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"
}