限制MongoDB中集合中的文档数量？
要限制集合中文档的数量，请设置capped−true。自行设置尺寸。让我们创建一个包含文档的集合-
> db.createCollection( "demo683", { capped: true, size: 5 ,max:4} )
{ "ok" : 1 }
> db.demo683.insertOne({Value:100});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea468afa7e81adc6a0b394e")
}
> db.demo683.insertOne({Value:500});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea468b0a7e81adc6a0b394f")
}
> db.demo683.insertOne({Value:1000});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea468b1a7e81adc6a0b3950")
}
> db.demo683.insertOne({Value:400});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea468b2a7e81adc6a0b3951")
}
> db.demo683.insertOne({Value:800});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea468b3a7e81adc6a0b3952")
}
> db.demo683.insertOne({Value:700});
{
"acknowledged" : true,
"insertedId" : ObjectId("5ea468b4a7e81adc6a0b3953")
}在find()方法的帮助下显示集合中的所有文档-
> db.demo683.find();
这将产生以下输出-
{ "_id" : ObjectId("5ea468b1a7e81adc6a0b3950"), "Value" : 1000 }
{ "_id" : ObjectId("5ea468b2a7e81adc6a0b3951"), "Value" : 400 }
{ "_id" : ObjectId("5ea468b3a7e81adc6a0b3952"), "Value" : 800 }
{ "_id" : ObjectId("5ea468b4a7e81adc6a0b3953"), "Value" : 700 }