Datamapper DataMapper

DM documentation says that we can place conditions on associations like so:

Article.all('author.name' => 'Michael')

Which works fine and dandy. However, if the association model does not have the property :name, it breaks with an 'unknown property name' error

ArgumentError: Unknown property 'name'
    from .../gems/gems/dm-core-0.9.11/lib/dm-core/query.rb:667:in `method_missing'
    from .../gems/gems/dm-core-0.9.11/lib/dm-core/associations/relationship.rb:110:in `get_children'

The problem lies in relationship.rb:

109            query.conditions.map! do |operator, property, bind_value|
110              if operator != :raw && child_key.has_property?(property.name)
111                bind_value = *children.map { |child| property.get(child) }.uniq
112              end
113              [ operator, property, bind_value ]
114            end

If we inspect the 'property' variable inside the loop when we are accessing the condition on the association model, the value is a DataMapper::Query::Path object, which does not have a 'name' attribute or method. In other words, DM thinks it's a property (as happens with regular queries) but instead it's getting a Query::Path.

A quick and dirty fix is a check:

108           query = collection.query.dup
109            query.conditions.map! do |operator, property, bind_value|
110              property = property.property if property.class == DataMapper::Query::Path
111              if operator != :raw && child_key.has_property?(property.name)
112                bind_value = *children.map { |child| property.get(child) }.uniq
113              end
114              [ operator, property, bind_value ]
115            end

But it's not the most elegant. As we can see, we need to substitute 'property' for 'property.property', since the Path object stores the property that we are putting the condition on. We see that this works when the association model has the property :name, only coincidentally, since Query::Path gets duck typed to act like a Property:

from query.rb

637      # duck type the DM::Query::Path to act like a DM::Property
638      def field(*args)
639        @property ? @property.field(*args) : nil
640      end