Pattern for Edge and Bus models

1. make a mutable struct using with_kw (for ease of parameter validation) for YourType
   • subtype either AbstractEdge or AbstractBus
   • any required fields should have no default
   • any optional fields should have default of missing
2. Define a constructor function build_{your_types} for your new edge or bus that takes a dict as the only argument
   • the dict is parsed from yaml or json file(s). For example, the build_loads function requires a :loads key in the dict
   • replace any missing fields that must be derived from user inputs (i.e. things needed in the power flow model)
     • for example, in a Load the reactive power can be derived using the q_to_p value
   • the constructor function must return a subtype of AbstractVector{YourType}
3. Ensure commptibilty with the MetaGraph
   • If you subtyped AbstractEdge make sure the AbstractVector{YourType} returned from your
   constructor is compatible with fill_edge_attributes!.
   • If you subtyped AbstractBus make sure the AbstractVector{YourType} returned from your
   constructor is compatible with fill_node_attributes!.

The fill_{edge,node}_attributes! methods are used in the Network builder to store all the attributes of YourType in the Network.graph. The Network.graph is used to build the power flow models – so you also will probably need to modify BranchFlowModel.jl to account for your new type. (But in the future we might be able to handle abstract edge or bus models that implement a certain set of attributes).

You might also want to extend the Network interface for your type. For example, when adding the Load type we added:

load_busses(net::AbstractNetwork) = (b for b in busses(net) if haskey(net[b], :Load))