Default value from schema does not appear in produced data class

[Thomasb81]

Hello

test.xsd:

<xs:schema xmlns:ns="http://www.test.org" xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.test.org/" elementFormDefault="qualified">
	<xs:element name="root">
		<xs:complexType>
			<xs:sequence>
                            <xs:element name="property1" type="xs:boolean" default="false"/>
                            <xs:element name="property2" type="xs:boolean" minOccurs="0" default="false"/>
			</xs:sequence>
		</xs:complexType>
	</xs:element>
</xs:schema>

xsdata generate test.xsd

I got:

from dataclasses import dataclass, field
from typing import Optional

__NAMESPACE__ = "http://www.test.org/"


@dataclass
class Root:
    class Meta:
        name = "root"
        namespace = "http://www.test.org/"

    property1: bool = field(
        default=True,
        metadata={
            "type": "Element",
            "required": True,
        },
    )
    property2: Optional[bool] = field(
        default=None,
        metadata={
            "type": "Element",
        },
    )

The default value for property1 is present in the generated code but value for property2 has been replace by None.
This is done

xsdata/xsdata/codegen/handlers/sanitize_attributes_default_value.py

Lines 51 to 53 in 113322b

	if self.should_reset_default(attr):
	attr.fixed = False
	attr.default = None

I understand that we have incompatible concept, on one hand we have schema that can specify both an optional element and a default value and on an other hand we have https://peps.python.org/pep-0557/ which define field and default value, which is probably why currently the tool remove data previously read from schema.

For my application I would like to be able to retrieve the default value specified in the schema. The business logic will handle it, so I don't want to rely on defaulting mechanism from dataclasses. On the provided example, I would like to produce from a custom plugin where I can customize the rending following code :

@dataclass
class Root:
    class Meta:
        name = "root"
        namespace = "http://www.test.org/"

    property1: bool = field(
        metadata={
            "type": "Element",
            "required": True,
            "default": True,
        }
    )
    property2: bool = field(
        metadata={
            "type": "Element",
            "default": False,
        }
    )

The field default attribute is not anymore produce and the default value is produced in metadata dict.
Would you accept patch on sanitize_attributes_default_value.py to avoid losing default attribute value ?

Also I don't understand:

 attr.fixed = False 

[tefra]

<xs:element name="property2" type="xs:boolean" minOccurs="0" default="false"/>

Basically and optional element can't have a default value, let me run a few tests to see if we change the behavior it won't break the w3c test suite.

[tefra]

Basically we would have to generate this

    property2: None | bool = field(
        default=False,
        metadata={
            "type": "Element",
        },
    )

and let the parser deal with it if it's present with empty value use the default, if it's not present none, if it's present and the value is present parse.

[Thomasb81]

Hello

<xs:element name="property2" type="xs:boolean" minOccurs="0" default="false"/>

Basically and optional element can't have a default value, let me run a few tests to see if we change the behavior it won't break the w3c test suite.

I did not try your last enhancement at generating None | bool. I developed a plugin that basically replace the original jinja template. So I need to back port your change.

I try to use field default attribute by my own. But it has undesirable side effect for my application:

• I cannot anymore check if the field has effectively been set, since the field default mechanism is assigning the default value when the dataclass constructor is call.
• It will systematically generate element and attribute with the default value while the value has not been set during serialization.

So what you propose to generate is probably fine for most of the user and allow to demonstrate the capability to deal with default value.

But what I am interested as enhancement is to capture more xsd details, like default value if any with the type resolution. So I can make a custom use at my end in my plugin by putting the data into metadata dict.

[skinkie]

@tefra any update on this one? It would greatly help with the NeTEx schema as well which has optional attributes, but having the default greatly helps with finding missing references.

<xsd:attribute name="nameOfRefClass" type="NameOfClassAccessEquipmentRefStructureType" use="optional" default="LiftEquipment">

[nth-bailey]

Hey! In pyxsdata, we resolved this by preserving attr.schema_default when optional element defaults are sanitized to None, and exposing it directly in the dataclass field metadata as metadata={"default": <deserialized_value>}. This allows preserving and inspecting schema defaults even when fields are optional without forcing default values onto the dataclass instance.