Best practice for updating a structured resource via REST?

Question

I have a client-side interface that allows the user to perform multiple edits against a tree-like outline. I consider the aggregate of the records making up that outline, in totality, a single resource (/outlines/39) even though its parts could be accessed as separate resources via different URLs.

The problem is the user can edit existing nodes in the outline as well as add new nodes to the outline. Normally, when you edit something you PUT its changes and when you add something new you POST it; however, in some cases you'll want to wrap all the changes--including both adds and edits--in a single transaction. What are some practical ways people have handled this?

Even though the outline already exists and a PUT seems appropriate, the embedded adds violate the idempotence of the PUT. I'm not sure that POST seems appropriate either. For design purposes, I have decided not to save each discrete update the user makes though I guess this offers one solution. Still, there must be others who have dealt with my issue or have ideas about it.

Answer 1

Is there any way you could make the add idempotent? E.g. if nodes had a natural key, then when the client tried to add a node a second time you could do nothing.

Answer 2

How about: make a new resource: /outlines/39/transactions, and POST your transaction to that resource, e.g.

POST "addNode=node1, addNode=node2, editNode=node3,newName=foobar" to /outlines/39/transactions