是否可以在MongoDB中存在于数组字段中的文档字段上创建索引？

如何解决是否可以在MongoDB中存在于数组字段中的文档字段上创建索引？

我在MongoDB中有这样的文档：

{ 
  "item" : "I1","Price" : 
      [
          {"d": "2020-07-01","t":t1,"v":1000},{"d": "2020-07-01","t":t2,"v":1500},"t":t3,"v":1350},...                     
      ] 
 },{ 
   "item" : "I2","Price" :
      [
          {"d": "2020-07-01","v":1025},{"d": "2020-07-02","v":1050},...
      ]
 }

我只是想知道是否可以在“ Price.d”上创建索引？ 谢谢

解决方法

是的。

Referenece from the documentation

如果字段是文档数组，则可以为嵌入的字段建立索引以创建复合索引。例如，考虑一个包含以下文档的集合：

{ _id: 1,a: [ { x: 5,z: [ 1,2 ] },{ z: [ 1,2 ] } ] }
{ _id: 2,a: [ { x: 5 },{ z: 4 } ] }

您可以在 { "a.x": 1,"a.z": 1 }上创建一个复合索引。限制也适用于最多一个索引字段可以是数组的限制。

,

是的，您可以举一个例子。代码。

--from mongo shell,windows:
//prepare data
> db.test11.find().pretty();
{
        "_id" : ObjectId("5f47c775c42d78fc841f35c5"),"item" : "I1","Price" : [
                {
                        "d" : "2020-07-01","t" : 1,"v" : 1000
                },{
                        "d" : "2020-07-01","t" : 2,"v" : 1500
                },"t" : 3,"v" : 1350
                }
        ]
}
{
        "_id" : ObjectId("5f47c775c42d78fc841f35c6"),"item" : "I2","v" : 1025
                },{
                        "d" : "2020-07-02","v" : 1050
                }
        ]
}
//create index and explain shows the index used
> db.test11.createIndex({"Price.d":1})
{
        "createdCollectionAutomatically" : false,"numIndexesBefore" : 1,"numIndexesAfter" : 2,"ok" : 1
}
> db.test11.getIndexes();
[
        {
                "v" : 2,"key" : {
                        "_id" : 1
                },"name" : "_id_","ns" : "mycustomers.test11"
        },{
                "v" : 2,"key" : {
                        "Price.d" : 1
                },"name" : "Price.d_1","ns" : "mycustomers.test11"
        }
]
> db.test11.find({"Price.d": "2020-07-02"});
{ "_id" : ObjectId("5f47c775c42d78fc841f35c6"),"Price" : [ { "d" : "2020-07-01","v" : 1025 },{ "d" : "2020-07-02","v" : 1050 } ] }
> db.test11.find({"Price.d": "2020-07-02"}).explain();
{
        "queryPlanner" : {
                "plannerVersion" : 1,"namespace" : "mycustomers.test11","indexFilterSet" : false,"parsedQuery" : {
                        "Price.d" : {
                                "$eq" : "2020-07-02"
                        }
                },"queryHash" : "F5F98F8D","planCacheKey" : "B39E1D2D","winningPlan" : {
                        "stage" : "FETCH","inputStage" : {
                                "stage" : "IXSCAN","keyPattern" : {
                                        "Price.d" : 1
                                },"indexName" : "Price.d_1","isMultiKey" : true,"multiKeyPaths" : {
                                        "Price.d" : [
                                                "Price"
                                        ]
                                },"isUnique" : false,"isSparse" : false,"isPartial" : false,"indexVersion" : 2,"direction" : "forward","indexBounds" : {
                                        "Price.d" : [
                                                "[\"2020-07-02\",\"2020-07-02\"]"
                                        ]
                                }
                        }
                },"rejectedPlans" : [ ]
        },},"ok" : 1
}
>