查找聚合中的管道在 mongodb 中不起作用 [英] Pipeline in lookup aggregation not working in mongodb

问题描述

我是 mongodb 的新手，所以我希望这不会成为一个非常基本的问题.我做了一些研究并尝试应用我发现的东西，但似乎有些东西让我无法理解.

I am new to mongodb so I hope this does not come-off as a very elementary question. I've done some research and tried to apply what I've found but something just seems to escape me.

我有两个以下格式的集合:

I have two collections of the following format:

-----------------------------------------------------------------------
Shop
-----------------------------------------------------------------------
{
    "shopId": "1002",
    "shopPosId": "10002",
    "description": "some description"
}

-----------------------------------------------------------------------
Compte
-----------------------------------------------------------------------
{
    "shopId": "9000",
    "shopPosId": "0000",
    "clientUid": "474192"
}

我想加入这些，在这样做之前，我想过滤掉没有 shopPosId 字段的 Shops.

I want to join those and before doing so, I want to filter out the Shops which do not have the shopPosId field.

这是我的代码:

Compte.aggregate([
    {
        $match:
            { 
                $and:[{"clientUid":clientUid}]
            }
    },
    {      
        $lookup:
        {
            from: "Shop",
            localField: "shopId",
            foreignField: "shopId",
            let: {"Shop.shopPosId": "$shopPosId"},
            pipeline: [{$match: {"shopPosId": {"$exists": false}}}],
            as: "shopDescr"
        }
        }]
);

返回的结果是一个undefined，这意味着查询没有多大意义(因为实际上我至少应该得到一个空数组).

the returned result is an undefined, which means the query doesn't make much sense (because in fact I should at least get a void array).

这是因为两个集合都有 shopPosId 字段吗?(如果是这样，这行不是 let: {"Shop.shopPosId": "$shopPosId"} 应该处理它吗?)

Is this because the two collections have the shopPosId field? (if so, isn't this line let: {"Shop.shopPosId": "$shopPosId"} supposed to take care of it ?)

推荐答案

正如 Alex 所说，您正在混合 $lookup 语法在这里...所以正确的是

As Alex commented you are mixing both the $lookup syntax here... So the correct will be

Compte.aggregate([
  { "$match": { "$and": [{ "clientUid": clientUid }] }},
  { "$lookup": {
    "from": "Shop",
    "let": { "shopId": "$shopId" },
    "pipeline": [
      { "$match": {
        "$expr": { "$eq": [ "$shopId", "$$shopId" ] },
        "shopPosId": { "$exists": false }
      }}
    ],
    "as": "shopDescr"
  }}
])

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