Mongodb, group by datediff and getting hour

From what I understood in your question (you actually need to provide a sample couple of documents with your schema) if your Traitement model has the following structure, for instance:

/* 0 */{    "_id" : 1,    "user" : "abc",    "dateEntre" : ISODate("2014-03-01T08:00:00.000Z"),    "dateSortie" : ISODate("2014-03-01T13:00:00.000Z")}/* 1 */{    "_id" : 2,    "user" : "jkl",    "dateEntre" : ISODate("2014-03-01T08:00:00.000Z"),    "dateSortie" : ISODate("2014-03-01T10:30:00.000Z")}/* 2 */{    "_id" : 3,    "user" : "jkl",    "dateEntre" : ISODate("2014-03-01T12:00:00.000Z"),    "dateSortie" : ISODate("2014-03-01T18:00:00.000Z")}

Your aggregation framework would have a single $project pipeline operation where you get the difference between the two dates by using the $subtract operator and then transform that date difference in milliseconds to hours by using the $divide operator. The last stage in your pipeline will be to use the $group operator to group the documents from the previous pipeline and $sum the hours in date difference:

Traitement.aggregate([     {         $project: {             user: 1,                         dateDifference: {                 $divide: [{                     $subtract: [ "$dateSortie", "$dateEntre" ]                    }, 1000*60*60                ]             }         }    },    {         $group: {             _id: "$user",                         total : {                 $sum : "$dateDifference"            }        }    } ])

Results:

/* 0 */{    "result" : [         {            "_id" : "jkl",            "total" : 8.5        },         {            "_id" : "abc",            "total" : 5        }    ],    "ok" : 1}