通常我們需要按照一定的規(guī)則查詢數(shù)據(jù)庫，但是常常需要對數(shù)據(jù)里面的進(jìn)行統(tǒng)計(jì)鞠鲜，歸類什么的。
這時(shí)候就需要用到mongo 聚合了；
mongoose $subtract
- Subtract Numbers
{
"_id": 1,
"item": "abc",
"price": 10,
"fee": 2,
"discount": 5,
"date": ISODate("2014-03-01T08:00:00Z")
} {
"_id": 2,
"item": "jkl",
"price": 20,
"fee": 1,
"discount": 2,
"date": ISODate("2014-03-01T09:00:00Z")
}
db.sales.aggregate([{
$project: {
item: 1,
total: {
$subtract: [{
$add: ["$price", "$fee"]
}, "$discount"]
}
}
}])
result:
{ "_id" : 1, "item" : "abc", "total" : 7 }
{ "_id" : 2, "item" : "jkl", "total" : 19 }
- Subtract Two Dates
db.sales.aggregate([{
$project: {
item: 1,
dateDifference: {
$subtract: [new Date(), "$date"]
}
}
}])
result:
{ "_id" : 1, "item" : "abc", "dateDifference" : NumberLong("11713985194") }
{ "_id" : 2, "item" : "jkl", "dateDifference" : NumberLong("11710385194") }
