MongoDB 高级索引

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  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"
    }
  )
  

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  上面的文档包含一个address子文档和一个tags数组。
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  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
  }
  >
  

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  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"
  }
  
  

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  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.cainiaoya.com",
          "port" : 27017.0, 
          "version" : "4.4.0", 
          "gitVersion" : "563487e100c4215e2dce98d0af2a6a5a2d67c5cf"
      }, 
      "ok" : 1.0
  }
  

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  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
  }
  

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  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"
  }
  

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  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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