Interaction of --collectionSettersMode with --nullableReferenceAttributes

[strigefleur]

Using NR arg (--nullableReferenceAttributes) we can get collection decorated with attributes like that

  [XmlArray("ErrorList")]
  [XmlArrayItem("Error", Namespace = "http://ns-here")]
  public Collection<ErrorDataType> ErrorList
  {
    [return: MaybeNull] get => this._errorList;
    [param: AllowNull] init => this._errorList = value;
  }

though collection setters with backing field (--collectionSettersMode=Init) let init the collection

public ErrorListType()
{
    this._errorList = new Collection<ErrorDataType>();
}

Now there's a conflict, since removing the backing field entirely removes all of collection initializers - both nullable and not nullable, but letting it stay leads to erroneously initialized empty collections that supposed to be null.

Expected to have empty collection when empty tag presents (<ErrorList/>) but null collection when no tag presents.

Am I missing some obvious arg combination?

[mganss]

Can you provide a small example XSD and XML that shows the issue?

[strigefleur]

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<xs:schema xmlns="http://www.some-domain.com/resp"
                   elementFormDefault="qualified"
                   targetNamespace="http://www.some-domain.com/resp"
                   version="20250101"
                   xmlns:xs="http://www.w3.org/2001/XMLSchema">
	<xs:element name="SomeRespResp" type="SomeRespRespType"></xs:element>
	<xs:complexType name="SomeRespRespType">
		<xs:sequence>
			<xs:element minOccurs="0" name="ErrorList" type="ErrorListType"></xs:element>
		</xs:sequence>
	</xs:complexType>
	<xs:complexType name="ErrorListType">
		<xs:sequence>
			<xs:element name="Error" type="IntegrationSimpleErrorDataType" minOccurs="1" maxOccurs="unbounded">
			</xs:element>
		</xs:sequence>
	</xs:complexType>
	<xs:complexType name="IntegrationSimpleErrorDataType">
		<xs:sequence>
			<xs:element name="ErrorCode" type="xs:string" minOccurs="1" maxOccurs="1"></xs:element>
			<xs:element name="ErrorDesc" type="xs:string" minOccurs="0" maxOccurs="1"></xs:element>
		</xs:sequence>
	</xs:complexType>
</xs:schema>

<?xml version="1.0" encoding="utf-8"?>
<SomeRespResp xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                   xmlns:xsd="http://www.w3.org/2001/XMLSchema"
                   xmlns="http://www.some-domain.com/resp">
</SomeRespResp>

[mganss]

I think this has nothing to do with the accessor or nullability attributes. It seems XmlSerializer will always set the property ErrorList to an empty collection, regardless of whether there is an empty element or not. Setting IsNullable=true on XmlArrayAttribute (nillable="true" in the schema) doesn't make a difference either.

If you don't want the initialization to an empty collection in the generated class, use --collectionSettersMode=InitWithoutConstructorInitialization.

[mganss]

Found a way: use --ar-. This will not generate XmlArrayAttribute and XmlArrayItemAttribute and behave like you want.

[strigefleur]

Thank you for the idea.

Though I'm not quite sure this is the right way:

• --collectionSettersMode=Init is used to ensure consistency so that nobody could accidentally leave uninitiallized collection when creating the object (large schemas with lots of stuff we don't want to ever touch manually) and in the same time could not neither accidentally nor intentionally override existing collection when working with incoming object - so replacing it with InitWithoutConstructorInitialization would leave some place for possible mistakes;
• --ar- also drops init modifier along with the collection initializer and by doing so leads to same issue where one could just new() the object and leave it with wrongly null collection that is not nullable by schema.

[strigefleur]

I'd probably expect --nullableReferenceAttributes to be aware of --collectionSettersMode=Init so that when combined it would skip generating collection initializer for MayBeNull collections or something. Not sure it's nice enough as well.

[mganss]

Why not leave the collection setters mode as private? IMO this is the best way and consistent with .NET guidance.

• --ar- also drops init modifier along with the collection initializer and by doing so leads to same issue where one could just new() the object and leave it with wrongly null collection that is not nullable by schema.

I can't repro this. I still get init on the Error collection.

[strigefleur]

I can't repro this. I still get init on the Error collection.

There's full command we generate with (--ar- added lately trying the suggestion; v3.0.1188.0):

xscgen --netCore --compactTypeNames --collectionSettersMode=Init --nullable --nullableReferenceAttributes
--separateFiles --commandArgs- --output=$output --namespace=$namespace $_.FullName --integer=long
--ar-

so that without --ar- there's output

        public RespType()
        {
            this._errorList = new Collection<IntegrationSimpleErrorDataType>();
        }

        [XmlIgnoreAttribute()]
        [IgnoreMember]
        private Collection<IntegrationSimpleErrorDataType> _errorList;

        [AllowNullAttribute()]
        [MaybeNullAttribute()]
        [XmlArrayAttribute("ErrorList")]
        [XmlArrayItemAttribute("Error", Namespace="http://www.blabla/resp")]
        public Collection<IntegrationSimpleErrorDataType> ErrorList
        {
            get
            {
                return _errorList;
            }
            init
            {
                _errorList = value;
            }
        }

        [XmlIgnoreAttribute()]
        [IgnoreMember]
        public bool ErrorListSpecified
        {
            get
            {
                return ((this.ErrorList != null) 
                            && (this.ErrorList.Count != 0));
            }
        }

and with --ar- just

        [AllowNullAttribute()]
        [MaybeNullAttribute()]
        [XmlElementAttribute("ErrorList")]
        public ErrorListType ErrorList { get; set; }

notice how { get; init; } becomes { get; set; }.

Why not leave the collection setters mode as private? IMO this is the best way and consistent with .NET guidance.

I don't mind following any nice guidance, though it takes compromises here and there :)

[strigefleur]

Kinda weird, it looks like there's some arg conflict: both --collectionSettersMode=Init and --collectionSettersMode=Private make no sense when --ar- enabled.

Ah, well. It's no longer Collection<> so works as expected I guess.

[mganss]

When using --ar- the collection is in the ErrorListType and will have accessors as selected via --collectionSettersMode. IMO this should fully enable your use case.