CODEWITHSUNDEEP
mongodbcollectionsmergeforeign-keysaggregate
babeyh
babeyh

Reputation: 699

Merge two collection with specific fields in mongodb

I have 2 collection, issues and repos.

issues : issue_id, body, full_name, ...

repos : repo_id, title, full_name, ...

I want to add "repo_id" field to issues collection. (with foreign field full_name)

After this process desired output collection;

issues2: issue_id, body, full_name, repo_id ...

db.getCollection("issues").aggregate([
   {
      $lookup: {
         from: "repos",
         localField: "full_name",    // field in the orders collection
         foreignField: "full_name",  // field in the items collection
         as: "fromissues"
      }
   },
   {
      $replaceRoot: { newRoot: { $mergeObjects: [ { $arrayElemAt: [ "$fromissues", 0 ] }, "$$ROOT" ] } }
   },
   { $project: { fromissues: 0 } },
   {$out: "issues2"}

])

I can use this query to merge 2 collection with whole fields. How can select only repo_id field? I tried to change this row but it didnt work.

{ $project: { "id":1, "full_name":1} },

If I use project, I must add to project "all columns of issues collection" + repo_id + full_name 

{ $project: { "id":1, "body":1, ...(24 fields)... "repo_id":1 "full_name":1} },

Upvotes: 1

Views: 334

Answers (1)

Mahesh Bhatnagar
Mahesh Bhatnagar

Reputation: 1080

Not use {$out: "issues2"} keyword in query

     db.store.aggregate([
   {
      $lookup: {
         from: "testers",
          let: { item: "$fullName" },
           pipeline: [
              { $match:
                 { $expr:
                    { $and:
                       [
                         { $eq: [ "$fullName",  "$$item" ] },
                       ]
                    }
                 }
              },
              { $project: { repo_id: 1 } }
           ],
         as: "fromissues"
      }
   },
   {
      $replaceRoot: { newRoot: { $mergeObjects: [ { $arrayElemAt: [ "$fromissues", 0 ] }, "$$ROOT" ] } }
   },
   { $project: { 'fromissues': 0 } },

])

Upvotes: 1

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