如何在MongoDB中的单个集合中的文档之间执行集合的交集？
您可以为此使用$setIntersection。首先让我们创建一个包含文档的集合-
> db.setInterSectionDemo.insertOne(
... {"_id":101, "Value1":[55,67,89]}
... );
{ "acknowledged" : true, "insertedId" : 101 }
> db.setInterSectionDemo.insertOne(
... {"_id":102, "Value2":[90,45,55]}
... );
{ "acknowledged" : true, "insertedId" : 102 }
> db.setInterSectionDemo.insertOne(
... {"_id":103, "Value3":[92,67,45]}
... );
{ "acknowledged" : true, "insertedId" : 103 }以下是在find()方法的帮助下显示集合中所有文档的查询-
> db.setInterSectionDemo.find().pretty();
这将产生以下输出-
{ "_id" : 101, "Value1" : [ 55, 67, 89 ] }
{ "_id" : 102, "Value2" : [ 90, 45, 55 ] }
{ "_id" : 103, "Value3" : [ 92, 67, 45 ]这是在MongoDB中的单个集合中查找文档之间的集合交集的查询-
> db.setInterSectionDemo.aggregate([
... {
... "$match": {
... "_id": { "$in": [101, 103] }
... }
... },
... {
... "$group": {
... "_id": 0,
... "firstValue": { "$first": "$Value1" },
... "secondValue": { "$last": "$Value3" }
... }
... },
... {
... "$project": {
... "firstValue": 1,
... "secondValue": 1,
... "CommonValue": { "$setIntersection": [ "$firstValue", "$secondValue" ] },
... "_id": 0
... }
... }
... ]);这将产生以下输出-
{ "firstValue" : [ 55, 67, 89 ], "secondValue" : [ 92, 67, 45 ], "CommonValue" : [ 67 ] }