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法律研究從MongoDB中獲取隨機記錄嗎？
要從MongoDB中獲得隨機記錄，可以使用聚合函式。語法如下
db.yourCollectionName.aggregate([{$sample:{size:1}}]);為了理解以上語法，讓我們建立一個帶有一些文件的集合。建立集合的查詢如下
>db.employeeInformation.insert({"EmployeeId":1,"EmployeeName":"Maxwell","EmployeeAge":26});
WriteResult({ "nInserted" : 1 })
>db.employeeInformation.insert({"EmployeeId":2,"EmployeeName":"David","EmployeeAge":25});
WriteResult({ "nInserted" : 1 })
>db.employeeInformation.insert({"EmployeeId":3,"EmployeeName":"Carol","EmployeeAge":24});
WriteResult({ "nInserted" : 1 })
>db.employeeInformation.insert({"EmployeeId":4,"EmployeeName":"Bob","EmployeeAge":28});
WriteResult({ "nInserted" : 1 })
>db.employeeInformation.insert({"EmployeeId":5,"EmployeeName":"Sam","EmployeeAge":27);
WriteResult({ "nInserted" : 1 })現在，您可以藉助find()方法顯示集合中的所有文件。該查詢如下
> db.employeeInformation.find().pretty();
輸出如下
{
"_id" : ObjectId("5c6d3079734e98fc0a434ae5"),
"EmployeeId" : 1,
"EmployeeName" : "Maxwell",
"EmployeeAge" : 26
}
{
"_id" : ObjectId("5c6d308c734e98fc0a434ae6"),
"EmployeeId" : 2,
"EmployeeName" : "David",
"EmployeeAge" : 25
}
{
"_id" : ObjectId("5c6d309d734e98fc0a434ae7"),
"EmployeeId" : 3,
"EmployeeName" : "Carol",
"EmployeeAge" : 24
}
{
"_id" : ObjectId("5c6d30ab734e98fc0a434ae8"),
"EmployeeId" : 4,
"EmployeeName" : "Bob",
"EmployeeAge" : 28
}
{
"_id" : ObjectId("5c6d30bb734e98fc0a434ae9"),
"EmployeeId" : 5,
"EmployeeName" : "Sam",
"EmployeeAge" : 27
}以下是獲取隨機記錄的查詢
> db.employeeInformation.aggregate([{$sample:{size:1}}]).pretty();輸出如下
{
"_id" : ObjectId("5c6d30bb734e98fc0a434ae9"),
"EmployeeId" : 5,
"EmployeeName" : "Sam",
"EmployeeAge" : 27
}讓我們使用相同的查詢獲取另一條隨機記錄
> db.employeeInformation.aggregate([{$sample:{size:1}}]).pretty();輸出如下
{
"_id" : ObjectId("5c6d308c734e98fc0a434ae6"),
"EmployeeId" : 2,
"EmployeeName" : "David",
"EmployeeAge" : 25
}
更新於： 2019 年 7 月 30 日
1K+ 次瀏覽
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