Pydantic

Pydantic override

We love using Pydantic , but we need have multiple overrides in place to enable specific functionality. This document tries to document these instances, as they are in essence exceptions to an otherwise well understood and documented architecture.

BaseModel __init__ override

We override de __init__ method to catch all validation errors and reissue them with an better error message.

FileModel override

We override both __new__ and __init__ of the FileModel to cache models from disk. The FileModel utilises the FileLoadContext to resolve relative paths and to retrieve models previously read as part of the loading of a root model.

Specifically we also use it to load a filepath from disk.

This mostly happens in validate, a Pydantic override, to make sure that if we initialize with a single unnamed argument (Pydantic only accepts keyword arguments) we try to parse it as a filepath.

ForcingBase, Structure and CrossSectionDefinition validate override

Validate is overriden to try to initialize the correct subclass of ForcingBase and CrossSectionDefinition, as discriminated unions do not work yet in Pydantic. I.e. if you specify Union{A, B} and A and B have clearly defined Literals it still can't choose whether to create A or B. The PR to fix this hasn't been merged yet.

The code is duplicated in three places.

INIBasedModel validate override

In INIBasedModel we override validate to make sure we can flatten any Section input coming from the parser.

Couldn't this be done in the parser?

Structure Root validator explicitely checks subclass

Because the validation behaviour is different for Compound, Dambreak etc. We might want to split these things once a new Pydantic release has been made that allows a root_validator to be overriden.