棉花糖：嵌套模式的词典

Question

我想知道如何序列化nest的字典Schema。

天真的，我希望像这样的语法能起作用：

fields.List(Schema)
fields.Dict(Schema)

或许

fields.List(fields.Nested(Schema))
fields.Dict(fields.Nested(Schema))

序列化的列表，Schema可以通过实现Nested(Schema, many=True)，但我不知道有关dict的Schema。

例如，假设我的对象是这样定义的：

from marshmallow import Schema, fields, pprint

class AlbumSchema(Schema):
    year = fields.Int()

class ArtistSchema(Schema):
    name = fields.Str()

    # What should I write, here?

    # This won't work
    albums = fields.Nested(AlbumSchema(), many=True)

    # If I write this, AlbumSchema is ignored, so this is equivalent to
    albums = fields.Dict(AlbumSchema(), many=True)
    # this, which is not satisfying (AlbumSchema unused)
    albums = fields.Dict()
    # This is not the way either
    albums = fields.Dict(fields.Nested(AlbumSchema))


album_1 = dict(year=1971)
album_2 = dict(year=1970)
bowie = dict(name='David Bowie',
             albums={
                 'Hunky Dory': album_1,
                 'The Man Who Sold the World': album_2
             }
        )

schema = ArtistSchema()
result = schema.dump(bowie)
pprint(result.data, indent=2)

我希望我的对象被序列化为

{ 'albums': { 'Hunky Dory': {'year': 1971},
              'The Man Who Sold the World': {'year': 1970}},
  'name': 'David Bowie'}

（问题也在GitHub上讨论了。）

Answer 1

目前无法实现，但这是一项功能请求：

• https://github.com/marshmallow-code/marshmallow/issues/483
• https://github.com/marshmallow-code/marshmallow/issues/496

并且已经进行了处理：

• https://github.com/marshmallow-code/marshmallow/compare/dev...deckar01:483-structured-dict

2017年12月31日：此功能已添加到棉花糖3.0.0b5（https://github.com/marshmallow-code/marshmallow/pull/700）中。