Custom Scalar Support

Hi, I’ve been using the HotChocolate library for some time now and am getting around to trying out custom scalar types. When a scalar type is given a unique name such as “CustomLong”, it can be registered just fine and used within my other types as input/output.

public class CustomLongType : ScalarType
    {
        public CustomLongType() : base("CustomLong")
        {
        
        }
        ...
    }

Via your documentation, it mentions the ability to swap out the built-in base Scalar types. I have tried to swap out your guys’ long scalar type to be able to add my own custom behavior, but have not been able to do so. Defining my CustomLongType like such:

public class CustomLongType : ScalarType
    {
        public CustomLongType() : base("Long")
        {
        
        }
        ...
    }

This seems to fail to register the type correctly in TypeRegistry as the _namedTypes dictionary will pull back the built-in ScalarType for long {HotChocolate.Types.LongType}

private void TryUpdateNamedType(INamedType namedType)
{
	INamedType namedTypeRef = namedType;

	if (!_namedTypes.TryGetValue(namedType.Name, out namedTypeRef))
	{
		namedTypeRef = namedType;
		_namedTypes[namedTypeRef.Name] = namedTypeRef;
	}
        ...
}

Should there be something here to check for IsScalarType to swap with?

Is there a better way to do such swapping? Is this type of swap allowed? Let me know if I am doing something completely wrong!

[michaelstaib]

The scalar types are registered by the SchemaContextFactory. The schema context is the internal initialization context for the schema.

The factory has two functions that preregister scalar types (RegisterSpecScalarTypes and RegisterSpecScalarTypes).

All types that are preregistered by the SchemaContextFactory cannot be changed. This behavior is correct since we do not want people to meddle with the spec scalars or the introspection types.

What is wrong is to register the extended scalars here.

So my suggestion is to remove the RegisterExtendedScalarTypes from that class and create a new extensions method in SchemaConfigurationExtensions called RegisterExtendedScalarTypes that registers those types.

With that users of the API could register the package with one line of code and use HC like before or the could register just some of those types by manually registering them.

Tests

• Test that shows that the extended types are not registered without calling RegisterExtendedScalarTypes on ISchemaConfiguration
• Test that proves that custom scalars for can be registered.
• Test that proves that the spec scalars cannot be swapped out.
• Test that shows that all extended types are correctly registered when RegisterExtendedScalarTypes on ISchemaConfiguration is called.

Changelog

• Update the change log ([Unreleased] section)

Documentation

• We need to update the section https://hotchocolate.io/docs/next/custom-scalar-types Maybe we should rename that section to scalar types and then state what are the spec types (table) show what extended types we provide and how they can be registered. https://github.com/ChilliCream/hotchocolate-docs

[michaelstaib]

We also have a slack channel for questions etc …

https://join.slack.com/t/hotchocolategraphql/shared_invite/enQtNTA4NjA0ODYwOTQ0LTBkZjNjZWIzMmNlZjQ5MDQyNDNjMmY3NzYzZjgyYTVmZDU2YjVmNDlhNjNlNTk2ZWRiYzIxMTkwYzA4ODA5Yzg