Esengine need to provide a a way to manage derived fields created in querys.

[ederfmartins]

When we add a field to a document inside a query, we need a way to use this field in our document model. Any ideias @rochacbruno, @andryw?

• Use a anotation to emulate derived script_fields as properties.
• Create a ScriptField that is a field derived from a script_field query
• Create a ViewDoc that represent a view of the doctype on index
  Questions:
• How to manage null values generated by a query that select few document fields?

[andryw]

I like the ScriptField solution.
Another solution could be create a intern field "ScriptField" on Document. When the user pass scriptfields on a query, this field (a dict) is filled. This solution is good because it doesn't need to modify the model to create a ScriptField. Sometimes the new field is temporary and it isn't necessary to modify the model for a temporary field. Besides the model could be on a project that you don't have permission to modify.

We will implement both solution and make pull request.