Hi,
It depends if the structure of the data you want to post is the same as the one your retrieve with a GET, and if it fits with the underlying model. In this case, the same serializer can be used for both operations. Pay
attention however that things can be more complex if the involved model uses relations. In this case, using the same serializer is not always applicable.
If not possible, you'll need to define one for data retrieval (you can configure it so that all fields are read-only to be sure it will not be used incorrectly) and another one to model the data you'll send for a POST.
Eric