IOrder.Quantity meaning and behaviour

[misova]

I made some research about behavior of IOrder.Quantity
when performing changes on the order by calling ChangeOrder(..).
Everything was tested for Unmanaged mode.

I found that:
A:
IOrder.Quantity could be seen like "MaxFillableQuantity" - meaning is it is the max value, where position of the order can grow.

When calling ChangeOrder(...) there are 2 possible scenarios:
B1:
If (parameter Quantity > Filled) -> sets new maximum position that order can reach
B2
If (parameter Quantity <= Filled) -> this makes order immediately OrderState.Filled, which is final state and no more changes are possible on such order. It behaves similarly to cancellation of the order.

What I found new and interesting:
Very interesting is, that we can sucessfully change Quantity of the existing order to value 0 (or any other value < Filled). In case we see IOrder.Quantity as "MaxFillableQuantity", this is acceptable and makes some sense. But it is really not very intuitive.

Can you please confirm each one A, B1, B2 they are fully correct or not?

[NinjaTrader_ChelseaB]

Hello misova,

Thank you for your post.

A) This is correct, the quantity of the order is the maximum total quantity that can fill.

B) Also correct, changing the quantity of the order will increase the maximum total quantity that can fill.

B2) Also correct, changing the quantity to less than the current filled amount will cause the orderState of the order to become instantly filled. Any further change attempts will result in an overfill.