MongoDB – aggregate match field from the previously matched document

June 8, 2023

I have a collection with following schema –

const ContentSchema = new Schema({
    label: {
        type: String
    },
    itemId: {
        type: Schema.ObjectId,
        refPath: 'onModel'
    },
    formId: {
        type: Schema.ObjectId,
        refPath: 'onModel'
    },
    value: {
        type: Schema.Types.Mixed,
        index: "text"
    },
}, { timestamps: true, versionKey: false });

Here are some example documents the collection may have –

{
  _id: ObjectId('647b1538c29a553ad6e8f316'),
  label: "Name",
  itemId: ObjectId('647b1538c29a553ad6e8f313'),
  formId: ObjectId('647b1538c29a553ad6e8f913'),
  value: "ABC"
},
{
  _id: ObjectId('647b1538c29a553ad6e8f416'),
  label: "Email",
  itemId: ObjectId('647b1538c29a553ad6e8f313'),
  formId: ObjectId('647b1538c29a553ad6e8f913'),
  value: "def@mail.com"
},
{
  _id: ObjectId('647b1538c29a553ad6e8f516'),
  label: "Name",
  itemId: ObjectId('647b1538c29a553ad6e8f320'),
  formId: ObjectId('647b1538c29a553ad6e8f913'),
  value: "MNO"
},
{
  _id: ObjectId('647b1538c29a553ad6e8f616'),
  label: "Email",
  itemId: ObjectId('647b1538c29a553ad6e8f320'),
  formId: ObjectId('647b1538c29a553ad6e8f913'),
  value: "xyz@mail.com"
}

Now, I need to perform a query to search "ABC" from the collection with formId – ObjectId('647b1538c29a553ad6e8f913').

Here is the code to do that –

return await ContentModel.aggregate([
{
    $match: {
        $text: { $search: text },
        formId: new mongoose.Types.ObjectId(formId)
    }
}]

The above code is absolutely working fine and returns the document –

{
    _id: ObjectId('647b1538c29a553ad6e8f316'),
    label: "Name",
    itemId: ObjectId('647b1538c29a553ad6e8f313'),
    formId: ObjectId('647b1538c29a553ad6e8f913'),
    value: "ABC"
}

But I need more records within the same aggregation. Now I need to find out other documents from the document with itemId – ObjectId('647b1538c29a553ad6e8f313').

So that the aggregation should now return 2 documents –

    {
      _id: ObjectId('647b1538c29a553ad6e8f316'),
      label: "Name",
      itemId: ObjectId('647b1538c29a553ad6e8f313'),
      formId: ObjectId('647b1538c29a553ad6e8f913'),
      value: "ABC"
    },
    {
      _id: ObjectId('647b1538c29a553ad6e8f416'),
      label: "Email",
      itemId: ObjectId('647b1538c29a553ad6e8f313'),
      formId: ObjectId('647b1538c29a553ad6e8f913'),
      value: "def@mail.com"
    }

I am trying with following query which does not work –

return await ContentModel.aggregate([
{
    $match: {
        $text: { $search: text },
        formId: new mongoose.Types.ObjectId(formId)
    }
},
{
    $match: { itemId: "$itemId" }
}]

>Solution :

If I’ve understood correctly you can use $lookup with your own collection in this way:

In this query you can $match as you have done and then, with matching results you can $lookup (like a SQL JOIN) against your data using collection and matching itemId.

So is like to say "join the matching itemId with all others itemId". And I think is what you want.

db.collection.aggregate([
  {
    "$match": { /* your match*/ }
  },
  {
    "$lookup": {
      "from": "collection",
      "localField": "itemId",
      "foreignField": "itemId",
      "as": "results"
    }
  },
  {
    "$unwind": "$results"
  },
  {
    "$replaceRoot": {
      "newRoot": "$results"
    }
  }
])

Also the two others steps are to output the result as root.

Example here