Created
March 28, 2012 21:40
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db.eval() and server-side updates on MongoDB with the Ruby driver
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| # Records the vote against 2 items. | |
| # Both parameters are strings | |
| def record_votes(winner_id, loser_id) | |
| # grab the connection from the underlying driver | |
| db = Mongoid::Config::master | |
| # a future improvement would be to store this away somewhere, perhaps as a constant | |
| # note: javascript comments added for the post: they are not in the real code | |
| f = """ | |
| function(winner_id, loser_id) { | |
| // will update one of the documents based on if it won the vote or not | |
| var update = function(id, win) { | |
| var doc = db.items.findOne({_id: ObjectId(id)}); | |
| if (!doc) return; // just ignore if can't find it | |
| // updated automatically be Mongoid but we need to do it ourselves here | |
| doc.updated_at = new Date(); | |
| // the simple updates that could have been done in-place | |
| doc.votes++; | |
| if (win) doc.wins++; else doc.losses++; | |
| // stats calculations. the actual calculation is not important. | |
| doc.percent_wins = Math.round(doc.wins / doc.votes * 100); | |
| doc.percent_losses = Math.round(doc.losses / doc.votes * 100); | |
| doc.rank = doc.percent_wins * (doc.votes >= #{ItemsController::VOTE_THRESHOLD} ? 100 : 10); | |
| db.items.save(doc); | |
| } | |
| // perform separate updates on each document | |
| update(winner_id, true); | |
| update(loser_id, false); | |
| } | |
| """ | |
| # note $eval has to be first | |
| db.command({:$eval => f, args: [winner_id, loser_id], nolock: true}) | |
| end |
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| > db.runCommand({ $eval: function(abool) { return abool; }, args: [false], nolock: true }); | |
| Tue Nov 22 11:55:02 [conn1] query test.$cmd ntoreturn:1 command: { $eval: function (abool) { | |
| return abool; | |
| }, args: [ false ], nolock: true } reslen:62 183ms | |
| { "retval" : false, "ok" : 1 } |
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