structured-facts-rgen.md

Structured Facts in RGen

User defines facts using RGen modeling. Since we place restrictions on what may be expressed we prescribe how this should be done.

The user writes the model.rb and places it like so:

{modulepath}
└── {module}
    └── lib
        |── augeas
        │   └── lenses
        ├── facter
            └── model.rb

This model requires a base class (that we write) called something like Facter::FacterModel. This model contains the base type Fact.

module MyModule::Facts < Facter::FacterModel

  class IpAddresses < Fact
    contains_many_uni 'devices', NetDevice
  end
  
  class NetDevice < Fact
    has_attr 'name', String
    has_attr 'ip', String
    has_attr 'mtu', Integer
  end

end

If the author of a fact want a more dynamic approach - say that users should be able to add their own keyed string data.

module MyModule::Facts < Facter::FacterModel

  class IpAddresses < Fact
    contains_many_uni 'devices', NetDevice
  end
  
  class NetDevice < Fact
    has_attr 'name', String
    has_attr 'ip', String
    contains_many_uni 'data', CustomData
  end

  class CustomData
    has_attr 'name', String
    has_attr 'value', String
  end
end

This is the simples way, we could naturally make the CustomData handle different data types, we could also make all Facts support this (all other facts inherit the ability).