MongoDB aggregate return count of 0 if no results

Question

I have the following MongoDB query that groups by date and result and gives a count. I\'d like to have the query also return a count of 0 for a particular date and result if da

Answer 1

If I correctly understand what do you want, you could try this:

db.builds.aggregate([
    { $project: 
        { 
            time: 1,
            projectedData: { $ifNull: ['$data.buildResult', 'none'] } 
        } 
    },

    { $group: { 
        _id: { 
            month: { $month: "$time" },
            day: { $dayOfMonth: "$time" },
            year: { $year: "$time" }, 
            buildResult: "$projectedData"
        },
        count: { $sum: { $cond: [ { $eq: [ "$projectedData", "none" ] }, 0, 1 ] } }
    } },

    { $sort: { "_id.year": 1, "_id.month": 1, "_id.day": 1 } }
])

Update:
You want to get from output more documents that been in input, it is possible only with unwind operator that works with arrays, but you haven't any arrays, so as I know it is impossible to get more documents in your case. So you should add some logic after query result to create new data for existing dates with 0 count for another type of buildResult...