Models

Dataclasses is the default output format for the code generator and ships with its own modules for xml and json marshalling. The generated models are simple python dataclasses with some optional metadata to control how the data structures are transferred during data binding.

If you are working with xml documents that don’t have any schema definition you can create these models manually.

Basic Model

@dataclass
class Currency:
    id: int = field(metadata=dict(type="Attribute", name="ID"))
    name: str = field(metadata=dict(type="Attribute", name="Name"))
    num_code: int = field(metadata=dict(name="NumCode"))
    iso_code: str = field(metadata=dict(name="CharCode"))
    nominal: int = field(metadata=dict(name="Nominal"))
    value: Decimal = field(metadata=dict(name="Value"))


@dataclass
class Currencies:
    class Meta:
        name = "ValCurs"

    date: str = field(metadata=dict(type="Attribute", name="Date"))
    name: str = field(metadata=dict(type="Attribute"))
    values: List[Currency] = field(default_factory=list, metadata=dict(name="Valute"))

<ValCurs Date="19.04.2020" name="Official exchange rate">
    <Valute ID="47">
        <NumCode>978</NumCode>
        <CharCode>EUR</CharCode>
        <Nominal>1</Nominal>
        <Name>Euro</Name>
        <Value>19.2743</Value>
    </Valute>
    <Valute ID="44">
        <NumCode>840</NumCode>
        <CharCode>USD</CharCode>
        <Nominal>1</Nominal>
        <Name>US Dollar</Name>
        <Value>17.7177</Value>
    </Valute>
</ValCurs>

Class Meta

Property	Type	Description
name	str	The real name of the element this class represents.
nillable	bool	Specifies whether an explicit empty value can be assigned, default: False
namespace	str	The element xml namespace.

Field Typing

Simply follow the Python lib dataclasses documentation.

Field Metadata

Property	Type	Description
name	str	The real name of the element or attribute this field represents.
type	str	The field xml type: Text | Element | Elements | Attribute | Wildcard | Attributes, default: Text or Element
nillable	bool	Specifies whether an explicit empty value can be assigned.
mixed	bool	Specifies whether the field supports mixed content. (1)
sequential	bool	Specifies whether the field value(s) must appear in sequence with other sequential sibling fields. eg <a /><b /><a /><b />
tokens	bool	Use a list to map simple values. eg element: List[Union[int, bool, str]] -> <element>1 a true</element> -> [1, "a", True]
namespace	str	Specifies the field xml namespace. (2)

The code generator adds also the field restrictions like minLength or required flag but currently they are only used to troubleshoot the code generator.

1

Mixed content must be combined Wildcard fields with type List[object]. w3schools

2

It’s a common practice in schema definitions to require elements to be qualified and attributes to be unqualified.

Element fields with an omitted namespace inherit the namespace from the parent class/element and Attribute fields don’t.

If you need to break the namespace inheritance for Element fields set the namespace to an empty string namespace="".

Type: Element

This type represents a traditional xml element and can be the building block and container for other elements, attributes, text or any combination of them.

annotation: List[Annotation] = field(
    default_factory=list,
    metadata={
        "name": "annotation",
        "type": "Element",
        "namespace": "http://www.w3.org/XML/2004/xml-schema-test-suite/",
    )
)

 <annotation xmlns="http://www.w3.org/2001/XMLSchema">...</annotation>
 <annotation xmlns="http://www.w3.org/2001/XMLSchema">...</annotation>
 <annotation xmlns="http://www.w3.org/2001/XMLSchema">...</annotation>
...

Type: Elements

This type represents repeating xs:choice elements. It’s a compound list field for elements and wildcards that can be used to preserve elements ordering between data marshalling.

node_or_id_or_idref: List[object] = field(
    default_factory=list,
    metadata={
        "type": "Elements",
        "choices": (
            {
                "name": "node",
                "type": Type["Node"],
            },
            {
                "name": "e1",
                "type": str,
                "nillable": True,
            },
            {
                "name": "e2",
                "type": int,
                "namespace": "xsdata",
            },
        ),
    }
)

 <e1 xmlns="xsdata">a</e1>
 <e1 xmlns="xsdata">b</e1>
 <e2 xmlns="xsdata">1</e1>
 <e1 xmlns="xsdata">c</e1>
 <e2 xmlns="xsdata">2</e1>
...

Choice Metadata

Property	Type	Description
name	str	The real name of the element this choice represents.
type	str	The field type hint.
nillable	bool	Specifies whether an explicit empty value can be assigned.
wildcard	bool	Specifies whether this is a Wildcard that can match any tag.
tokens	bool	Use a list to map simple values. eg element: List[Union[int, bool, str]] -> <element>1 a true</element> -> [1, "a", True]
namespace	str	Specifies the field xml namespace.

Warning

Compound fields preserve elements ordering but instead the direct element name association is lost during marshalling. If the choices include multiple elements with the same type then it’s actually impossible to map correctly values to elements.

For that reason the xml parser will use the generic class DerivedElement to wrap values in order to maintain the original qualified name as well.

If your compound field includes only unique types and you are working with a dataclass instance manually you can skip the usage of the wrapper as the xml serializer will try to match a type to a choice as well.

obj.node_or_id_or_idref.extend(("a", "b", 1, "c", "2"))

Type: Attribute

This type represents a traditional xml attribute.

language: Optional[str] = field(
    default=None,
    metadata={
        "name": "lang",
        "type": "Attribute",
        "namespace": "http://www.w3.org/XML/1998/namespace"
    }
)

<root xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:lang="en">

Type: Wildcard

This type represents xs:any elements or elements with type xs:AnyType. Wildcards can have a normal uri namespace or use one of xml schema generics.

Namespace	Description
##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

any_element: List[object] = field(
    default_factory=list,
    metadata={
        "type": "Wildcard",
        "namespace": "##any",
    }
)

This type of field accepts any primitive value or an another dataclass instance or a generic AnyElement instance.

Type: Attributes

This type represents xs:anyAttribute elements. It needs to be defined as a dictionary of. The wildcard namespace features also apply.

any_attributes: Dict = field(
    default_factory=dict,
    metadata={
        "type": "Attributes",
        "namespace": "##other"
    }
)

Type: Text

This is the default field type and represents any atomic value. The value of this field is directly assigned as text to elements.

@dataclass
class Root:
    class Meta:
        name = "root"

    value: Optional[int] = field(default=None)

<root>2020</root>