# How to work with wildcard fields?

One of the xml schema traits is to support any extensions with wildcards.

    <xs:complexType name="MetadataType" mixed="false">
        <xs:sequence>
            <xs:any namespace="##any" minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:anyAttribute namespace="##other" processContents="lax"/>
    </xs:complexType>

The generator will roughly create this class for you.

    >>> from dataclasses import dataclass
    >>> from dataclasses import field
    >>> from typing import Dict
    >>> from typing import List
    ...
    >>> @dataclass
    ... class MetadataType:
    ...     any_element: List[object] = field(
    ...         default_factory=list,
    ...         metadata={
    ...              "type": "Wildcard",
    ...              "namespace": "##any",
    ...          }
    ...     )
    ...     other_attributes: Dict[str, str] = field(
    ...          default_factory=dict,
    ...          metadata={
    ...              "type": "Attributes",
    ...              "namespace": "##other",
    ...          }
    ...      )

xsdata comes with two generic models that are used during parsing and you can also use to generate any custom xml element.

Model | Description
--- | ---
`AnyElement` | Used to represent any xml structure, resembles a DOM Element
`DerivedElement` | Wrapper for type substitution elements eg <b xsi:type=”a”>…</b>

    >>> from xsdata.formats.dataclass.models.generics import AnyElement
    >>> from xsdata.formats.dataclass.models.generics import DerivedElement
    >>> from xsdata.formats.dataclass.serializers import XmlSerializer
    >>> from xsdata.formats.dataclass.serializers.config import SerializerConfig
    ...
    >>> obj = MetadataType(
    ...     any_element=[
    ...         AnyElement(
    ...             qname="bar",
    ...             children=[
    ...                 AnyElement(qname="first", text="1st", attributes={"a": "1"}),
    ...                 AnyElement(qname="second", text="2nd", attributes={"b": "2"}),
    ...                 DerivedElement(
    ...                     qname="third",
    ...                     value=MetadataType(other_attributes={"c": "3"})
    ...                 )
    ...             ]
    ...         )
    ...     ]
    ... )
    >>> config = SerializerConfig(pretty_print=True, xml_declaration=False)
    >>> serializer = XmlSerializer(config=config)
    >>> print(serializer.render(obj))
    <MetadataType>
      <bar>
        <first a="1">1st</first>
        <second b="2">2nd</second>
        <third xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" c="3" xsi:type="MetadataType"/>
      </bar>
    </MetadataType>