaded when this object is loaded. + # Not allowed if the association is polymorphic. # * <tt>:polymorphic</tt> - specify this association is a polymorphic association by passing +true+. # Note: If you've enabled the counter cache, then you may want to add the counter cache attribute # to the attr_readonly list in the associated classes (e.g. class Post; attr_readonly :comments_count; end). |