Nullable enum properties missing minOccurs="0" in generated WSDL

[suntereo]

Nullable enum properties missing minOccurs="0" in generated WSDL

Description

Nullable enum properties in DataContract classes are not generating minOccurs="0" in the WSDL, causing them to be incorrectly marked as required. This affects client proxy generation, where these properties are generated with IsRequired=true even when explicitly configured otherwise.

String properties work correctly (include minOccurs="0"), but enum properties do not, regardless of:

• Using nullable syntax (Nullable<T> or T?)
• Setting [DataMember(IsRequired = false)]
• Setting [DataMember(EmitDefaultValue = false)]
• Combining both attributes

Environment

• SoapCore Version: 1.2.1.11
• .NET Version: 8.0
• OS: Windows (reproduced on multiple systems)

Expected Behavior

Nullable enum properties should render in the WSDL with minOccurs="0", similar to how string properties behave:

<xs:element minOccurs="0" name="NullableEnumProperty" nillable="true" type="tns:WorkflowState"/>

Actual Behavior

Nullable enum properties only get nillable="true" but are missing minOccurs="0":

<xs:element nillable="true" type="tns:WorkflowState" name="NullableEnumProperty"/>

This causes the element to be required but nullable, rather than optional.

Real-World Impact

When clients generate proxies using svcutil or Visual Studio's "Add Service Reference":

• All nullable enum properties are generated with [DataMember(IsRequired=true)]
• Clients must include these fields in every request, even when they should be optional
• This breaks scenarios where enum values should truly be optional

Reproduction Code

TestService.cs:

using System.Runtime.Serialization;
using System.ServiceModel;

namespace SoapCoreEnumIssue
{
    [DataContract]
    public enum WorkflowState
    {
        [EnumMember] Pending = 0,
        [EnumMember] InProgress = 1,
        [EnumMember] Completed = 2,
        [EnumMember] Failed = 3,
        [EnumMember] Cancelled = 4
    }

    [DataContract]
    public class OperationResult
    {
        // String properties - these work correctly with minOccurs="0"
        [DataMember]
        public string Description { get; set; }

        [DataMember]
        public string Notes { get; set; }

        // Enum property attempts - NONE of these produce minOccurs="0"
        
        [DataMember]
        public WorkflowState BasicEnumProperty { get; set; }

        [DataMember]
        public WorkflowState? NullableEnumProperty { get; set; }

        [DataMember]
        public Nullable<WorkflowState> ExplicitNullableEnum { get; set; }

        [DataMember(IsRequired = false)]
        public WorkflowState? IsRequiredFalseEnum { get; set; }

        [DataMember(IsRequired = false, EmitDefaultValue = false)]
        public WorkflowState? BothAttributesEnum { get; set; }

        [DataMember]
        public string AdditionalInfo { get; set; }
    }

    [ServiceContract]
    public interface ITestService
    {
        [OperationContract]
        OperationResult GetOperationResult();
    }

    public class TestService : ITestService
    {
        public OperationResult GetOperationResult()
        {
            return new OperationResult
            {
                Description = "Test operation",
                BasicEnumProperty = WorkflowState.Pending
            };
        }
    }
}

Program.cs:

using SoapCore;
using SoapCoreEnumIssue;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddSingleton<ITestService, TestService>();
builder.Services.AddSoapCore();

var app = builder.Build();

app.UseSoapEndpoint<ITestService>("/Service.svc", new SoapEncoderOptions());

app.Run();

SoapCoreEnumIssue.csproj:

<Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>net8.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="SoapCore" Version="1.2.1.11" />
  </ItemGroup>
</Project>

Generated WSDL (Problem Section)

Access the WSDL at http://localhost:5000/Service.svc?wsdl and observe the OperationResult complex type:

<xs:complexType name="OperationResult">
  <xs:sequence>
    <xs:element minOccurs="0" name="AdditionalInfo" nillable="true" type="xs:string"/>
    <xs:element type="tns:WorkflowState" name="BasicEnumProperty"/>
    <!-- ❌ Missing minOccurs="0" even though nillable="true" is present -->
    <xs:element nillable="true" type="tns:WorkflowState" name="BothAttributesEnum"/>
    <xs:element minOccurs="0" name="Description" nillable="true" type="xs:string"/>
    <!-- ❌ Missing minOccurs="0" even though nillable="true" is present -->
    <xs:element nillable="true" type="tns:WorkflowState" name="ExplicitNullableEnum"/>
    <!-- ❌ Missing minOccurs="0" despite IsRequired=false -->
    <xs:element nillable="true" type="tns:WorkflowState" name="IsRequiredFalseEnum"/>
    <xs:element minOccurs="0" name="Notes" nillable="true" type="xs:string"/>
    <!-- ❌ Missing minOccurs="0" even though nillable="true" is present -->
    <xs:element nillable="true" type="tns:WorkflowState" name="NullableEnumProperty"/>
  </xs:sequence>
</xs:complexType>

Notice that:

• String properties correctly have minOccurs="0"
• All nullable enum properties have nillable="true" but are missing minOccurs="0"
• The IsRequiredFalseEnum property explicitly sets IsRequired=false in the service but still lacks minOccurs="0" in the WSDL

Additional Notes

When generating client proxies with this WSDL using svcutil, all the nullable enum properties incorrectly generate as:

[System.Runtime.Serialization.DataMemberAttribute(IsRequired=true)]
public System.Nullable<TestService.WorkflowState> NullableEnumProperty { ... }

This forces clients to always include these fields in requests, defeating the purpose of making them optional.

[github-actions]

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