# 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.