Cannot parse Orders data into Json

[dodongphure]

When I use GetOrders() to get Orders data, I want to parse these data into JSON objects as I am writing api for this. But unfortunately, the parsed JSON objects only has property entity_id, other properties do not exist.
Btw I found that OrderConverter class, seem only field entity_id is required when parsing.
So can we have another method or something like this in order to parse all properties into JSON?

Thanks!