Define custom calculated fields #75
Description
Is your feature request related to a problem? Please describe.
DataModel schema should provide a way to define custom calculated fields even if these attributes are available while expanding associated entities e.g. A customer's order may have an orderEmail field that should be mapped with Person.email attribute.
Describe the solution you'd like
Field definition may have an attribute to define a custom @themost/query#QueryExpression and this query expression should be added in final view object e.g. CREATE VIEW OrderData AS SELECT OrderBase.id, OrderBase.ordererdDate, ..., PersonBase.email AS orderEmail FROM OrderBase LEFT JOIN PersonBase ON OrderBase.customer = PersonBase.id