Proper generation of c# enums using the the OpenAPI 3.x spec

[ghost]

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I'm using Swashbuckle.AspNetCore -Version 5.0.0-rc4

In my case I have the following issue:

I have a C# enum defined like so:
public enum ObjectState
{
Unchanged = 0,
Add = 1,
Update = 2,
Delete = 3
}

This get represented in the OpenAPI 3.x doc as
"components": {
"schemas": {
"ObjectState": {
"enum": [
0,
1,
2,
3
],
"type": "integer",
"format": "int32"
},

When I run the NSwag client generator all it has as a reference is the OpenAPI spec which of course is missing the name portion of the enum. NSwag generates the following object for the client which is basically unusable:

public enum ObjectState
{
    _0 = 0,
    _1 = 1,
    _2 = 2,
    _3 = 3
}

Would it be possible to use oneOf from the OpenAPI spec instead to properly represent a C# enum
See the discussion here:
OAI/OpenAPI-Specification#681

According to handrews the spec is not going to be changed regarding this issue and suggested using something like the following from the OpenAPI spec to represent the enum.
oneOf:

• enum: [1]
  title: Sunny
  description: Blue sky
• enum: [2]
  title: Cloudy
  description: Slightly overcast
• enum: [3]
  title: Rainy
  description: Take an umbrella with you

Thoughts? Work arounds???
Much appreciated
Kevin

[ghost]

I see there is a solution to this problem using Swashbuckle.AspNetCore.Filters so I'm closing.

[RouR]

Can you provide solution?

[WhitWaldo]

@RouR I use the following (would require a little tweaking to yield the original ask above):

[DataContract]
public enum MyEnum {
  [EnumMember(Value="red")]
  Red,
  [EnumMember(Value="blue"]
  Blue
}

The filter itself:

public class DescribeEnumMemberValues : ISchemaFilter
    {
        public void Apply(OpenApiSchema schema, SchemaFilterContext context)
        {
            if (context.Type.IsEnum)
            {
                schema.Enum.Clear();

                //Retrieve each of the values decorated with an EnumMember attribute
                foreach (var member in context.Type.GetMembers())
                {
                    var memberAttr = member.GetCustomAttributes(typeof(EnumMemberAttribute), false).FirstOrDefault();
                    if (memberAttr != null)
                    {
                        var attr = (EnumMemberAttribute) memberAttr;
                        schema.Enum.Add(new OpenApiString(attr.Value));
                    }
                }
            }
        }
    }

And in your Startup, register the filter with:

services.AddSwaggerGen(c => {
  c.SchemaFilter<DescribeEnumMemberValues>();
});

The resulting enum will be described using the values within the EnumMember attribute values instead of their indices.

[martinRocks]

I wish there was a better way to do this, but using WhitWaldo solution I came up with this. I like it a bit more because it uses the Description attribute.

And in your Startup, register the filter with:

services.AddSwaggerGen(c => {
  c.SchemaFilter<DescribeEnumMemberValues>();
});

public enum ConfidenceEnum
{
    [Description("Very xx")]
    Very = 1,

    [Description("SomeWhat xx")]
    SomeWhat,

    [Description("Low xx")]
    Low
}

public class DescribeEnumMemberValues : ISchemaFilter
{
    public void Apply(OpenApiSchema schema, SchemaFilterContext context)
    {
        if (context.Type.IsEnum)
        {
            var dictionary = Enum.GetValues(context.Type)
                .Cast<object>()
                .ToDictionary(value => (int)value, value => GetEnumDescription((Enum)value));
            schema.Description = "Enum values:" + string.Join(", ", dictionary.Select(x => $"{x.Key} = {x.Value}"));
        }
    }

    private static string GetEnumDescription(Enum value)
    {
        var fi = value.GetType().GetField(value.ToString());

        if (fi == null) return value.ToString(); 
        var attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);

        return attributes.Length > 0 ? attributes[0].Description : value.ToString(); 
    }
}

It produces this:

"ConfidenceEnum": {
                "enum": [
                    1,
                    2,
                    3
                ],
                "type": "integer",
                "description": "Enum values:1 = Very xx, 2 = SomeWhat xx, 3 = Low xx",
                "format": "int32"
            }