I have the following Python class and Marshmallow schema definitions:
from marshmallow import Schema, fields, post_load
class Author:
def __init__(self, id, name):
self.id = id
self.name = name
class Book:
def __init__(self, id, author, name):
self.id = id
assert isinstance(author, Author)
self.author = author
self.name = name
class Library:
def __init__(self, authors, books):
self.authors = authors
self.books = books
class AuthorSchema(Schema):
id = fields.Int()
name = fields.Str()
@post_load
def make_obj(self, data):
return Author(**data)
class BookSchema(Schema):
id = fields.Int()
author_id = fields.Method('get_id', 'get_author', attribute="author")
name = fields.Str()
@post_load
def make_obj(self, data):
return Book(**data)
def get_id(self, obj):
return obj.author.id
def get_author(self, value):
return [a for a in authors if a.id == value][0]
class LibrarySchema(Schema):
authors = fields.List(fields.Nested(AuthorSchema()))
books = fields.List(fields.Nested(BookSchema()))
@post_load
def make_obj(self, data):
return Library(**data)
# preserve ordering of fields
class Meta:
ordered = True
def test_author_referencing():
author1 = Author(1, "Astrid Lindgren")
author2 = Author(2, "Tove Jansson")
book1 = Book(11, author1, "The Brothers Lionheart")
book2 = Book(12, author2, "Comet in Moominland")
library = Library(authors=[author1, author2], books=[book1, book2])
schema = LibrarySchema(strict=True)
library_dict = schema.dump(library).data
library2 = schema.load(library_dict).data
As the sample hopefully illustrates, I'd like to have a data model in which book objects contain references to authors (instead of just author ids), but which would be serialized into author ids.
Obviously, serializing is not a problem, but when deserializing,
I'd need to access the already deserialized contents of the authors list. I can't quite figure how to do that with Marshmallow. Is it even possible? Of course, in this case I could instantiate Book objects with numeric author ids and do a @post_load operation in LibrarySchema to replace the author id with a reference, but that feels dirty and clunky to me. Please help. :-)
