您$unwind
数组,如果你想看看内容为“分组”,在其中:
db.flights.aggregate([
{ "$unwind": "$dates" },
{ "$group": {
"_id": { "carrier": "$carrier", "flightnumber": "$flightnumber", "date": "$dates" },
"count": { "$sum": 1 },
"_ids": { "$addToSet": "$_id" }
}},
{ "$match": { "count": { "$gt": 1 } } },
{ "$unwind": "$_ids" },
{ "$group": { "_id": "$_ids" } }
])
那请问其实告诉你哪些文件里的“重叠”所在,因为“同一日期“以及您关心的其他相同分组键值有一个”计数“,其发生超过一次。指示重叠。
$match
之后的任何内容实际上只是用于“展示”,因为如果您只想查看重叠,则没有意见报告多个重叠的相同_id
值。事实上,如果你想看到他们在一起,最好离开“分组集”单独。现在
您可以添加一个$lookup
到,如果检索实际的文件是对你很重要:
db.flights.aggregate([
{ "$unwind": "$dates" },
{ "$group": {
"_id": { "carrier": "$carrier", "flightnumber": "$flightnumber", "date": "$dates" },
"count": { "$sum": 1 },
"_ids": { "$addToSet": "$_id" }
}},
{ "$match": { "count": { "$gt": 1 } } },
{ "$unwind": "$_ids" },
{ "$group": { "_id": "$_ids" } },
}},
{ "$lookup": {
"from": "flights",
"localField": "_id",
"foreignField": "_id",
"as": "_ids"
}},
{ "$unwind": "$_ids" },
{ "$replaceRoot": {
"newRoot": "$_ids"
}}
])
而且即使做了$replaceRoot
或$project
使其返回整个文档。或者你甚至可以用$$ROOT
完成$addToSet
,如果它不是大小问题。
但总体来说,前三个流水线阶段或大部分只是“第一个”。如果你想用“跨文件”的方式处理数组,那么主操作员仍然是$unwind
。
或者一个更“报告”之类的格式:
db.flights.aggregate([
{ "$addFields": { "copy": "$$ROOT" } },
{ "$unwind": "$dates" },
{ "$group": {
"_id": {
"carrier": "$carrier",
"flightNumber": "$flightNumber",
"dates": "$dates"
},
"count": { "$sum": 1 },
"_docs": { "$addToSet": "$copy" }
}},
{ "$match": { "count": { "$gt": 1 } } },
{ "$group": {
"_id": {
"carrier": "$_id.carrier",
"flightNumber": "$_id.flightNumber",
},
"overlaps": {
"$push": {
"date": "$_id.dates",
"_docs": "$_docs"
}
}
}}
])
这将各组内汇报重叠的日期,告诉你哪些文件载有重叠:
{
"_id" : {
"carrier" : "abc",
"flightNumber" : 123.0
},
"overlaps" : [
{
"date" : ISODate("2015-01-03T00:00:00.000Z"),
"_docs" : [
{
"_id" : ObjectId("5977f9187dcd6a5f6a9b4b97"),
"carrier" : "abc",
"flightNumber" : 123.0,
"dates" : [
ISODate("2015-01-03T00:00:00.000Z"),
ISODate("2015-01-04T00:00:00.000Z"),
ISODate("2015-01-05T00:00:00.000Z")
]
},
{
"_id" : ObjectId("5977f9187dcd6a5f6a9b4b96"),
"carrier" : "abc",
"flightNumber" : 123.0,
"dates" : [
ISODate("2015-01-01T00:00:00.000Z"),
ISODate("2015-01-02T00:00:00.000Z"),
ISODate("2015-01-03T00:00:00.000Z")
]
}
]
}
]
}