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从MongoDB find()结果集中确定最后一个文档？

2024-04-24 00:41:15 511

要从MongoDBfind()结果集中识别最后一个文档，可以sort()按降序使用。语法如下-

db.yourCollectionName.find().sort( { _id : -1 } ).limit(1).pretty();

为了理解上述语法，让我们用文档创建一个集合。使用文档创建集合的查询如下-

> db.identifyLastDocuementDemo.insertOne({"UserName":"Larry","UserAge":24,"UserCountryName":"US"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c94a2ff4cf1f7a64fa4df57")
}
> db.identifyLastDocuementDemo.insertOne({"UserName":"Chris","UserAge":21,"UserCountryName":"UK"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c94a3094cf1f7a64fa4df58")
}
> db.identifyLastDocuementDemo.insertOne({"UserName":"David","UserAge":25,"UserCountryName":"AUS"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c94a3174cf1f7a64fa4df59")
}
> db.identifyLastDocuementDemo.insertOne({"UserName":"Sam","UserAge":26,"UserCountryName":"US"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c94a3224cf1f7a64fa4df5a")
}
> db.identifyLastDocuementDemo.insertOne({"UserName":"Mike","UserAge":27,"UserCountryName":"AUS"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c94a32e4cf1f7a64fa4df5b")
}
> db.identifyLastDocuementDemo.insertOne({"UserName":"Carol","UserAge":28,"UserCountryName":"UK"});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5c94a33c4cf1f7a64fa4df5c")
}

在find()method的帮助下显示集合中的所有文档。查询如下-

> db.identifyLastDocuementDemo.find().pretty();

以下是输出-

{
   "_id" : ObjectId("5c94a2ff4cf1f7a64fa4df57"),
   "UserName" : "Larry",
   "UserAge" : 24,
   "UserCountryName" : "US"
}
{
   "_id" : ObjectId("5c94a3094cf1f7a64fa4df58"),
   "UserName" : "Chris",
   "UserAge" : 21,
   "UserCountryName" : "UK"
}
{
   "_id" : ObjectId("5c94a3174cf1f7a64fa4df59"),
   "UserName" : "David",
   "UserAge" : 25,
   "UserCountryName" : "AUS"
}
{
   "_id" : ObjectId("5c94a3224cf1f7a64fa4df5a"),
   "UserName" : "Sam",
   "UserAge" : 26,
   "UserCountryName" : "US"
}
{
   "_id" : ObjectId("5c94a32e4cf1f7a64fa4df5b"),
   "UserName" : "Mike",
   "UserAge" : 27,
   "UserCountryName" : "AUS"
}
{
   "_id" : ObjectId("5c94a33c4cf1f7a64fa4df5c"),
   "UserName" : "Carol",
   "UserAge" : 28,
   "UserCountryName" : "UK"
}

这是从MongoDBfind()结果集中识别最后一个文档的查询-

> db.identifyLastDocuementDemo.find().sort( { _id : -1 } ).limit(1).pretty();

以下是输出-

{
   "_id" : ObjectId("5c94a33c4cf1f7a64fa4df5c"),
   "UserName" : "Carol",
   "UserAge" : 28,
   "UserCountryName" : "UK"
}

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从MongoDB find()结果集中确定最后一个文档？

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