Tuesday, November 17, 2015

T4 Generates my business objects for me revisited with F#

A long time ago I wrote an article about the code I was using in T4 Generates my business objects for me. Today I've rewritten the idea with F# as the target. F# projects don't support T4 so I used a C# project to generate F# code into an F# project. The parts of the generated code
  • A readonly interface
  • A read-write interface
  • An F# record type
  • An F# module for mapping code methods (with Statically Resolved Type Parameter support aka Duck Typing or Structural Typing)
  • An F# class with INotifyPropertyChanged for WPF consumption
  • Implementing interfaces is not allowed to be implicit so I've automated that headache.
  • INotifyPropertyChanged desires magic strings (exception in the lovely new C# 6 nameof operator) so automation makes sure the strings are correct as of the last time T4 was run
  • If I pass around the read-only interface, I don't care how far down the rabbit hole of that object goes, it's immutable, no one is modifying it
  • If I pass around the read-write interface, all the consuming methods can be ignorant of concrete types
  • I'm generating Metadata from the db into the comments on the properties (tons of untapped potential here)

View the generated code and generator t4

- Generator and generated code from new T4 to F#

Things I want to add:

  • foreign key information to the auto-generated property comments
  • consider having the Read-Write interface implement the Read-Only interface
  • figure out how to update Microsoft's Type Providers to have them implement my interfaces.
  • add an option for generating Sql Sprocs that work against these types