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  MongoDB 高级索引

  • 高级索引

    我们已将以下文档插入名为用户的集合中，如下所示- 
    
db.users.insert(
  {
    "address": {
      "city": "Los Angeles",
      "state": "California",
      "pincode": "123"
    },
    "tags": [
      "music",
      "cricket",
      "blogs"
    ],
    "name": "Tom Benzamin"
  }
)
    上面的文档包含一个address子文档和一个tags数组。

  • 索引数组字段

    假设我们要根据用户的标签搜索用户文档。为此，我们将在集合中的标签数组上创建索引。依次在数组上创建索引将为其每个字段创建单独的索引条目。因此，在本例中，当我们在标签数组上创建索引时，将为其音乐，板球和博客的值创建单独的索引。要在标签数组上创建索引，请使用以下代码- 
    
>db.users.createIndex({"tags":1})
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 2,
"numIndexesAfter" : 3,
"ok" : 1
}
>
    创建索引后，我们可以像这样搜索集合的标签字段- 
    
> db.users.find({tags:"cricket"}).pretty()
{ 
    "_id" : ObjectId("5f4f079c40ea6da6414f2bd1"), 
    "address" : {
        "city" : "Los Angeles", 
        "state" : "California", 
        "pincode" : "123"
    }, 
    "tags" : [
        "music", 
        "cricket", 
        "blogs"
    ], 
    "name" : "Tom Benzamin"
}
    要验证是否使用了正确的索引编制，请使用以下explain命令- 
    
> db.users.find({tags:"cricket"}).explain()
{ 
    "queryPlanner" : {
        "plannerVersion" : 1.0, 
        "namespace" : "test.users", 
        "indexFilterSet" : false, 
        "parsedQuery" : {
            "tags" : {
                "$eq" : "cricket"
            }
        }, 
        "queryHash" : "9D3B61A7", 
        "planCacheKey" : "04C9997B", 
        "winningPlan" : {
            "stage" : "FETCH", 
            "inputStage" : {
                "stage" : "IXSCAN", 
                "keyPattern" : {
                    "tags" : 1.0
                }, 
                "indexName" : "tags_1", 
                "isMultiKey" : true, 
                "multiKeyPaths" : {
                    "tags" : [
                        "tags"
                    ]
                }, 
                "isUnique" : false, 
                "isSparse" : false, 
                "isPartial" : false, 
                "indexVersion" : 2.0, 
                "direction" : "forward", 
                "indexBounds" : {
                    "tags" : [
                        "[\"cricket\", \"cricket\"]"
                    ]
                }
            }
        }, 
        "rejectedPlans" : [

        ]
    }, 
    "serverInfo" : {
        "host" : "www.jc2182.com", 
        "port" : 27017.0, 
        "version" : "4.4.0", 
        "gitVersion" : "563487e100c4215e2dce98d0af2a6a5a2d67c5cf"
    }, 
    "ok" : 1.0
}

  • 索引子文档字段

    假设我们要根据城市，州和密码字段搜索文档。由于所有这些字段都是地址子文档字段的一部分，因此我们将在子文档的所有字段上创建索引。要在子文档的所有三个字段上创建索引，请使用以下代码- 
    
>db.users.createIndex({"address.city":1,"address.state":1,"address.pincode":1})
{ 
    "createdCollectionAutomatically" : false, 
    "numIndexesBefore" : 2.0, 
    "numIndexesAfter" : 3.0, 
    "ok" : 1.0
}
    创建索引后，我们可以使用该索引搜索任何子文档字段，如下所示： 
    
> db.users.find({"address.city":"Los Angeles"}).pretty()
{ 
    "_id" : ObjectId("5f4f079c40ea6da6414f2bd1"), 
    "address" : {
        "city" : "Los Angeles", 
        "state" : "California", 
        "pincode" : "123"
    }, 
    "tags" : [
        "music", 
        "cricket", 
        "blogs"
    ], 
    "name" : "Tom Benzamin"
}
    请记住，查询表达式必须遵循指定索引的顺序。因此，上面创建的索引将支持以下查询- 
    
db.users.find({"address.city":"Los Angeles","address.state":"California"}).pretty()
{ 
    "_id" : ObjectId("5f4f079c40ea6da6414f2bd1"), 
    "address" : {
        "city" : "Los Angeles", 
        "state" : "California", 
        "pincode" : "123"
    }, 
    "tags" : [
        "music", 
        "cricket", 
        "blogs"
    ], 
    "name" : "Tom Benzamin"
}
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