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如何獲取與查詢匹配的所有嵌入文檔?作爲文檔說:
的位置$操作者限制的數組的內容從 查詢結果到僅包含第一元件匹配查詢 文檔。
例子:
{ "_id" : 7, semester: 3, "grades" : [ { grade: 80, mean: 75, std: 8 },
{ grade: 85, mean: 90, std: 5 },
{ grade: 90, mean: 85, std: 3 } ] }
{ "_id" : 8, semester: 3, "grades" : [ { grade: 92, mean: 88, std: 8 },
{ grade: 78, mean: 90, std: 5 },
{ grade: 88, mean: 85, std: 3 } ] }
例如,我需要的成績,只有std < 8
,運營商$返回第一個匹配的結果,所以我們有兩個目標:
{ grade: 85, mean: 90, std: 5 }
{ grade: 78, mean: 90, std: 5 }
,但結果是我需要:
{ grade: 85, mean: 90, std: 5 },
{ grade: 90, mean: 85, std: 3 }
{ grade: 78, mean: 90, std: 5 },
{ grade: 88, mean: 85, std: 3 }