Question

我有一个非常简单的使用$ lookup和$ match的MongoDb查询。我的问题是我无法确定查询中$ match的正确位置。如果我将$ match放在$ lookup之上，我会得到预期的（通过$ match正确过滤）结果，但它们不包含链接文档的“world”数组。如果我将$ match放在查询下方，我会获得所有父记录，包括链接文档的“world”数组，但$ match不起作用。

我做错了什么？...

server.get(`${routePfx}/${model}s/with-linked`, function (req, res, next) {
    console && console.log('Finding all with linked names ' + model.toUpperCase() + 's...');
    db.collection(model).aggregate(
        {
            "$lookup": {
                from: "world",
                localField: "worldId",
                foreignField: "_id",
                as: "world"
            }
        },
        { "$match": { "del": false } }
    ).toArray(function (err, docs) {
        res.json(201, docs);
        next();
    });
});

编辑：我发现了它！你注意到了这个微小的差异吗？...

server.get(`${routePfx}/${model}/:id/with-linked`, function (req, res, next) {
    console && console.log('Finding ' + model.toUpperCase() + ' by Id with linked names...');
    db.collection(model).aggregate([
        { "$match": { "_id": new ObjectId(req.params.id) } },
        {
            "$lookup": {
                from: "world",
                localField: "worldId",
                foreignField: "_id",
                as: "world"
            }
        }
    ]).toArray(function (err, docs) {
        res.json(201, docs);
        next();
    });
});

Answer 1

聚合函数需要一个数组......

server.get(`${routePfx}/${model}/:id/with-linked`, function (req, res, next) {
    console && console.log('Finding ' + model.toUpperCase() + ' by Id with linked names...');
    db.collection(model).aggregate([
        { "$match": { "_id": new ObjectId(req.params.id) } },
        {
            "$lookup": {
                from: "world",
                localField: "worldId",
                foreignField: "_id",
                as: "world"
            }
        }
    ]).toArray(function (err, docs) {
        res.json(201, docs);
        next();
    });
});

MongoDb RestAPI查询$ match上/下$ lookup更改结果

1 个答案: