Custom type mapping

When managing a big collection of models, it sometimes is tricky to split them into multiple python modules. Even more so if they depend on each other. For the models to be serializable by xsdata, they need to be able to import all other referenced models, which might not be possible due to circular imports.

One solution to get around this problem is to fence the imports within the python modules by using typing.TYPE_CHECKING and passing a dedicated type-map dictionary to the SerializerConfig.

city.py

from dataclasses import dataclass
from dataclasses import field
from typing import List
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from tests.models.typemapping.street import Street


@dataclass
class City:
    class Meta:
        global_type = False

    name: str
    streets: List["Street"] = field(default_factory=list)

street.py

from dataclasses import dataclass
from dataclasses import field
from typing import List
from typing import Optional
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from tests.models.typemapping.city import City
    from tests.models.typemapping.house import House


@dataclass
class Street:
    class Meta:
        global_type = False

    name: str
    city: Optional["City"] = None
    houses: List["House"] = field(default_factory=list)

house.py

from dataclasses import dataclass
from typing import Optional
from typing import TYPE_CHECKING

if TYPE_CHECKING:
    from tests.models.typemapping.street import Street


@dataclass
class House:
    class Meta:
        global_type = False

    number: int
    street: Optional["Street"] = None

By fencing the imports, we are able to keep our models in different python modules that are cleanly importable and considered valid by static type checkers.

Passing the type-map dictionary, which maps the class/model-names directly to imported objects, enables xsdata to serialize the models.

from xsdata.formats.dataclass.serializers import XmlSerializer
from xsdata.formats.dataclass.serializers.config import SerializerConfig

from tests.models.typemapping.city import City
from tests.models.typemapping.house import House
from tests.models.typemapping.street import Street


city1 = City(name="footown")
street1 = Street(name="foostreet")
house1 = House(number=23)
city1.streets.append(street1)
street1.houses.append(house1)

type_map = {"City": City, "Street": Street, "House": House}
serializer_config = SerializerConfig(pretty_print=True, globalns=type_map)

xml_serializer = XmlSerializer(config=serializer_config)
serialized_house = xml_serializer.render(city1)
print(serialized_house)

<?xml version="1.0" encoding="UTF-8"?>
<City>
  <name>footown</name>
  <streets>
    <name>foostreet</name>
    <houses>
      <number>23</number>
    </houses>
  </streets>
</City>