Question

我拥有一个包含历史数据的MongoDB收集器,有id和时间。

I want to delete data from the collection older than a specific timestamp. But for every id at least one document (the newest) must stay in the collection.

附录一

{"id" : "11", "timestamp" : ISODate("2011-09-09T10:27:34.785Z")} //1
{"id" : "11", "timestamp" : ISODate("2011-09-08T10:27:34.785Z")} //2

{"id" : "22", "timestamp" : ISODate("2011-09-05T10:27:34.785Z")} //3
{"id" : "22", "timestamp" : ISODate("2011-09-01T10:27:34.785Z")} //4

... and I want to delete documents having a timestamp older than 2011-09-07 then 1 and 2 should not be deleted because they are newer. 4 should be deleted because it is older, but 3 should not be deleted (although it is older) because at least one document per id should stay in the collection.

Does anyone know how I can do this with casbah and/or on the mongo console?

Regards, Christian

Answer 1

我可以考虑几种方法。第一,尝试:

var cutoff = new ISODate("2011-09-07T00:00:00.000Z");
db.testdata.find().forEach(function(data) {
    if (data.timestamp.valueOf() < cutoff.valueOf()) {
        // A candidate for deletion
        if (db.testdata.find({"id": data.id, "timestamp": { $gt: data.timestamp }}).count() > 0) {
            db.testdata.remove({"_id" : data._id});
         }
    }
});

这是你想要的工作。或者,你也可以利用“地图”工作。将这段文字编为:

var map = function() {
    emit(this.id, {
        ref: this._id,
        timestamp: this.timestamp
    });
};


var reduce = function(key, values) {
    var cutoff = new ISODate("2011-09-07T00:00:00.000Z");
    var newest = null;
    var ref = null;
    var i;
    for (i = 0; i < values.length; ++i) {
        if (values[i].timestamp.valueOf() < cutoff.valueOf()) {
            // falls into the delete range
            if (ref == null) {
                ref = values[i].ref;
                newest = values[i].timestamp;
            } else if (values[i].timestamp.valueOf() > newest.valueOf()) {
                // This one is newer than the one we are currently saving.
                // delete ref
                db.testdata.remove({_id : ref});
                ref = values[i].ref;
                newest = values[i].timestamp;
            } else {
                // This one is older
                // delete values[i].ref
                db.testdata.remove({_id : values[i].ref});
            }
        } else if (ref == null) {
            ref = values[i].ref;
            newest = values[i].timestamp;
        }
    }
    return { ref: ref, timestamp: newest };
};

将上述档案输入壳体:load(”file.js”;

然后管理:db.testdata.mapReduce (map, reduction,{out: “results”};

然后删除图Reduce输出:db.results.drop()。

友情链接