[rest-practices] Read-only fields in a representation type

[Eoghan Glynn]

Folks,

A REST design question ... suppose we're using the same representation
in a number of different contexts:

1. to capture client input to resource creation (i.e. the payload in the
POST /collection request)

2. to encode a state change initiated by the client (i.e. the payload
for the PUT /collection/id request)

3. to represent the complete resource state sent back to the client
(i.e. response to GET /collection/id)

Say the representations used in cases #1 and #2 are a proper subset of
#3, because some of the fields must be computed, or have fixed
defaults/initial values. So the question is, how do we enforce this
constraint?

We could define separate types to ensure that only those fields that
really can be set by the client are used in the POST and PUT, and then
enforce via schema validation or whatever. 

Or is best to be tolerant and just silently discard any read-only fields
specified in the first two cases?

Cheers,
Eoghan