mongoDB在多个字段上联接 [英] mongoDB Join on multiple fields

问题描述

我正在将SQL查询重写为mongoDB.有人可以帮助我们如何使用多个联接键和条件联接两个集合，例如下面的SQL查询.

I am rewriting SQL Queries into mongoDB. Can someone help how do we join two collections with multiple join keys and conditions like in below SQL Query.

SELECT S.* FROM LeftTable S
LEFT JOIN RightTable R ON S.ID =R.ID AND S.MID =R.MID WHERE R.TIM >0 AND S.MOB IS NOT NULL

我有以下与单连接键条件有关的代码.如果有人可以帮助使用多个连接键和where子句来完成查询，我将感到很高兴.

I have the below code which does with single join key condition. I would be glad if someone can help with multiple join keys and where clause to complete query.

db.dim.aggregate([{$lookup:{from:"dimFactsVer11",localField:"Sub", foreignField:"Type", as:"EmbedUp"}}])

推荐答案

当前mongodb $ lookup 仅比较单个 local 和外国键.

Currently mongodb $lookup only compare single local and foreign key.

但是，如果您要执行像mysql左连接两个或多个字段那样的查询，则下面是解决方法.

But if you want to perform a query as like mysql left join with two or more filed then below is solution.

db.getCollection('LeftTable').aggregate([
{
    $lookup:
        {
          from: "RightTable",
          localField: "ID",
          foreignField: "ID",
          as: "RightTableData"
        }
},  
{$unwind :"$RightTableData" },
{ 
     $project: { 
            mid: { $cond: [ { $eq: [ '$MID', '$RightTableData.MID' ] }, 1, 0 ] } 
        } 
},
{$match : { mid : 1}}

])

此处$ MID是 LeftTable MID字段.

Here $MID is LeftTable MID field.

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