There doesn't appear to be a way to map built-in functions using this API. I'm trying to map the FORMAT function...and the API tries to pre-pend the default schema when invoking it which is incorrect and results in an exception.
To support my scenario, the EdmPayloadFunction.IsBuiltIn property needs to be set to TRUE (by either the StoreFunctionBuilder or the FunctionsConvention class).
Is there any chance that this will be supported in the future? As is, unfortunately I cannot use the API, which is a shame as it makes registration so simple!
public static string Format(decimal value, string format)
throw new NotSupportedException("This method is not intended to be called directly.");