Mongodb左连接-aggregate聚合函数查询

文章目录

目标数据

源数据

表名：Address

相对于传统数据库写法

    select ad._id as adId,ad.name,o.h,o.w 
    from adress as ad
    left join order as  o on o._id=ad.aId;

mongodb-aggregate左连接写法

db.address.aggregate([
    {$unwind:{
        path:"$order",
        preserveNullAndEmptyArrays:true}
    },
    {$project:{
        _id:1,
        name:1,
        h:"$order.h",
        w:"$order.w",
        uom:"$order.uom"
        }
    }
]);