有没有一种方法可以限制某个MongoDB集合中的记录数？
是的，您可以将上限参数与上限参数一起使用。以下是语法-
db.createCollection("yourCollectionName",{capped:true,size:yourSizeInBytes,max:howManyRecordsYouWant})让我们首先创建一个带有capped：true的集合：
> db.createCollection("limitTheNumberOfRecordsDemo",{capped:true,size:200024,max:3})
{ "ok" : 1 }我们现在将创建包含文档的集合-
> db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"James Brown"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9e601b50a6c6dd317adad")
}
> db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"Sam Williams"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9e60bb50a6c6dd317adae")
}
> db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"David Miller"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9e612b50a6c6dd317adaf")
}
> db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"Carol Taylor"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9e61ab50a6c6dd317adb0")
}
> db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"Adam Smith"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9e649b50a6c6dd317adb1")
}
> db.limitTheNumberOfRecordsDemo.insertOne({"ClientName":"John Doe"});
{
"acknowledged" : true,
"insertedId" : ObjectId("5cd9e64fb50a6c6dd317adb2")
}以下是在find()method的帮助下显示集合中所有文档的查询。在这里，您从上述集合中仅获得3条记录，因为我们将上限设置为：
> db.limitTheNumberOfRecordsDemo.find();
这将产生以下输出-
{ "_id" : ObjectId("5cd9e61ab50a6c6dd317adb0"), "ClientName" : "Carol Taylor" }
{ "_id" : ObjectId("5cd9e649b50a6c6dd317adb1"), "ClientName" : "Adam Smith" }
{ "_id" : ObjectId("5cd9e64fb50a6c6dd317adb2"), "ClientName" : "John Doe" }