MongoDB如何索引数组？

Posted 2023-02-23

【中文标题】MongoDB如何索引数组？

【英文标题】：How does MongoDB index arrays?

【发布时间】：2011-05-02 19:52:30

【问题描述】：

在 MongoDB 中，如果我要在字段 "color" 中存储一个数组（例如 ["red", "blue"]），它会索引 "red" 和 "blue"，以便我可以查询 "red"，例如，还是是否将"red", "blue" 设为复合索引？

【参考方案1】：

在索引数组时，MongoDB 会索引数组的每个值，以便您可以查询单个项目，例如“红色”。例如：

> db.col1.save('colors': ['red','blue'])
> db.col1.ensureIndex('colors':1)

> db.col1.find('colors': 'red')
 "_id" : ObjectId("4ccc78f97cf9bdc2a2e54ee9"), "colors" : [ "red", "blue" ] 
> db.col1.find('colors': 'blue')
 "_id" : ObjectId("4ccc78f97cf9bdc2a2e54ee9"), "colors" : [ "red", "blue" ] 

有关更多信息，请查看 MongoDB 关于 Multikeys 的文档：http://www.mongodb.org/display/DOCS/Multikeys

【讨论】：

是否可以搜索部分数组，例如 ("colors" : [ "red", "blue" , "green"])，我可以搜索 ("colors" : [ "red", "blue" ]) 还是我必须单独做？

@GauravAbbi - 我认为这可行，但 mongo 只会使用索引来查找第一个数组键。之后，它会扫描该组文档以查找与其余键匹配的文档。

将多键索引与复合索引相对应的注意事项。例如描述主要颜色和次要颜色的索引？

@GauravAbbi ：我认为你应该做一个“颜色”：$in:["red", "blue"]。

【参考方案2】：

您可以通过在查询中附加“解释”来简单地测试索引使用情况：

> db.col1.save('colors': ['red','blue'])

# without index
> db.col1.find('colors': 'red').explain()

        "queryPlanner" : 
                "plannerVersion" : 1,
                "namespace" : "protrain.col1",
                "indexFilterSet" : false,
                "parsedQuery" : 
                        "colors" : 
                                "$eq" : "red"
                        
                ,
                "winningPlan" : 
                        "stage" : "COLLSCAN", <--- simple column scan
                        "filter" : 
                                "colors" : 
                                        "$eq" : "red"
                                
                        ,
                        "direction" : "forward"
                ,
                "rejectedPlans" : [ ]
        ,
        "serverInfo" : 
                "host" : "bee34f15fe28",
                "port" : 27017,
                "version" : "3.4.4",
                "gitVersion" : "888390515874a9debd1b6c5d36559ca86b44babd"
        ,
        "ok" : 1


# query with index
> db.col1.createIndex(  "colors":1  )
> db.col1.find('colors': 'red').explain()

        "queryPlanner" : 
                "plannerVersion" : 1,
                "namespace" : "protrain.col1",
                "indexFilterSet" : false,
                "parsedQuery" : 
                        "colors" : 
                                "$eq" : "red"
                        
                ,
                "winningPlan" : 
                        "stage" : "FETCH",
                        "inputStage" : 
                                "stage" : "IXSCAN", <!---- INDEX HAS BEEN USED
                                "keyPattern" : 
                                        "colors" : 1
                                ,
                                "indexName" : "colors_1",
                                "isMultiKey" : true,
                                "multiKeyPaths" : 
                                        "colors" : [
                                                "colors"
                                        ]
                                ,
                                "isUnique" : false,
                                "isSparse" : false,
                                "isPartial" : false,
                                "indexVersion" : 2,
                                "direction" : "forward",
                                "indexBounds" : 
                                        "colors" : [
                                                "[\"red\", \"red\"]"
                                        ]
                                
                        
                ,
                "rejectedPlans" : [ ]
        ,
        "serverInfo" : 
                "host" : "bee34f15fe28",
                "port" : 27017,
                "version" : "3.4.4",
                "gitVersion" : "888390515874a9debd1b6c5d36559ca86b44babd"
        ,
        "ok" : 1

对于具有结构化索引的结构，您可以使用数组位置来索引数组内的字段：

    '_id': 'BB167E2D61909E848EBC96C7B33251AC',
    'hist': 
        'map': 
            '10': 1
        
    ,
    'wayPoints': [
        'bhf_name': 'Zinsgutstr.(Berlin)',
        'ext_no': 900180542,
        'lat': 52.435158,
        'lon': 13.559086,
        'puic': 86,
        'time': 
            'dateTime': '2018-01-10T09: 38: 00',
            'offset': 
                'totalSeconds': 3600
            
        ,
        'train_name': 'Bus162'
    ,
    
        'bhf_name': 'SAdlershof(Berlin)',
        'ext_no': 900193002,
        'lat': 52.435104,
        'lon': 13.54055,
        'puic': 86,
        'time': 
            'dateTime': '2018-01-10T09: 44: 00',
            'offset': 
                'totalSeconds': 3600
            
        ,
        'train_name': 'Bus162'
    ]



db.col.createIndex(  "wayPoints.0.ext_no":1  )
db.col.createIndex(  "wayPoints.0.train_name":1  )
db.col.createIndex(  "wayPoints.1.ext_no":1  )
db.col.createIndex(  "wayPoints.1.train_name":1  )

> db.col.find(
... 
...  "wayPoints.ext_no": 900180542
... 
... ,
...     
...         "wayPoints.ext_no":1,
...         "wayPoints.train_name":1,
...         "wayPoints.time":1
...     
... ).explain()

        "queryPlanner" : 
                "plannerVersion" : 1,
                "namespace" : "db.col",
                "indexFilterSet" : false,
                "parsedQuery" : 
                        "wayPoints.ext_no" : 
                                "$eq" : 900180542
                        
                ,
                "winningPlan" : 
                        "stage" : "PROJECTION",
                        "transformBy" : 
                                "wayPoints.ext_no" : 1,
                                "wayPoints.train_name" : 1,
                                "wayPoints.time" : 1
                        ,
                        "inputStage" : 
                                "stage" : "FETCH",
                                "inputStage" : 
                                        "stage" : "IXSCAN",
                                        "keyPattern" : 
                                                "wayPoints.ext_no" : 1
                                        ,
                                        "indexName" : "wayPoints.ext_no_1",
                                        "isMultiKey" : true,
                                        "multiKeyPaths" : 
                                                "wayPoints.ext_no" : [
                                                        "wayPoints"
                                                ]
                                        ,
                                        "isUnique" : false,
                                        "isSparse" : false,
                                        "isPartial" : false,
                                        "indexVersion" : 2,
                                        "direction" : "forward",
                                        "indexBounds" : 
                                                "wayPoints.ext_no" : [
                                                        "[900180542.0, 900180542.0]"
                                                ]
                                        
                                
                        
                ,
                "rejectedPlans" : [ ]
        ,
        "serverInfo" : 
                "host" : "bee34f15fe28",
                "port" : 27017,
                "version" : "3.4.4",
                "gitVersion" : "888390515874a9debd1b6c5d36559ca86b44babd"
        ,
        "ok" : 1