Models Metadata¶

The code generator’s default output format is python dataclasses and ships with its own modules for xml and json marshalling.

The generated models don’t depend on the xsdata library, except for specific xsd data types that can’t be mapped directly to python’s builtin types. They only include some metadata properties in order to control how the data structures are transferred during data binding.

Basic Model¶

@dataclass
class Currency:
    id: int = field(metadata=dict(type="Attribute", name="ID"))
    name: str = field(metadata=dict(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"))


xml = """
<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>
"""

obj = XmlParser().from_string(xml, Currencies)
print(obj.values[1])

Currency(id=44, name='US Dollar', num_code=840, iso_code='USD', nominal=1, value=Decimal('17.7177'))

Class Metadata¶

Through the Meta class you can control the model’s behaviour during data binding procedures.

Property	Type	Description
name	str	The real/local name of the element this class represents.
nillable	bool	Specifies whether this class can be initialized with no values
namespace	str	The element xml namespace.
target_namespace	str	Specify the element target namespace for auto type locator, if module namespace is not available or the type is not qualified.
element_name_generator	Callable	Element name generator
attribute_name_generator	Callable	Attribute name generator

Field Typing¶

Simply follow the Python lib dataclasses documentation.

Warning

Currently only List, Tuple, Dict and Union annotations are supported. Everything else will raise an exception as unsupported.

Field Metadata¶

Through the metadata properties you can control the field’s behaviour during data binding procedures.

Property	Type	Description
name	str	The real/local name of the element or attribute this field represents.
type	str	The field xml type: `Ignore \| Text \| Element \| Elements \| Attribute \| Wildcard \| Attributes`, default: `Text` or `Element`
nillable	bool	Specifies whether an explicit `None` value is allowed, default: False
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	Map the field value to a python sequence, 2
namespace	str	Specifies the field xml namespace. 3
format	str	Format option for types like datetime, or bytes, see Data Types

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

Declaration: List[Union[int, bool, str]]

Serialized value: <element>1 a true</element>

Parsed value: [1, "a", True]

3

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: Ignore¶

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

index: int = field(
    default_factory=int,
    init=False,
    metadata={"type": "Ignore"},
)

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	Map the field value to a python sequence
namespace	str	Specifies the field xml namespace.
format	str	Format option for types like datetime, or bytes, see Data Types
default	Any	Default value
default_factory	Any	Default value factory

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",
        "choices": (
            {
                "name": "DSAKeyValue",
                "type": DsakeyValue,
                "namespace": "http://www.w3.org/2000/09/xmldsig#",
            },
            {
                "name": "RSAKeyValue",
                "type": RsakeyValue,
                "namespace": "http://www.w3.org/2000/09/xmldsig#",
            },
        ),
    }
)

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

This type optionally can have a list of acceptable elements similar to compound fields, otherwise during binding the parsers will try to find a suitable model automatically.

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>

Hint

Check the examples for more advanced topics.