限制跳過排序並計算 find() 方法的結果
與 find()
方法的聚合方法類似,你可以限制,跳過,排序和計算結果。假設我們有以下收藏:
db.test.insertMany([
{name:"Any", age:"21", status:"busy"},
{name:"Tony", age:"25", status:"busy"},
{name:"Bobby", age:"28", status:"online"},
{name:"Sonny", age:"28", status:"away"},
{name:"Cher", age:"20", status:"online"}
])
列出集合:
db.test.find({})
將返回:
{ "_id" : ObjectId("592516d7fbd5b591f53237b0"), "name" : "Any", "age" : "21", "status" : "busy" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b1"), "name" : "Tony", "age" : "25", "status" : "busy" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b2"), "name" : "Bobby", "age" : "28", "status" : "online" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b3"), "name" : "Sonny", "age" : "28", "status" : "away" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b4"), "name" : "Cher", "age" : "20", "status" : "online" }
要跳過前 3 個檔案:
db.test.find({}).skip(3)
將返回:
{ "_id" : ObjectId("592516d7fbd5b591f53237b3"), "name" : "Sonny", "age" : "28", "status" : "away" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b4"), "name" : "Cher", "age" : "20", "status" : "online" }
要按欄位名稱降序排序:
db.test.find({}).sort({ "name" : -1})
將返回:
{ "_id" : ObjectId("592516d7fbd5b591f53237b1"), "name" : "Tony", "age" : "25", "status" : "busy" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b3"), "name" : "Sonny", "age" : "28", "status" : "away" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b4"), "name" : "Cher", "age" : "20", "status" : "online" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b2"), "name" : "Bobby", "age" : "28", "status" : "online" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b0"), "name" : "Any", "age" : "21", "status" : "busy" }
如果要對升序進行排序,只需將 -1 替換為 1 即可
要計算結果:
db.test.find({}).count()
將返回:
5
也允許這種方法的組合。例如,從降序排序的集合中獲取 2 個文件,跳過第一個 1:
db.test.find({}).sort({ "name" : -1}).skip(1).limit(2)
將返回:
{ "_id" : ObjectId("592516d7fbd5b591f53237b3"), "name" : "Sonny", "age" : "28", "status" : "away" }
{ "_id" : ObjectId("592516d7fbd5b591f53237b4"), "name" : "Cher", "age" : "20", "status" : "online" }