Fields

The dataclasses fields come with a useful metadata mapping that is provided as a third-party extension mechanism. This mechanism is used by xsdata to support advance xml features.

Metadata

`name`

The local name of the XML/JSON field.

>>> @dataclass
... class Root:
...     first: str = field(metadata={"name": "one"})
...     second: str = field(metadata={"name": "two"})
...
>>> root = Root(first="xml", second="json")
>>> print(serializer.render(root))
<Root>
  <one>xml</one>
  <two>json</two>
</Root>

Type: str

Default: The field name

`namespace`

The namespace name of the XML element or attribute.

>>> @dataclass
... class Root:
...     attr: str = field(metadata={"type": "Attribute", "namespace": "a"})
...     child: str = field(metadata={"type": "Element", "namespace": "c"})
...
>>> print(serializer.render(Root(attr="a", child="c")))
<Root xmlns:ns0="a" ns0:attr="a">
  <ns1:child xmlns:ns1="c">c</ns1:child>
</Root>

Type: str

Default: None

`nillable`

Specify if the field has to be present in the serialized result even when it doesn't have any meaningful content.

>>> @dataclass
... class Root:
...     first: Optional[str] = field(metadata={"nillable": True}, default=None)
...     second: Optional[str] = field(default=None)
...
>>> print(serializer.render(Root()))
<Root>
  <first xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
</Root>

Type: bool

Default: False

`sequence`

Fields will the same sequence number are rendered sequentially.

>>> @dataclass
... class Root:
...     a: List[int] = field(metadata={"sequence": 1})
...     b: int = field(metadata={"sequence": 1})
...     c: List[int] = field(metadata={"sequence": 1})
...
>>> root = Root(a=[1, 2, 3], b=4, c=[6, 7, 8])
>>> print(serializer.render(root))
<Root>
  <a>1</a>
  <b>4</b>
  <c>6</c>
  <a>2</a>
  <c>7</c>
  <a>3</a>
  <c>8</c>
</Root>

Type: int | None

Default: None

`tokens`

Specify if the field value is a whitespace concatenated sequence.

>>> @dataclass
... class Root:
...     child: List[int] = field(metadata={"type": "Element", "tokens": True})
...
>>> root = Root([1, 2, 3])
>>> print(serializer.render(root))
<Root>
  <child>1 2 3</child>
</Root>

Type: bool

Default: False

`format`

The field format option for types like datetime, or bytes.

>>> @dataclass
... class Root:
...     base16: bytes = field(metadata={"format": "base16"})
...     base64: bytes = field(metadata={"format": "base64"})
...     date: datetime.date = field(metadata=dict(format="%d/%m/%Y"))
...
>>> root = Root(
...     base16="xsdata".encode(),
...     base64="xsdata".encode(),
...     date=datetime.date(2024, 1, 15)
...  )
>>> print(serializer.render(root))
<Root>
  <base16>787364617461</base16>
  <base64>eHNkYXRh</base64>
  <date>15/01/2024</date>
</Root>

Type: str

Default: None

`type`

The type property allows to change how a field should behave during data binding.

Text

Represents a xml value node.

>>> @dataclass
... class Root:
...     value: str = field(metadata={"type": "Text"}, default="abc")
...
>>> print(serializer.render(Root()))
<Root>abc</Root>

Element

Represents a xml element node.

>>> @dataclass
... class Root:
...     value: str = field(metadata={"type": "Element"}, default="abc")
...
>>> print(serializer.render(Root()))
<Root>
  <value>abc</value>
</Root>

Attribute

Represents a xml attribute.

>>> @dataclass
... class Root:
...     value: str = field(metadata={"type": "Attribute"}, default="abc")
...
>>> print(serializer.render(Root()))
<Root value="abc"/>

Elements

Elements type represents repeatable choice elements. It's more commonly referred as Compound Fields.

>>> @dataclass
... class Root:
...     value: List[Union[str, int, bool]] = field(
...         metadata={
...             "type": "Elements",
...             "choices": (
...                 {"name": "string", "type": str},
...                 {"name": "integer", "type": int},
...                 {"name": "bool", "type": bool}
...             )
...         }
...     )
...
>>> root = Root(value=[1, True, "a", "b", True])
>>> print(serializer.render(root))
<Root>
  <integer>1</integer>
  <bool>true</bool>
  <string>a</string>
  <string>b</string>
  <bool>true</bool>
</Root>

Choice elements properties

Property	type	The real name of the element this choice represents.
name	str	The local name of the XML/JSON field.
type	str	The type hint.
nillable	bool	Specify if the choice has to be serialized when it has no content.
wildcard	bool	Wildcard element to match any xml string.
tokens	bool	Specify if the choice value is a whitespace concatenated sequence.
namespace	str	The namespace name of the XML element.
format	str	The value format for types like datetime, or bytes.
default	Any	Default value.
default_factory	Any	Default value factory.

Warning

A compound field can not contain ambiguous types because it's impossible to infer the element from the actual value.

The xml contenxt will raise an error. The solution is to introduce intermediate simple types or subclasses per element. This will resolve xml roundtrips but it will not work for certain json roundtrips.

Wildcard

This type represents xs:any elements or elements with type xs:AnyType.

This type optionally can have a list of acceptable choices similar to compound fields, otherwise during binding the parsers will try to find a suitable model automatically, if everything fails, the parser will use the generic AnyElement.

Wildcards can have a normal uri namespace or use one of xml schema generics.

##any: element from any namespace is allowed
##other: element from any namespace other than the parent’s namespace
##local: element must come from no namespace
##targetNamespace: element from the namespace of the parent can be present

>>> @dataclass
... class Root:
...     any: object = field(metadata={"type": "Wildcard"})
...
>>> xml = '<Root><child a="b">foo</child></Root>'
>>> parser.from_string(xml, clazz=Root)
Root(any=AnyElement(qname='child', text='foo', tail=None, children=[], attributes={'a': 'b'}))

Attributes

This type represents xs:anyAttribute elements and can practically absorb any attribute that it is not defined in the class, but it has to be defined as a dictionary.

Similar to Wildcard, this type can have a normal uri namespace or use one of xml schema generics.

##any: attributes from any namespace is allowed
##other: attributes from any namespace other than the parent’s namespace
##local: attributes must come from no namespace
##targetNamespace: attributes from the namespace of the parent can be present

>>> @dataclass
... class Root:
...     known: int = field(metadata={"type": "Attribute"})
...     attrs: dict = field(metadata={"type": "Attributes"})
...
>>> xml = '<Root known="1" unknown="2" />'
>>> xml = '<Root known="1" unknown="2" />'
>>> parser.from_string(xml, clazz=Root)
Root(known=1, attrs={'unknown': '2'})

Ignore

This type will force the binding context to ignore the field. Make sure your field is declared with init=False or with a default value otherwise data binding will fail.

>>> @dataclass
... class Root:
...     index: int = field(default_factory=int, metadata={"type": "Ignore"})
...
>>> print(serializer.render(Root()))
<Root/>

`wrapper`

The element name to wrap a single or a collection of elements or primitives, in order to avoid having a dedicated wrapper class.

>>> from dataclasses import dataclass, field
>>> from typing import List
>>>
>>> @dataclass
... class Library:
...     books: List[str] = field(
...         metadata={
...             "wrapper": "Books",
...             "name": "Title",
...             "type": "Element",
...         }
...     )
...
>>> obj = Library(
...     books = [
...         "python for beginners",
...         "beautiful xml",
...     ]
... )
>>>
>>> print(serializer.render(obj))
<Library>
  <Books>
    <Title>python for beginners</Title>
    <Title>beautiful xml</Title>
  </Books>
</Library>

Type: Optional[str]

Default: None

`mixed`

Specifies whether the field supports mixed content. The flag is indented for Wildcard types and indicates that the parser should attempt to grab any text/tail content from the xml element.

>>> @dataclass
... class Root:
...     content: object = field(metadata={"type": "Wildcard", "mixed": True})
...
>>> xml = '<Root><p>Paragraph</p> Tail</Root>'
>>> parser.from_string(xml, clazz=Root)
Root(content=[AnyElement(qname='p', text='Paragraph', tail=' Tail', children=[], attributes={})])

Type: bool

Default: False

`process_contents`

Specifies how Wildcard fields should behave, when they don't have a predefined list of choices. If strict is enabled, binding context will try to auto-locate a class that matches the qualified name, of the xml element, before trying using the AnyElement generic.

Type: strict | skip

Default: strict