Question

假设我有以下一组文件：

{ "_id" : 1, "semester" : 1, "grades" : [ 70, 87, 90 ] }
{ "_id" : 2, "semester" : 1, "grades" : [ 90, 88, 92 ] }
{ "_id" : 3, "semester" : 1, "grades" : [ 85, 100, 90 ] }
{ "_id" : 4, "semester" : 2, "grades" : [ 79, 85, 80 ] }
{ "_id" : 5, "semester" : 2, "grades" : [ 88, 88, 92 ] }
{ "_id" : 6, "semester" : 2, "grades" : [ 95, 90, 96 ] }

如何查询以检索包含大于80的成绩的文档，包括仅包含查询中匹配项的成绩数组？鉴于上面的例子，我想检索以下结果集：

{ "_id" : 1, "semester" : 1, "grades" : [ 87, 90 ] } // 70 is missing
{ "_id" : 2, "semester" : 1, "grades" : [ 90, 88, 92 ] }
{ "_id" : 3, "semester" : 1, "grades" : [ 85, 100, 90 ] }
{ "_id" : 4, "semester" : 2, "grades" : [ 85, 80 ] } // 79 is missing
{ "_id" : 5, "semester" : 2, "grades" : [ 88, 88, 92 ] }
{ "_id" : 6, "semester" : 2, "grades" : [ 95, 90, 96 ] }

Answer 1

您可以使用aggregation framework：

执行此操作

db.collection.aggregate([
    {
        // Emit a new document for each grade in the "grades" field
        "$unwind" : "$grades"
    },
    {
        // Only emit documents whose "grades" field is at least 80
        "$match" : {
            "grades" : {
                "$gte" : 80
            }
        }
    },
    {
        // Group documents back together by original _id
        "$group" : {
            "_id" : "$_id",
            "semester": {$first: "$semester"},
            "grades" : {
                "$push" : "$grades"
            }
        }
    }
]);

MongoDB - 所有数组元素的投影与查询匹配

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