[Bug]: The JSON value could not be converted to System.DateOnly

[Bidou44]

Describe the bug

Everything was working fine with v6.5.0. After migrating to v6.6.1 or v6.6.2, I got the following exception

System.Text.Json.JsonException: The JSON value could not be converted to System.DateOnly.

I didn't change any line of code, just migrated the package.

Expected behavior

the json definition should load correctly. Instead, I got an error message.

Actual behavior

This is what I get

{
    "type": "https://tools.ietf.org/html/rfc9110#section-15.6.1",
    "title": "Internal Server Error",
    "status": 500,
    "detail": "An unhandled exception occurred",
    "instance": "/api/doc/v1.json",
    "traceId": "f0b3b9ac7ca1e1711f1ebfbb291f8385",
    "exception": "Swashbuckle.AspNetCore.SwaggerGen.SwaggerGeneratorException: Failed to generate Operation for action - (...). See inner exception\n ---> Swashbuckle.AspNetCore.SwaggerGen.SwaggerGeneratorException: Failed to generate schema for type - (...). See inner exception\n ---> System.Text.Json.JsonException: The JSON value could not be converted to System.DateOnly.\n   at System.Text.Json.ThrowHelper.ThrowJsonException_DeserializeUnableToConvertValue(Type propertyType)\n   at System.Text.Json.JsonSerializer.UnboxOnWrite[T](Object value)\n   at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.SerializeAsObject(Utf8JsonWriter writer, Object rootValue)\n   at System.Text.Json.JsonSerializer.WriteStringAsObject(Object value, JsonTypeInfo jsonTypeInfo)\n   at Swashbuckle.AspNetCore.SwaggerGen.JsonSerializerDataContractResolver.JsonConverterFunc(Object value, Type type)\n   at Swashbuckle.AspNetCore.SwaggerGen.JsonSerializerDataContractResolver.<>c__DisplayClass2_0.<GetDataContractForType>b__1(Object value)\n   at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateDefaultValue(DataContract dataContract, Type modelType, Object defaultValue)\n   at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchemaForMember(Type modelType, SchemaRepository schemaRepository, MemberInfo memberInfo, DataProperty dataProperty)\n   at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.CreateObjectSchema(DataContract dataContract, SchemaRepository schemaRepository)\n   at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.<>c__DisplayClass11_0.<GenerateConcreteSchema>b__3()\n   at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateReferencedSchema(DataContract dataContract, SchemaRepository schemaRepository, Func`1 definitionFactory)\n   at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateConcreteSchema(DataContract dataContract, SchemaRepository schemaRepository)\n   at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchemaForParameter(Type modelType, SchemaRepository schemaRepository, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo)\n   at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchema(Type modelType, SchemaRepository schemaRepository, MemberInfo memberInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo)\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateSchema(Type type, SchemaRepository schemaRepository, PropertyInfo propertyInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo)\n   --- End of inner exception stack trace ---\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateSchema(Type type, SchemaRepository schemaRepository, PropertyInfo propertyInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo)\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateRequestBodyFromBodyParameter(ApiDescription apiDescription, SchemaRepository schemaRepository, ApiParameterDescription bodyParameter)\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateRequestBody(ApiDescription apiDescription, SchemaRepository schemaRepository)\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperation(ApiDescription apiDescription, SchemaRepository schemaRepository)\n   --- End of inner exception stack trace ---\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperation(ApiDescription apiDescription, SchemaRepository schemaRepository)\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperations(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository)\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePaths(IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository)\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwaggerDocumentWithoutFilters(String documentName, String host, String basePath)\n   at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwaggerAsync(String documentName, String host, String basePath)\n   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)\n   at (...)
}

Steps to reproduce

No response

Exception(s) (if any)

System.Text.Json.JsonException: The JSON value could not be converted to System.DateOnly.

Swashbuckle.AspNetCore version

6.6.1 and upper

.NET Version

net8.0

Anything else?

No response

[martincostello]

Swashbuckle.AspNetCore 6.6 added support for the DateOnly type which was previously unknown to it as part of adding support for .NET 8.

Could you share an example of what value is trying to be (de)serialized to a DateOnly value and/or an API definition that causes this issue?

[Bidou44]

Unfortunately I don't have a minimal working example right now.
The Dto that is referenced in the exception looks like this, I don't know if that helps:

public class MyDto
{
    public DateOnly ActiveFrom { get; set; } = DateTimeHelper.Today;

    public DateOnly? InactiveFrom { get; set; }

    (...)
}

[martincostello]

I think the missing piece for us what is the string that's trying to be turned into a DateOnly - if it's genuinely invalid, then it might be that it was invalid before but just happened to work because it was just being treated as a string. Now with the knowledge of DateOnly, the existing invalid value is now being surfaced.

[Bidou44]

I understand your question but I don't know. I'm not doing any api calls, I'm just trying to load the swagger page where all APIs are listed http://localhost:8080/swagger/ui and the exception pops up. Was working fine with v6.5.0

How can I find the value it's trying to convert to DateOnly?

[martincostello]

I think the only way to get to the bottom of it is to provide a minimal repro project you can share with us that we can then debug. Alternatively, you could clone this repo and reference the project from source rather than NuGet and step through the code to where the exception is coming from.

[Bidou44]

After a long debugging, I finally found the problem:

public class MyDto
{
    public DateOnly ActiveFrom { get; set; }

    [DefaultValue(null)]
    public DateOnly? InactiveFrom { get; set; }
}

The problem here comes from the [DefaultValue(null)]. Was working fine with v6.5.0, breaks with 6.6.1.

Hope it helps.
Cheers.

[martincostello]

For clarity, does it work if you update to 6.6.2, or is it broken with that too?

[Bidou44]

No, it doesn't work with this version either.

I think we had this attribute so that the default value displayed in Swagger UI would not be filled (otherwise a random string would be displayed). It probably worked because for swagger DateOnly was handled like a "string" (?)
Now that 6.6.1 and upper supports DateOnly, perhaps the attribute is no longer needed to have an empty default value (when the type is nullable of course) ? I'll test it next week...

[Bidou44]

Removing that attribute fixed the problem, but then you have a default value in Swagger UI, which is probably not the default you want for a nullable value (but that is ok, I guess it always worked like this). But with version 6.5 and earlier you were able to have that behavior by applying the DefaultValue attribute. With 6.6.1 and later an exception is thrown, so a breaking change was introduced here.

Any fix soon?

[martincostello]

I haven't had the time to look into it yet.

Community contributions to investigate the bug and/or fix are welcome as it would speed things along.

[jgarciadelanoceda]

I am probably going to look at this issue

[martincostello]

#2941