Fetch snapshot of previous version about sharedb HOT 8 CLOSED

@g-borgulya @codingisacopingstrategy See this related thread josephg/ShareJS#12

From there, here's an implementation of getSnapshotAtRevision by @luto . The algorithm is:

• Fetch the current snapshot
• Fetch the ops between the current snapshot and the desired snapshot
• For each op in reverse order, invert it and apply it to the snapshot.

Here's a copy of the implementation (authored by @luto):

function getSnapshotAtRevision(docname, v, cb)
{
  var snapshot
    , ops = []

  async.waterfall(
    [
      // get latest revision
      function (cb)
      {
        model.getSnapshot(docname,
          function (err, _snapshot)
          {
            snapshot = _snapshot;
            cb(err);
          }
        );
      },
      // get ops that happend between `v` and `snapshot.v`
      function (cb)
      {
        if(v == snapshot.v)
          return cb();

        model.getOps(docname, v, snapshot.v,
          function (err, _ops)
          {
            ops = _ops;
            cb(err);
          }
        );
      },
      // invert and apply ops
      function (cb)
      {
        var json = sharejs.types.json;
        var content = snapshot.snapshot;
        var err = null;

        try
        {
          for (var i = ops.length - 1; i >= 0; i--) // reverse order
          {
            var op = ops[i].op;
            op = json.invert(op);
            content = json.apply(content, op);
          }
        }
        catch (_err)
        {
          err = _err;
        }

        cb(err, content);
      }
    ],
    cb
  );
}

from sharedb.

@codingisacopingstrategy do you have a workaround for this?

from sharedb.

Nice!! Thank you, @curran .

from sharedb.

@g-borgulya My pleasure! It would be amazing to integrate something like this into the project. One possible stumbling block is that I'm not sure all OT Types are invertable. Maybe there could be a variant that builds up the doc by replaying all ops in the forward direction from the beginning.

from sharedb.

I started packaging the above code into a library: https://github.com/curran/sharedb-snapshot/tree/master

from sharedb.

I agree that this would be a useful feature. I'm implementing a search and replace feature and in this case it would be useful being able to apply the replace operations on the snapshot version at the time of the search; applying the replace operations on the current version could not work if a change is applied in the meantime.

from sharedb.

@curran nice, thank you ;)

from sharedb.

This was implemented in #220

from sharedb.