我想找到一种将mongoDB查询的3个评级组合在一起的简便方法。具体来说，有一种方法可以将3个汇总调用合并为一个。因此，例如，我有以下数据。其中列出了电影的收视率，无论是imbd.rating，tomato.rating还是metacritic，我想为每个收视率找到前2名电影。最下面的查询是我如何基于Tomato.rating
获取前2个结果数据
{
"title": "Once Upon a Time in the West",
"year": 1968,
"rated": "PG-13",
"runtime": 175,
"countries": [
"Italy",
"USA",
"Spain"
],
"genres": [
"Western"
],
"director": "Sergio Leone",
"writers": [
"Sergio Donati",
"Sergio Leone",
"Dario Argento",
"Bernardo Bertolucci",
"Sergio Leone"
],
"actors": [
"Claudia Cardinale",
"Henry Fonda",
"Jason Robards",
"Charles Bronson"
],
"plot": "Epic story of a mysterious stranger with a harmonica who joins forces with a notorious desperado to protect a beautiful widow from a ruthless assassin working for the railroad.",
"poster": "http://ia.media-imdb.com/images/M/MV5BMTEyODQzNDkzNjVeQTJeQWpwZ15BbWU4MDgyODk1NDEx._V1_SX300.jpg",
"imdb": {
"id": "tt0064116",
"rating": 8.6,
"votes": 201283
},
"tomato": {
"meter": 98,
"image": "certified",
"rating": 9,
"reviews": 54,
"fresh": 53,
"consensus": "A landmark Sergio Leone spaghetti western masterpiece featuring a classic Morricone score.",
"userMeter": 95,
"userRating": 4.3,
"userReviews": 64006
},
"metacritic": 80,
"awards": {
"wins": 4,
"nominations": 5,
"text": "4 wins \u0026 5 nominations."
},
"type": "movie"
},
{
"title": "A Million Ways to Die in the West",
"year": 2014,
"rated": "R",
"runtime": 116,
"countries": [
"USA"
],
"genres": [
"Comedy",
"Western"
],
"director": "Seth MacFarlane",
"writers": [
"Seth MacFarlane",
"Alec Sulkin",
"Wellesley Wild"
],
"actors": [
"Seth MacFarlane",
"Charlize Theron",
"Amanda Seyfried",
"Liam Neeson"
],
"plot": "As a cowardly farmer begins to fall for the mysterious new woman in town, he must put his new-found courage to the test when her husband, a notorious gun-slinger, announces his arrival.",
"poster": "http://ia.media-imdb.com/images/M/MV5BMTQ0NDcyNjg0MV5BMl5BanBnXkFtZTgwMzk4NTA4MTE@._V1_SX300.jpg",
"imdb": {
"id": "tt2557490",
"rating": 6.1,
"votes": 126592
},
"tomato": {
"meter": 33,
"image": "rotten",
"rating": 4.9,
"reviews": 188,
"fresh": 62,
"consensus": "While it offers a few laughs and boasts a talented cast, Seth MacFarlane's overlong, aimless A Million Ways to Die in the West is a disappointingly scattershot affair.",
"userMeter": 40,
"userRating": 3,
"userReviews": 62945
},
"metacritic": 44,
"awards": {
"wins": 0,
"nominations": 6,
"text": "6 nominations."
},
"type": "movie"
},
{
"title": "Wild Wild West",
"year": 1999,
"rated": "PG-13",
"runtime": 106,
"countries": [
"USA"
],
"genres": [
"Action",
"Western",
"Comedy"
],
"director": "Barry Sonnenfeld",
"writers": [
"Jim Thomas",
"John Thomas",
"S.S. Wilson",
"Brent Maddock",
"Jeffrey Price",
"Peter S. Seaman"
],
"actors": [
"Will Smith",
"Kevin Kline",
"Kenneth Branagh",
"Salma Hayek"
],
"plot": "The two best hired guns in the West must save President Grant from the clutches of a nineteenth-century inventor-villain.",
"poster": "http://ia.media-imdb.com/images/M/MV5BNDI5NDk5MjgxMl5BMl5BanBnXkFtZTcwNjI1MTUyMQ@@._V1_SX300.jpg",
"imdb": {
"id": "tt0120891",
"rating": 4.8,
"votes": 124558
},
"tomato": {
"meter": 17,
"image": "rotten",
"rating": 4.1,
"reviews": 130,
"fresh": 22,
"consensus": "Bombastic, manic, and largely laugh-free, Wild Wild West is a bizarre misfire in which greater care was lavished upon the special effects than on the script.",
"userMeter": 28,
"userRating": 2.7,
"userReviews": 463740
},
"metacritic": 38,
"awards": {
"wins": 10,
"nominations": 11,
"text": "10 wins \u0026 11 nominations."
},
"type": "movie"
},
{
"title": "West Side Story",
"year": 1961,
"rated": "UNRATED",
"runtime": 152,
"countries": [
"USA"
],
"genres": [
"Crime",
"Drama",
"Musical"
],
"director": "Jerome Robbins, Robert Wise",
"writers": [
"Ernest Lehman",
"Arthur Laurents",
"Jerome Robbins"
],
"actors": [
"Natalie Wood",
"Richard Beymer",
"Russ Tamblyn",
"Rita Moreno"
],
"plot": "Two youngsters from rival New York City gangs fall in love, but tensions between their respective friends build toward tragedy.",
"poster": "http://ia.media-imdb.com/images/M/MV5BMTM0NDAxOTI5MF5BMl5BanBnXkFtZTcwNjI4Mjg3NA@@._V1_SX300.jpg",
"imdb": {
"id": "tt0055614",
"rating": 7.6,
"votes": 67824
},
"awards": {
"wins": 18,
"nominations": 11,
"text": "Won 10 Oscars. Another 18 wins \u0026 11 nominations."
},
"type": "movie"
},
{
"title": "Slow West",
"year": 2015,
"rated": "R",
"runtime": 84,
"countries": [
"UK",
"New Zealand"
],
"genres": [
"Action",
"Thriller",
"Western"
],
"director": "John Maclean",
"writers": [
"John Maclean"
],
"actors": [
"Kodi Smit-McPhee",
"Michael Fassbender",
"Ben Mendelsohn",
"Aorere Paki"
],
"plot": "A young Scottish man travels across America in pursuit of the woman he loves, attracting the attention of an outlaw who is willing to serve as a guide.",
"poster": "http://ia.media-imdb.com/images/M/MV5BNTYxNDA5ODk5NF5BMl5BanBnXkFtZTgwNzMwMzIwNTE@._V1_SX300.jpg",
"imdb": {
"id": "tt3205376",
"rating": 7,
"votes": 19101
},
"tomato": {
"meter": 92,
"image": "certified",
"rating": 7.5,
"reviews": 115,
"fresh": 106,
"consensus": "Slow West serves as an impressive calling card for first-time writer-director John M. Maclean -- and offers an inventive treat for fans of the Western.",
"userMeter": 75,
"userRating": 3.7,
"userReviews": 9850
},
"metacritic": 72,
"awards": {
"wins": 2,
"nominations": 9,
"text": "2 wins \u0026 9 nominations."
},
"type": "movie"
},
{
"title": "An American Tail: Fievel Goes West",
"year": 1991,
"rated": "G",
"runtime": 75,
"countries": [
"USA"
],
"genres": [
"Animation",
"Adventure",
"Family"
],
"director": "Phil Nibbelink, Simon Wells",
"writers": [
"Flint Dille",
"Charles Swenson",
"David Kirschner"
],
"actors": [
"Phillip Glasser",
"James Stewart",
"Erica Yohn",
"Cathy Cavadini"
],
"plot": "A family of Emigre mice decide to move out to the west, unaware that they are falling into a trap perpetrated by a smooth talking cat.",
"poster": "http://ia.media-imdb.com/images/M/MV5BMTYzODMxNTUyNF5BMl5BanBnXkFtZTcwMTAwMzQyMQ@@._V1_SX300.jpg",
"imdb": {
"id": "tt0101329",
"rating": 6.4,
"votes": 16013
},
"awards": {
"wins": 0,
"nominations": 0,
"text": ""
},
"type": "movie"
},
tomato.rating得到
db.MovieData.aggregate([
{ "$unwind": "$tomato" },
{ "$sort": { "tomato.meter": -1 } },
{ "$limit": 2 },
{"$project": {title:1, "tomato.meter":1}},
])
imbd
db.MovieData.aggregate([
{ "$sort": { "imdb.rating": -1 } },
{ "$limit": 2 },
{"$project": {title:1, "imdb.rating":1}},
])
元批评家
db.MovieData.aggregate([
{ "$sort": { "metacritic": -1 } },
{ "$limit": 2 },
{"$project": {title:1, "metacritic":1}},
])
答案 0 :(得分：1)
这类“有限” 操作非常适合$facet：
db.MovieData.aggregate([
{ "$facet": {
"tomato": [
{ "$sort": { "tomato.meter": -1 } },
{ "$limit": 2 },
{"$project": {title:1, "tomato.meter":1}},
],
"imdb": [
{ "$sort": { "imdb.rating": -1 } },
{ "$limit": 2 },
{"$project": {title:1, "imdb.rating":1}},
],
"metacrtic": [
{ "$sort": { "metacritic": -1 } },
{ "$limit": 2 },
{"$project": {title:1, "metacritic":1}},
]
}}
])
从问题中的数据返回：
{
"tomato" : [
{
"_id" : ObjectId("5c80979542dd84d91e5547d9"),
"title" : "Once Upon a Time in the West",
"tomato" : {
"meter" : 98
}
},
{
"_id" : ObjectId("5c80979542dd84d91e5547dd"),
"title" : "Slow West",
"tomato" : {
"meter" : 92
}
}
],
"imdb" : [
{
"_id" : ObjectId("5c80979542dd84d91e5547d9"),
"title" : "Once Upon a Time in the West",
"imdb" : {
"rating" : 8.6
}
},
{
"_id" : ObjectId("5c80979542dd84d91e5547dc"),
"title" : "West Side Story",
"imdb" : {
"rating" : 7.6
}
}
],
"metacrtic" : [
{
"_id" : ObjectId("5c80979542dd84d91e5547d9"),
"title" : "Once Upon a Time in the West",
"metacritic" : 80
},
{
"_id" : ObjectId("5c80979542dd84d91e5547dd"),
"title" : "Slow West",
"metacritic" : 72
}
]
}
只要results are "small"，就可以用这种方式运行多个管道。
如果结果大，则最好运行独立的查询，最好并行运行（例如，在NodeJS的Promise.all()下）并组合结果（作为Promise.all()例如）。
尽管这实际上需要更多的数据库连接，但是并行处理通常可以消除额外的开销。当然，这意味着合并的结果（尤其是从游标处理的结果）不会导致响应上的BSON limit被破坏。
注意：
tomato是Object而不是Array，因此您不必使用$unwind