Question

下面的代码首先在一个字段上加入两个集合，并尝试过滤其他字段上的值。

db.zeroDimFacts.aggregate(
{$lookup:{from:"zeroDim",localField:"Kind",foreignField:"Model", as:"EmbedUp"}},
{$project: {"EmSub":"$EmbedUp.Sub","Result": {$eq:["$Type","$EmbedUp.Sub"]}, "type":"$Type"}})

请检查下面的代码输出。即使＆＃39; EmSub＆＃39; ＆安培; ＆＃39; $类型＆＃39;具有相同的价值，它没有显示在＆＃39;结果＆＃39;领域。如果是因为＆＃39; EmSub＆＃39;显示为数组，如何仅比较该数组中包含的值？

/* 1 */
{
    "_id" : NumberLong(1),
    "EmSub" : [ 
        "Fruit"
    ],
    "Result" : false,
    "type" : "Fruit"
}

/* 2 */
{
    "_id" : NumberLong(2),
    "EmSub" : [ 
        "Fruit"
    ],
    "Result" : false,
    "type" : "Fruit"
}

/* 3 */
{
    "_id" : NumberLong(3),
    "EmSub" : [ 
        "Fruit"
    ],
    "Result" : false,
    "type" : "Fruit"
}

Answer 1

您可以展开数组以与其元素进行比较：

db.zeroDimFacts.aggregate([{$lookup:{from:"zeroDim",localField:"Kind",foreignField:"Model", as:"EmbedUp"}},
{$unwind: "$EmbedUp"},
{$project: {"EmSub":"$EmbedUp.Sub","Result": {$eq:["$Type","$EmbedUp.Sub"]}, "type":"$Type"}}]);

它可以为单个zeroDimFacts _id提供多个结果，但是您可以再次对它们进行分组

db.zeroDimFacts.aggregate([{$lookup:{from:"zeroDim",localField:"Kind",foreignField:"Model", as:"EmbedUp"}},
{$unwind: "$EmbedUp"},
{$project: {"EmSub":"$EmbedUp.Sub","Result": {$eq:["$Type","$EmbedUp.Sub"]}, "type":"$Type"}},
{$group: {_id: "$_id", EmSub: {$push: "$EmSub"}, Result: {$push: "$Result"}, type: {$push: "$type"}}}]);

mongodb：无法从$ project和$ eq获取结果

1 个答案: