$ lookup从其他集合中返回不匹配的项

Question

我一直认为preserveNullAndEmptyArrays会在不存在的记录上允许$lookup并仍然返回主结果。

不幸的是在这种情况下我只从AAA获取数据 - 我想要来自AAA和BBB的数据。

属性表

{
    _id: "AAA",
    name: "Property AAA"
},
{
    _id: "BBB",
    name: "Property BBB"
}

hotdeal表

{
    _id: "001",
    property: "AAA",
    active: true,
    text: "very good deal"
}

汇总

db.property.aggregate([
{ $match: {} },
{
    $lookup: {
        from: "hotdeal",
        localField: "_id",
        foreignField: "property",
        as: "hotdeals"
    }
},
{ 
    $unwind: { 
        path: "$hotdeals", preserveNullAndEmptyArrays: true
    }
}, 
{                                                   
    $match: {                                       
        "hotdeals.active": true
    }
},
{
    $project: {
        _id : 0,
        name : 1,
        "text" : "$hotdeals.text"
    }
}
])