Find two objects with the same type in mongoDB

Question

I have an arrays of objects as below in my data:

traits = [{type: 'Language' , val: 'English'} , {type: 'Age' , val: 37} , {type: 'Language' , val: 'Spanish'}]

I need to find out if each of the traits arrays I have in my documents, have at least two 'Language' types. if they do update the val to 'MultiLang'.

What is the best way to get this done?

Answer 1

I'm not sure what is your expected result, but if I understand you correctly, you can use update with pipeline:

db.collection.update({},
[
  {$set: {
      language: {$filter: {
          input: "$traits",
          cond: {$eq: ["$$this.type", "Language"]}
      }},
      traits: {$filter: {
          input: "$traits",
          cond: {$ne: ["$$this.type", "Language"]}
      }}
  }},
  {$set: {
      language: {
        type: "Language",
        val: {$cond: [
            {$gt: [{$size: "$language"}, 1]},
            "MultiLang",
            {$first: "$language.val"}
        ]}
      }
  }},
  {$set: {
      traits: {$concatArrays: [
          "$traits",
          [{$first: "$language"}]
      ]},
      language: "$$REMOVE"
  }}
])

See how it works on the playground example