Overview

This repository is for documenting and demonstrating a bug in the 1.0.0 version of Azure/azure-functions-openapi-extension.

When attempting to respond with a model that has a recursive object reference there is a side effect where other properties can no longer carry the same type.

For example:

public sealed class GroupModel
{
    public GroupModel? ChildGroup { get; set; }
    public UserModel? Owner { get; set; }
    public UserModel? CoOwner { get; set; }
}

public sealed class UserModel
{
    public Guid Id { get; set; }
}

In the example above, a group can have a child group, an owner, and a co-owner. This leads to the following exception when attempting to generate the Swagger:

An item with the same key has already been added. Key: userModel

   at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior)
   at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.RecursiveObjectTypeVisitor.ProcessProperties(IOpenApiSchemaAcceptor instance, String schemaName, Dictionary`2 properties, NamingStrategy namingStrategy)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.RecursiveObjectTypeVisitor.Visit(IAcceptor acceptor, KeyValuePair`2 type, NamingStrategy namingStrategy, Attribute[] attributes)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Visitors.OpenApiSchemaAcceptor.Accept(VisitorCollection collection, NamingStrategy namingStrategy)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.DocumentHelper.GetOpenApiSchemas(List`1 elements, NamingStrategy namingStrategy, VisitorCollection collection)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.Document.Build(Assembly assembly, OpenApiVersionType version)
   at Microsoft.Azure.WebJobs.Extensions.OpenApi.OpenApiTriggerFunctionProvider.RenderSwaggerDocument(HttpRequest req, String extension, ExecutionContext ctx, ILogger log)

However, if you remove the ChildGroup from the GroupModel definition, the exception disappears. You can also get rid of the exception by removing either Owner or CoOwner from the definition.