[英]MongoDB - $sum in multiple collections
I have many collections. 我有很多收藏。 The view of these collections is the same as the JSON.
这些集合的视图与JSON相同。 What I want to do is to collect the collections according to their id and create a collection.
我要做的是根据其ID收集集合并创建一个集合。 How can I do it?
我该怎么做?
A.json A.json
{
"_id" : ObjectId("58455d2d506c1cab1c82152c"),
"value" : 515835.0
}
{
"_id" : ObjectId("58455d2d506c1cab1c82153c"),
"value" : 6621696.0
}
B.json B.json
{
"_id" : ObjectId("58455d2d506c1cab1c82152c"),
"value" : 2118.0
}
{
"_id" : ObjectId("58455d2d506c1cab1c82153c"),
"value" : 1190.0
}
{
"_id" : ObjectId("423232d2d506c1cab1c1232c"),
"value" : 10.0
}
Collect in A collection, id: 1, collection B id: 1 if it matches. 在A集合中收集,ID:1,集合B ID:1(如果匹配)。
A in the collection, id: 2, if you are not in any collection, you are only showing that value. 集合ID中的A:2,如果您不在任何集合中,则仅显示该值。
In the last collection I have collected, I want to make a collection of objects and id in pairs. 在我收集的最后一个收集中,我想成对收集对象和ID。
Result.json Result.json
{
"_id" : ObjectId("58455d2d506c1cab1c82152c"),
"value" : 517953.0 // A.value + B.value
}
{
"_id" : ObjectId("58455d2d506c1cab1c82153c"),
"value" : 6633596.0 // A.value + B.value
}
{
"_id" : ObjectId("423232d2d506c1cab1c1232c"),
"value" : 10.0 // B.value (A.value : null)
}
i want this for multiple collections. 我想要这个为多个集合。
For 1-0/1 relation given in the example you can use $lookup as following: 对于示例中给出的1-0 / 1关系,可以使用$ lookup ,如下所示:
db.B.aggregate([
{$lookup: {
from: "A",
localField: "_id",
foreignField: "_id",
as: "a"
}},
{$unwind: {path: "$a", preserveNullAndEmptyArrays: true}},
{$project: {
value: {$add: ["$value", {$ifNull: ["$a.value", 0 ]}]}
}}
]);
It does ignore any documents in A, which have no corresponding documents in B, ie result have the same number of documents as in collection B. 它的确会忽略A中的任何文档,而B中没有相应的文档,即结果与集合B中的文档数量相同。
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