MongoDB - Cursors
2015-12-09 16:39 abce 阅读(619) 评论(0) 编辑 收藏 举报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。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | > 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:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | > var myCursor = db.users.find();< br >> 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 > |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 | > var myCursor = db.users.find();< br >> while(myCursor.hasNext()){print(tojson(myCursor.next()));}< br >{ "_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" } > |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 | > 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" } > |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 | > 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
1 2 3 4 5 6 7 8 9 10 11 | > 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])
1 2 3 4 5 6 7 8 9 10 | > 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:
1 | var myCursor = db.users.find().addOption(DBQuery.Option.noTimeout); |
记得要及时关闭游标!
【推荐】国内首个AI IDE,深度理解中文开发场景,立即下载体验Trae
【推荐】编程新体验,更懂你的AI,立即体验豆包MarsCode编程助手
【推荐】抖音旗下AI助手豆包,你的智能百科全书,全免费不限次数
【推荐】轻量又高性能的 SSH 工具 IShell:AI 加持,快人一步
· AI与.NET技术实操系列(二):开始使用ML.NET
· 记一次.NET内存居高不下排查解决与启示
· 探究高空视频全景AR技术的实现原理
· 理解Rust引用及其生命周期标识(上)
· 浏览器原生「磁吸」效果!Anchor Positioning 锚点定位神器解析
· DeepSeek 开源周回顾「GitHub 热点速览」
· 物流快递公司核心技术能力-地址解析分单基础技术分享
· .NET 10首个预览版发布:重大改进与新特性概览!
· AI与.NET技术实操系列(二):开始使用ML.NET
· .NET10 - 预览版1新功能体验(一)