CODEWITHSUNDEEP
node.jsmongodbaggregation-framework
Amit Wagner
Amit Wagner

Reputation: 3264

mongodb - How to access lookup results in another lookup in aggregation?

I'm trying to search in lookup based on the previous lookup but no luck.

I get all the results I'm supposed to get but office is returning always an empty array what am i missing here?

query[2] = {
            $lookup: {
                from: "users",
                let: {sales_agent: "$sales_agent"},
                pipeline: [
                    {$match: {$expr: {$eq: ['$_id', '$$sales_agent']}}},
                    {$project: {_id: 1, username: 1, office: 1}},
                ],
                as: "sales_agent"
            }
        };
        query[3] = {
            $lookup: {
                from: "offices",
                let: {office: "$sales_agent.0.office"}, //this value supposed to be come from the previous lookup
                pipeline: [
                    {$match: {$expr: {$eq: ['$_id', '$$office']}}},
                    {$project: {_id: 1, city: 1,}},
                ],
                as: "office"
            }
        };

Upvotes: 2

Views: 1153

Answers (1)

s7vr
s7vr

Reputation: 75934

Use $arrayElemAt to access the element from previous lookup array.

Try

let: {elem: {$arrayElemAt:["$sales_agent", 0]}}

&

{$match: {$expr: {$eq: ['$_id', '$$elem.office']}}}

or in one modification

let: {office: {$let:{vars:{elem:{$arrayElemAt:["$sales_agent", 0]}}, in:"$$elem.office"}}}

Upvotes: 1

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