If else if cond in mongodb aggregation
You can use $switch aggregation instead.
Schedul.aggregate([ { "$match": { "flag": 1 }}, { "$project": { "name": "$name", "day_of_week": { "$switch": { "branches": [ { "case": { "$eq": ["$day_of_week", 0] }, "then": "Sunday" }, { "case": { "$eq": ["$day_of_week", 1] }, "then": "Monday" }, { "case": { "$eq": ["$day_of_week", 2] }, "then": "Tuesday" }, { "case": { "$eq": ["$day_of_week", 3] }, "then": "Wednesday" }, { "case": { "$eq": ["$day_of_week", 4] }, "then": "Thrusday" }, { "case": { "$eq": ["$day_of_week", 5] }, "then": "Friday" } ], "default": "Saturday" } } }}])