您可以使用$lookup
(多重)从多个集合中获取记录:
例如:
如果您有更多的集合(我在这里为演示而有3个集合, 您可以拥有超过3个), 我想要从3个集合中获取数据到单个对象中:
集合如下所示:
db.doc1.find().pretty();
{
"_id" : ObjectId("5901a4c63541b7d5d3293766"),
"firstName" : "shubham",
"lastName" : "verma"
}
db.doc2.find().pretty();
{
"_id" : ObjectId("5901a5f83541b7d5d3293768"),
"userId" : ObjectId("5901a4c63541b7d5d3293766"),
"address" : "Gurgaon",
"mob" : "9876543211"
}
db.doc3.find().pretty();
{
"_id" : ObjectId("5901b0f6d318b072ceea44fb"),
"userId" : ObjectId("5901a4c63541b7d5d3293766"),
"fbURLs" : "http://www.facebook.com",
"twitterURLs" : "http://www.twitter.com"
}
现在您的查询将如下所示:
db.doc1.aggregate([
{ $match: { _id: ObjectId("5901a4c63541b7d5d3293766") } },
{
$lookup:
{
from: "doc2",
localField: "_id",
foreignField: "userId",
as: "address"
}
},
{
$unwind: "$address"
},
{
$project: {
__v: 0,
"address.__v": 0,
"address._id": 0,
"address.userId": 0,
"address.mob": 0
}
},
{
$lookup:
{
from: "doc3",
localField: "_id",
foreignField: "userId",
as: "social"
}
},
{
$unwind: "$social"
},
{
$project: {
__v: 0,
"social.__v": 0,
"social._id": 0,
"social.userId": 0
}
}
]).pretty();
那么您的结果将是:
{
"_id" : ObjectId("5901a4c63541b7d5d3293766"),
"firstName" : "shubham",
"lastName" : "verma",
"address" : {
"address" : "Gurgaon"
},
"social" : {
"fbURLs" : "http://www.facebook.com",
"twitterURLs" : "http://www.twitter.com"
}
}
如果您希望从每个集合获取所有记录,则应从查询中删除以下行:
{
$project: {
__v: 0,
"address.__v": 0,
"address._id": 0,
"address.userId": 0,
"address.mob": 0
}
}
{
$project: {
"social.__v": 0,
"social._id": 0,
"social.userId": 0
}
}
移除上述代码后,您将得到以下所有记录:
{
"_id" : ObjectId("5901a4c63541b7d5d3293766"),
"firstName" : "shubham",
"lastName" : "verma",
"address" : {
"_id" : ObjectId("5901a5f83541b7d5d3293768"),
"userId" : ObjectId("5901a4c63541b7d5d3293766"),
"address" : "Gurgaon",
"mob" : "9876543211"
},
"social" : {
"_id" : ObjectId("5901b0f6d318b072ceea44fb"),
"userId" : ObjectId("5901a4c63541b7d5d3293766"),
"fbURLs" : "http://www.facebook.com",
"twitterURLs" : "http://www.twitter.com"
}
}