MongoDB查询以计算所有文档中的不同值？
为此，请在MongoDB中使用aggregate()。让我们创建一个包含文档的集合-
> db.demo718.insertOne(
... {
... "id":101,
... "details":
... {
... "OtherDetails": ["Chris", "Mike", "Sam"], "GroupName": ["Group-1"], "Info": []
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eaae25843417811278f5880")
}
> db.demo718.insertOne(
... {
... "id":102,
... "details":
... {
... "OtherDetails": ["Chris", "David"], "GroupName": ["Group-1"], "Info": []
... }
... }
... );
{
"acknowledged" : true,
"insertedId" : ObjectId("5eaae25943417811278f5881")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo718.find();
这将产生以下输出-
{ "_id" : ObjectId("5eaae25843417811278f5880"), "id" : 101, "details" : { "OtherDetails" : [ "Chris", "Mike", "Sam" ], "GroupName" : [ "Group-1" ], "Info" : [ ] } }
{ "_id" : ObjectId("5eaae25943417811278f5881"), "id" : 102, "details" : { "OtherDetails" : [ "Chris", "David" ], "GroupName" : [ "Group-1" ], "Info" : [ ] } }以下是查询以计算所有文档中不同值的查询-
> db.demo718.aggregate([
... {
... $unwind: "$details.GroupName"
... },
... {
... $match: {
... "details.GroupName": "Group-1"
... }
... },
... {
... $unwind: "$details.OtherDetails"
... },
... {
... $group: {
... _id: "$details.GroupName",
... OtherDetailsUnique: {
... $addToSet: "$details.OtherDetails"
... }
... }
... },
... {
... $project: {
... _id : 0,
... GROUP_NAME: "$_id",
... OtherDetailsUniqueCount: {
... $size: "$OtherDetailsUnique"
... }
... }
... }
... ])这将产生以下输出-
{ "GROUP_NAME" : "Group-1", "OtherDetailsUniqueCount" : 4 }