Why are dates in match aggregate query being ignored?

aggregation-framework, mongodb

Solution

Remove the `$` prefix on the `$date` field of your `$match`:

{ $match: { 
    keywordGroupId: 75, 
    date: {$gte: ISODate("2013-01-01T00:00:00.0Z"), $lt: ISODate("2013-02-01T00:00:00.0Z")}
}},

You only use the `$` prefix when the field name is used in a value, not as a key.

Problem

I'm trying to run an aggregation statement in my mongo db. I have a document whose structure is (at least) as follows: ``` { "_id": ObjectId, "date": ISODate, "keywordGroupId": NumberLong, "ranking": NumberLong, } ``` I would like to run an aggregation statement that aggregates the 'ranking' field for a given 'keywordGroupId' and a given 'date' interval. I have been trying with the following aggregate command: ``` { aggregate : "KeywordHistory", pipeline : [ { $match: { keywordGroupId: 75 , "$date": {$gte: ISODate("2013-01-01T00:00:00.0Z"), $lt: ISODate("2013-02-01T00:00:00.0Z")}} }, { $group: { _id: { null }, count: { $sum: "$ranking" } } } ] } ``` This command executes without errors and returns a result. If I try to change the value for the 'keywordGroupId' field, the command returns a different value, so I assume that the $match statement works for that field (NumberLong). Though, if I change the 'date' range and I specify a time interval for which I don't have any data in the database, it still returns a result (I would actually expect an empty result set). So I have to assume that the $match statement is ignoring the date interval specified. Can anyone help me with this point?

Original source