On Feb 6, 2014, at 2:07 PM, Jo-Erlend Schinstad <[email protected]> wrote:
> So; is this possible now or will it be? Just to be clear; I'm not asking > for relationships between documents, but merely a guarantee that a group of > documents are updated simultaneously or not at all. Probably not. You could implement transactional behavior on something like a single CouchDB node, but it's not possible to guarantee it when documents are being replicated between nodes, or in a multi-node cluster like BigCouch or Cloudant. (If you refer to the CAP Theorem, this is a prominent side effect of the Consistency sacrifices that CouchDB and related distributed databases make.) There are other ways to model trees. The simplest is to just store a "parent" reference in each document. This results in unordered sibling nodes, though. If you need ordering, you can add an "order" property to each node, and then sort siblings by its value. To move a node in the sibling order, you change its "order" property to something in between its new left and right siblings'. The obvious types of values to use are floating-point numbers, but eventually you run out of precision. I've also heard people propose strings — if you need to move a node between siblings "a" and "ab" you can give it the order value "am". —Jens
