How to join multiple tables in MongoDB like SQL JOIN

Question

mailbox

mailbox:{ _id:"2", title:"test" }

mailbox_details

mailbox_details:{ _id:"1", mailbox_id:2, is_read : false }

These are the tables.

I have attached the image of code please check.

-Unfortunately I did not get the result I expected

Below is the output I intended

output

{ title:"test", mailbox_id:2, is_read : false }.

Once I get this, I can take the next step. please help me.

You need to check your $match object. you are matching true. This will not fulfill your result. You can use $project to filter the response — harpreet cheema
– harpreet cheema, Commented Jul 20, 2020 at 14:18
Thanks @harpreetcheema .I have already tried this. But I did not get the result I expected. db.collection("mailbox_details").aggregate([ { $lookup: { localField: "mailbox_id", from: "mailboxes", foreignField: "_id", as: "mailinfo" } }, { $match : { "mailinfo.is_read" : true } }, { $unwind: "$mailinfo" }, { $project: { "is_read": 1, "mailbox_id": 1, "mailinfo.title": 1, } } ]).toArray((err: any, result: any) => { if (err) { throw err; } console.log("result", result); }); — Arun Das
– Arun Das, Commented Jul 21, 2020 at 3:53

harpreet cheema · Accepted Answer · 2020-07-26 19:56:19Z

1

Try with this. I am using mailbox_details as a parent collection.

db.collection("mailboxes").aggregate([
  { $match : {
      "is_read": true
    }
  },
  { $lookup: { localField: "_id", from: "mailbox_details", foreignField: "mailbox_id", as: "mailinfo"
    }
  },
  { $unwind: "$mailinfo"
  },
  { $project: {
      "is_read": 1,
      "mailbox_id": 1,
      "mailinfo.title": 1,
    }
  }
]).toArray((err: any, result: any) => { if (err) { throw err;
  } console.log("result", result);
});

answered Jul 26, 2020 at 19:56

harpreet cheema

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3 Comments

Arun Das Over a year ago

Thanks @HermenpreetSingh. Let me try and see if it works

Arun Das Over a year ago

Hi @HermenpreetSingh . This is the output of this code. result []. Not Working

Hermenpreet Singh Over a year ago

@ArunDas Please share your collection data , I will try on my local.

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How to join multiple tables in MongoDB like SQL JOIN

mailbox

mailbox_details

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