Mongo DB aggregation on array

Question

im trying to add element to array in document MongoDB collection with Aggregate (not regular update) match to specific name but i dont find the right syntax

for example:

{"name":"TEST1","department":"T1","skills":["JS","HTML"],"expY":5}
{"name":"TEST2","department":"T2","skills":["Java","CSS"],"expY":3}

i want to add to skills array "CSS" i try with sort, match, group, project, ($add, $push etc) and none of those syntax not working

db.collection.aggregate([ 
   { $match : { name : "TEST1" } },
   HERE I DONT KNOW WHAT IS THE RIGHT SYNTAX TO ADD ELEMENT TO skills array
])

codemonkey · Accepted Answer · 2021-01-24 10:13:36Z

1

If I am understading your question correctly, you want to match all the documents with name "TEST1" and then add "CSS" to the skills array. If that's correct, here is one way to do that:

db.collection.aggregate([
  {
    $match: {
      name: "TEST1"
    }
  },
  {
    $project: {
      name: "$name",
      department: "$department",
      expY: "$expY",
      skills: {
        $concatArrays: [
          "$skills",
          [
            "CSS"
          ]
        ]
      }
    }
  }
])

Playground

Here is how to update your document to add "CSS" to the array:

db.your_collection.update({ name : "TEST1" }, { $push: { skills: 'CSS' } })

edited Jan 24, 2021 at 10:13

answered Jan 24, 2021 at 9:13

codemonkey

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2 Comments

Carnjaxx official Over a year ago

thank you for the answer its show that is work but! when i run this query its not really change the array its show me the original array when i look on compass / db.collection.find()

codemonkey Over a year ago

@Carnjaxxofficial Aggregation is not used for updates. You need the simple update command. I have updated my answer to show you how to do that.

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