我正在学习MongoDB自己，我发现自己在一个奇怪的情况。这是查询#1
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当我运行
db.players.find({$or: [{"position":"Left Wing"}, {"position":"Right Wing"}]}).pretty()时，在我的样本数据集上，这是结果:"_id" : ObjectId("57d9a212698d3e0bd0f5a245"), "position" : "Right Wing", "id" : 8465166, "weight" : 200, "height" : "6' 0"", "imageUrl" : "http://1.cdn.nhle.com/photos/mugs/8465166.jpg", "birthplace" : "Seria, BRN", "age" : 37, "name" : "Craig Adams", "birthdate" : "April 26, 1977", "number" : 27 "_id" : ObjectId("57d9a212698d3e0bd0f5a246"), "position" : "Right Wing", "id" : 8475761, "weight" : 195, "height" : "6' 2"", "imageUrl" : "http://1.cdn.nhle.com/photos/mugs/8475761.jpg", "birthplace" : "Gardena, CA, USA", "age" : 23, "name" : "Beau Bennett", "birthdate" : "November 27, 1991", "number" : 19 "_id" : ObjectId("57d9a212698d3e0bd0f5a247"), "position" : "Left Wing", "id" : 8471260, "weight" : 202, "height" : "6' 1"", "imageUrl" : "http://3.cdn.nhle.com/photos/mugs/8471260.jpg", "birthplace" : "Meadow Lake, SK, CAN", "age" : 29, "name" : "Blake Comeau", "birthdate" : "February 18, 1986", "number" : 17 "_id" : ObjectId("57d9a212698d3e0bd0f5a249"), "position" : "Right Wing", "id" : 8471703, "twitterURL" : "https://twitter.com/S9Downie", "weight" : 191, "height" : "5' 11"", "imageUrl" : "http://1.cdn.nhle.com/photos/mugs/8471703.jpg", "birthplace" : "Newmarket, ON, CAN", "twitterHandle" : "S9Downie", "age" : 28, "name" : "Steve Downie", "birthdate" : "April 03, 1987", "number" : 23 "_id" : ObjectId("57d9a212698d3e0bd0f5a24a"), "position" : "Right Wing", "id" : 8466393, "weight" : 205, "height" : "6' 1"", "imageUrl" : "http://2.cdn.nhle.com/photos/mugs/8466393.jpg", "birthplace" : "Laval, QC, CAN", "age" : 35, "name" : "Pascal Dupuis", "birthdate" : "April 07, 1979", "number" : 9 "_id" : ObjectId("57d9a212698d3e0bd0f5a24b"), "position" : "Right Wing", "id" : 8471887, "weight" : 189, "height" : "5' 11"", "imageUrl" : "http://1.cdn.nhle.com/photos/mugs/8471887.jpg", "birthplace" : "Sollentuna, SWE", "age" : 28, "name" : "Patric Hornqvist", "birthdate" : "January 01, 1987", "number" : 72 "_id" : ObjectId("57d9a212698d3e0bd0f5a24c"), "position" : "Left Wing", "id" : 8470543, "weight" : 195, "height" : "6' 0"", "imageUrl" : "http://3.cdn.nhle.com/photos/mugs/8470543.jpg", "birthplace" : "Regina, SK, CAN", "age" : 35, "name" : "Chris Kunitz", "birthdate" : "September 26, 1979", "number" : 14 "_id" : ObjectId("57d9a212698d3e0bd0f5a24f"), "position" : "Left Wing", "id" : 8474102, "twitterURL" : "https://twitter.com/DP_57", "weight" : 200, "height" : "6' 0"", "imageUrl" : "http://3.cdn.nhle.com/nhl/en/v3/photos/mugs/8474102.jpg", "birthplace" : "Sherbrooke, QC, CAN", "twitterHandle" : "DP_57", "age" : 26, "name" : "David Perron", "birthdate" : "May 28, 1988", "number" : 39对不起，格式化JSON文件很困难。
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当我运行
db.players.find({"position":"Left Wing"} || {"position":"Right Wing"}).pretty(),的结果是:"_id" : ObjectId("57d9a212698d3e0bd0f5a247"), "position" : "Left Wing", "id" : 8471260, "weight" : 202, "height" : "6' 1"", "imageUrl" : "http://3.cdn.nhle.com/photos/mugs/8471260.jpg", "birthplace" : "Meadow Lake, SK, CAN", "age" : 29, "name" : "Blake Comeau", "birthdate" : "February 18, 1986", "number" : 17 "_id" : ObjectId("57d9a212698d3e0bd0f5a24c"), "position" : "Left Wing", "id" : 8470543, "weight" : 195, "height" : "6' 0"", "imageUrl" : "http://3.cdn.nhle.com/photos/mugs/8470543.jpg", "birthplace" : "Regina, SK, CAN", "age" : 35, "name" : "Chris Kunitz", "birthdate" : "September 26, 1979", "number" : 14 "_id" : ObjectId("57d9a212698d3e0bd0f5a24f"), "position" : "Left Wing", "id" : 8474102, "twitterURL" : "https://twitter.com/DP_57", "weight" : 200, "height" : "6' 0"", "imageUrl" : "http://3.cdn.nhle.com/nhl/en/v3/photos/mugs/8474102.jpg", "birthplace" : "Sherbrooke, QC, CAN", "twitterHandle" : "DP_57", "age" : 26, "name" : "David Perron", "birthdate" : "May 28, 1988", "number" : 39
考虑到它们都是OR操作，为什么会有这种差异?请帮我理解一下。
Windows 10/MongoDB on IntelliJ
根据我的理解，对蒙古知之甚少。
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|| operator命令的工作方式如下
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a || b ->如果a为真，则只将值a传递给db.players.find(a)并忽略b。
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这里'a'指的是获取{"position":"Left Wing"}，所以它只检索"Left Wing"文档。
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where as $or:为每个条件准备索引，并获取"Left Wing"one_answers"Right Wing"的组合结果。
在mongo shell上试试下面的命令，我想它会给你一些更好的想法。
> {$or: [(1==1), (2==1)]}
[ true, false ]
> (1==1) || (2==1)
true
> {$or: [(2==1), (1==1)]}
[ false, true ]
> (2==1) || (1==1)
true
希望有帮助。
谢谢,
Rana
{"position":"Left Wing"} || {"position":"Right Wing"}的参数是一个JavaScript表达式，计算结果为{"position":"Left Wing"}，因为该项为真。这就是你实际传递给find的内容，这就是为什么你在那个查询中只得到"Left Wing"文档的原因。
你可以在shell中看到:
> var query = {"position":"Left Wing"} || {"position":"Right Wing"}
> query
{ "position" : "Left Wing" }
但你也可以简化你的$or查询使用$in代替:
db.players.find({"position": {$in: ["Left Wing", "Right Wing"]}})