Enable Deserialization of Many-to-One Nested Objects that DNE in DB
Enable Deserialization of Many-to-One Nested Objects that DNE in DB

Proposition: Given 'One' object composed of nested fields, with each
nested field containing 'Many' objects, on deserialization instantiate
each nested object into an instance of the nested field's SQLAlchemy
Model if it does not already exist in the DB.

Current behavior is to fail ungracefully & non-verbosely if a nested
object DNE in DB. The "NoResultFound" exception is raised by
"Query.one()".

The problem arises when sending a POST request to the server containing
a JSON object of a parent, with it's children nested inside as
a collection, and we try to deserialize this data with the intention
of INSERTing both the children, and the parent, and an EXC is raised.

marshmallow-code/marshmallow-sqlalchemy