MongoDB - Cursors
2024-08-26 03:57:30
db.collection.find()查询集合会返回一个包含查到的文档的游标。在mongo shell中，如果没有定义一个变量来该游标的内容，默认会迭代返回20个文档。
> db.users.count();db.users.count();
26
> db.users.find();db.users.find();
{ "_id" : ObjectId("5667dbba614c1d1953bce9ba"), "name" : "yb1", "age" : 1, "status" : "A" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9bb"), "name" : "yb2", "age" : 2, "status" : "B" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9bc"), "name" : "yb3", "age" : 3, "status" : "C" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9bd"), "name" : "yb4", "age" : 4, "status" : "D" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9be"), "name" : "yb5", "age" : 5, "status" : "E" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9bf"), "name" : "yb6", "age" : 6, "status" : "F" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c0"), "name" : "yb7", "age" : 7, "status" : "G" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c1"), "name" : "yb8", "age" : 8, "status" : "H" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c2"), "name" : "yb9", "age" : 9, "status" : "I" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c3"), "name" : "yb10", "age" : 10, "status" : "J" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c4"), "name" : "yb11", "age" : 11, "status" : "K" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c5"), "name" : "yb12", "age" : 12, "status" : "L" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c6"), "name" : "yb13", "age" : 13, "status" : "M" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c7"), "name" : "yb14", "age" : 14, "status" : "N" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c8"), "name" : "yb15", "age" : 15, "status" : "O" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c9"), "name" : "yb16", "age" : 16, "status" : "P" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9ca"), "name" : "yb17", "age" : 17, "status" : "Q" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9cb"), "name" : "yb18", "age" : 18, "status" : "R" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9cc"), "name" : "yb19", "age" : 19, "status" : "S" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9cd"), "name" : "yb20", "age" : 20, "status" : "T" }
Type "it" for more
>
手动迭代游标：
> var myCursor = db.users.find();
> myCursor
{ "_id" : ObjectId("5667dbba614c1d1953bce9ba"), "name" : "yb1", "age" : 1, "status" : "A" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9bb"), "name" : "yb2", "age" : 2, "status" : "B" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9bc"), "name" : "yb3", "age" : 3, "status" : "C" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9bd"), "name" : "yb4", "age" : 4, "status" : "D" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9be"), "name" : "yb5", "age" : 5, "status" : "E" }
{ "_id" : ObjectId("5667dbba614c1d1953bce9bf"), "name" : "yb6", "age" : 6, "status" : "F" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c0"), "name" : "yb7", "age" : 7, "status" : "G" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c1"), "name" : "yb8", "age" : 8, "status" : "H" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c2"), "name" : "yb9", "age" : 9, "status" : "I" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c3"), "name" : "yb10", "age" : 10, "status" : "J" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c4"), "name" : "yb11", "age" : 11, "status" : "K" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c5"), "name" : "yb12", "age" : 12, "status" : "L" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c6"), "name" : "yb13", "age" : 13, "status" : "M" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c7"), "name" : "yb14", "age" : 14, "status" : "N" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c8"), "name" : "yb15", "age" : 15, "status" : "O" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9c9"), "name" : "yb16", "age" : 16, "status" : "P" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9ca"), "name" : "yb17", "age" : 17, "status" : "Q" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9cb"), "name" : "yb18", "age" : 18, "status" : "R" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9cc"), "name" : "yb19", "age" : 19, "status" : "S" }
{ "_id" : ObjectId("5667dbbb614c1d1953bce9cd"), "name" : "yb20", "age" : 20, "status" : "T" }
Type "it" for more
>
> var myCursor = db.users.find();
> while(myCursor.hasNext()){print(tojson(myCursor.next()));}
{
"_id" : ObjectId("5667dbba614c1d1953bce9ba"),
"name" : "yb1",
"age" : 1,
"status" : "A"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bb"),
"name" : "yb2",
"age" : 2,
"status" : "B"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bc"),
"name" : "yb3",
"age" : 3,
"status" : "C"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bd"),
"name" : "yb4",
"age" : 4,
"status" : "D"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9be"),
"name" : "yb5",
"age" : 5,
"status" : "E"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bf"),
"name" : "yb6",
"age" : 6,
"status" : "F"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c0"),
"name" : "yb7",
"age" : 7,
"status" : "G"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c1"),
"name" : "yb8",
"age" : 8,
"status" : "H"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c2"),
"name" : "yb9",
"age" : 9,
"status" : "I"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c3"),
"name" : "yb10",
"age" : 10,
"status" : "J"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c4"),
"name" : "yb11",
"age" : 11,
"status" : "K"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c5"),
"name" : "yb12",
"age" : 12,
"status" : "L"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c6"),
"name" : "yb13",
"age" : 13,
"status" : "M"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c7"),
"name" : "yb14",
"age" : 14,
"status" : "N"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c8"),
"name" : "yb15",
"age" : 15,
"status" : "O"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c9"),
"name" : "yb16",
"age" : 16,
"status" : "P"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9ca"),
"name" : "yb17",
"age" : 17,
"status" : "Q"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cb"),
"name" : "yb18",
"age" : 18,
"status" : "R"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cc"),
"name" : "yb19",
"age" : 19,
"status" : "S"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cd"),
"name" : "yb20",
"age" : 20,
"status" : "T"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9ce"),
"name" : "yb21",
"age" : 21,
"status" : "U"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cf"),
"name" : "yb22",
"age" : 22,
"status" : "V"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d0"),
"name" : "yb23",
"age" : 23,
"status" : "W"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d1"),
"name" : "yb24",
"age" : 24,
"status" : "X"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d2"),
"name" : "yb25",
"age" : 25,
"status" : "Y"
}
{
"_id" : ObjectId("5667dbbc614c1d1953bce9d3"),
"name" : "yb26",
"age" : 26,
"status" : "Z"
}
>
> var myCursor = db.users.find();
> while(myCursor.hasNext()){printjson(myCursor.next());}
{
"_id" : ObjectId("5667dbba614c1d1953bce9ba"),
"name" : "yb1",
"age" : 1,
"status" : "A"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bb"),
"name" : "yb2",
"age" : 2,
"status" : "B"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bc"),
"name" : "yb3",
"age" : 3,
"status" : "C"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bd"),
"name" : "yb4",
"age" : 4,
"status" : "D"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9be"),
"name" : "yb5",
"age" : 5,
"status" : "E"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bf"),
"name" : "yb6",
"age" : 6,
"status" : "F"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c0"),
"name" : "yb7",
"age" : 7,
"status" : "G"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c1"),
"name" : "yb8",
"age" : 8,
"status" : "H"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c2"),
"name" : "yb9",
"age" : 9,
"status" : "I"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c3"),
"name" : "yb10",
"age" : 10,
"status" : "J"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c4"),
"name" : "yb11",
"age" : 11,
"status" : "K"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c5"),
"name" : "yb12",
"age" : 12,
"status" : "L"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c6"),
"name" : "yb13",
"age" : 13,
"status" : "M"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c7"),
"name" : "yb14",
"age" : 14,
"status" : "N"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c8"),
"name" : "yb15",
"age" : 15,
"status" : "O"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c9"),
"name" : "yb16",
"age" : 16,
"status" : "P"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9ca"),
"name" : "yb17",
"age" : 17,
"status" : "Q"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cb"),
"name" : "yb18",
"age" : 18,
"status" : "R"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cc"),
"name" : "yb19",
"age" : 19,
"status" : "S"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cd"),
"name" : "yb20",
"age" : 20,
"status" : "T"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9ce"),
"name" : "yb21",
"age" : 21,
"status" : "U"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cf"),
"name" : "yb22",
"age" : 22,
"status" : "V"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d0"),
"name" : "yb23",
"age" : 23,
"status" : "W"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d1"),
"name" : "yb24",
"age" : 24,
"status" : "X"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d2"),
"name" : "yb25",
"age" : 25,
"status" : "Y"
}
{
"_id" : ObjectId("5667dbbc614c1d1953bce9d3"),
"name" : "yb26",
"age" : 26,
"status" : "Z"
}
>
> var myCursor = db.users.find();
> myCursor.forEach(printjson);
{
"_id" : ObjectId("5667dbba614c1d1953bce9ba"),
"name" : "yb1",
"age" : 1,
"status" : "A"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bb"),
"name" : "yb2",
"age" : 2,
"status" : "B"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bc"),
"name" : "yb3",
"age" : 3,
"status" : "C"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bd"),
"name" : "yb4",
"age" : 4,
"status" : "D"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9be"),
"name" : "yb5",
"age" : 5,
"status" : "E"
}
{
"_id" : ObjectId("5667dbba614c1d1953bce9bf"),
"name" : "yb6",
"age" : 6,
"status" : "F"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c0"),
"name" : "yb7",
"age" : 7,
"status" : "G"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c1"),
"name" : "yb8",
"age" : 8,
"status" : "H"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c2"),
"name" : "yb9",
"age" : 9,
"status" : "I"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c3"),
"name" : "yb10",
"age" : 10,
"status" : "J"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c4"),
"name" : "yb11",
"age" : 11,
"status" : "K"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c5"),
"name" : "yb12",
"age" : 12,
"status" : "L"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c6"),
"name" : "yb13",
"age" : 13,
"status" : "M"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c7"),
"name" : "yb14",
"age" : 14,
"status" : "N"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c8"),
"name" : "yb15",
"age" : 15,
"status" : "O"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9c9"),
"name" : "yb16",
"age" : 16,
"status" : "P"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9ca"),
"name" : "yb17",
"age" : 17,
"status" : "Q"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cb"),
"name" : "yb18",
"age" : 18,
"status" : "R"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cc"),
"name" : "yb19",
"age" : 19,
"status" : "S"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cd"),
"name" : "yb20",
"age" : 20,
"status" : "T"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9ce"),
"name" : "yb21",
"age" : 21,
"status" : "U"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9cf"),
"name" : "yb22",
"age" : 22,
"status" : "V"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d0"),
"name" : "yb23",
"age" : 23,
"status" : "W"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d1"),
"name" : "yb24",
"age" : 24,
"status" : "X"
}
{
"_id" : ObjectId("5667dbbb614c1d1953bce9d2"),
"name" : "yb25",
"age" : 25,
"status" : "Y"
}
{
"_id" : ObjectId("5667dbbc614c1d1953bce9d3"),
"name" : "yb26",
"age" : 26,
"status" : "Z"
}
>
使用迭代器索引
在mongo shell中，可以使用toArray()方法来迭代游标，并以array的形式返回游标的内容
> var myCursor = db.users.find();
> var usersArray = myCursor.toArray();
> var myDocument = usersArray[3]
> myDocumentmyDocument
{
"_id" : ObjectId("5667dbba614c1d1953bce9bd"),
"name" : "yb4",
"age" : 4,
"status" : "D"
}
>
也可以直接在游标上加下标的方式，查看文档：(cursor[index])
> var myCursor =db.users.find();
> var myCursor =myCursor[3];
> myCursormyCursor
{
"_id" : ObjectId("5667dbba614c1d1953bce9bd"),
"name" : "yb4",
"age" : 4,
"status" : "D"
}
>
cursor[index]等价于cursor.toArray()[index]
缺省情况下，在会话处于非活跃状态10分钟后，或者客户端已经遍历了游标的内容，mongodb会自动关闭游标。
如果想修改超时时间，使用cursor的时候，可以使用cursor.addOption()来修改noTimeout标记：
var myCursor = db.users.find().addOption(DBQuery.Option.noTimeout);
记得要及时关闭游标！
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