How to aggregate by date when a full timestamp is given in aggregation framework?

Question

I have a collection of errors, so that every error carries a date field. How can I aggregate/count/group the errors by DAY only (i.e. exclude the time of the da

Answer 1

You can convert your timestamp field to string with specific date format by using $project (aggregation)

aggregate([
    {
        '$project': {
            newFieldName: {'$dateToString': {format: '%Y-%m-%d', date: '$yourDateFieldName'}}
        }
    }, {
        '$group': {
            _id: {newFieldName: '$newFieldName'},
            viewCount: {'$sum': 1}
        }
    }, 
    {'$sort': {'_id.newFieldName': 1}}
], {})