MongoDB : How to compare object values to array values and add a field in this object

Question

I have a MongoDB with this structure:

Registration is an array & it's Object look like this:

{
        "_id" : ObjectId("5e844235ead49b7ff33962d3"), 
        "date" : "2-jul", 
        "firstname" : "John", 
        "lastname" : "Doe", 
        "email" : "[email protected]", 
        "education" : "University", 
        "gender" : "male", 
        "age" : "32", 
        "workshop" : [2,3,6]
}

And known looks like this:

"known" : [
        "[email protected]", 
        "[email protected]", 
        "[email protected]"
]

How can you check if registrations.email exists in known? If it exist how can you add a field to registrations: emailIsKnown: true or emailIsKnown: false?

I've tried different variations of filter, replaceRoot, lookUp with pipelines and mergeObject. But I can't seem to figure out how to only accomplish a minimum of comparing results or adding a field to the registrations object.

Is registrations an array of objects or an object ?

whoami - fakeFaceTrueSoul
– whoami - fakeFaceTrueSoul

2020-04-01 17:22:00 +00:00
Commented Apr 1, 2020 at 17:22 — whoami - fakeFaceTrueSoul
– whoami - fakeFaceTrueSoul, Commented Apr 1, 2020 at 17:22
@whoami an array of objects

Vialito
– Vialito

2020-04-01 17:45:39 +00:00
Commented Apr 1, 2020 at 17:45 — Vialito
– Vialito, Commented Apr 1, 2020 at 17:45

whoami - fakeFaceTrueSoul · Accepted Answer · 2020-04-01 19:48:37Z

1

You can do that using aggregation-pipeline, try below query :

db.collection.aggregate([
  /** Re-create 'registration' array field */
  {
    $addFields: {
      registration: {
        $map: {
          input: "$registration", // Iterate on 'registration' array
          in: {
            $cond: [
              { $in: ["$$this.email", "$known"] }, // Check if current object's email exists in 'known' array
              { $mergeObjects: [{ emailIsKnown: true }, "$$this"] }, // If Yes, add new field with true to existing Object
              { $mergeObjects: [{ emailIsKnown: false }, "$$this"] } // If No, add new field with false to existing Object
            ]
          }
        }
      }
    }
  }
]);

Test : MongoDB-Playground

answered Apr 1, 2020 at 19:48

whoami - fakeFaceTrueSoul

18.1k6 gold badges35 silver badges51 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Vialito Over a year ago

Thanks whoami, it's really nice to have an extended example like yours including the this keyword, map and a condition. I'm gonna have a lot of fun with this from now on forwards. Your solution worked instantly, thank you!

Collectives™ on Stack Overflow

MongoDB : How to compare object values to array values and add a field in this object

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related