Question 291118 in Mongodb Question posted in
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Add/update element in already existing array in a MongoDB document

I’ve a customer document with attributes array. I want to insert new attributes and update already existing ones.

Already existing "attributes" within the document:

[{
      key: "email",
      value: "[email protected]"
    }, {
      key: "name",
      value: "Somebody"
}]

I want to** add or update** within "attributes"

    [{
      key: "email",
      value: "[email protected]"
    }, {
      key: "mobile",
      value: "1234567890"
    }]

So, the result should be:

[{
key: "email",
value: "[email protected]"
},{
key: "name",
value: "Somebody"
},{
key: "mobile",
value: "1234567890"
}]

I achieved the result using below written code. But I want to use only MongoDB to get the same result.

const { attributes, uid } = req.body;
const customer: any = await getCustomer({ uid });
const oldAttributes = customer?.attributes.filter((attr: any) => !attributes.find((att: any) => att.key === attr.key));
const updatedAttributes = [...oldAttributes, ...attributes];
const response = await updateCustomer({ uid }, { $set: { attributes: updatedAttributes } } );
Tags:

2

Answers


  1. 0

    You can set upsert: true in options when you call updateCustomer as follows:

    const options = { upsert: true };

const response = await updateCustomer({ uid }, { $set: { attributes: updatedAttributes } }, options );

    You can refer to more at: https://www.mongodb.com/docs/drivers/node/current/fundamentals/crud/write-operations/upsert/

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  2. 0

    Since using upsert would overwrite the old attributes with the new attributes, rather than updating just the attributes array, this would need a full pipeline, ending with a merge back into the collection.

    Assuming a document like this:

    [
  {
    _id: 12345,
    attributes: [
      {
        key: "email",
        value: "[email protected]"
      },
      {
        key: "name",
        value: "Somebody"
      }
    ]
  }
]

    Steps at a high-level:

    1. Convert the array of {key: "<key_name>", value: "<value>"} to an object having {<key_name>: <value>, ...}
      • This assumes each key is unique with the array of attributes.
      • Otherwise, the last occurrence overwrites the first.
    2. Merge it with the values provided by the user: so existing values get updated, new value get added, fields not provided remain.
    3. Convert it back to an array of {key: "<key_name>", value: "<value>"}

    User input would be required for the first $match step for the document _id and then for the $mergeObjects step where you add user provided values.

    Notes:

    • It’s possible to use a $let or nested "$set": { "attributes": ... } but it feels cleaner and clearer as separate pipeline steps.
    • If you know the attributes will always be only name, email, mobile, then you can change the object to array step with an explicit set/project with [{"key": "name", "value": "$attribute.name}, {"key": "email", "value": "$attribute.value"}, ...] in the objecToArray step not require the re-mapping of labels after that.
    • For the final merge, I have put whenNotMatched: "fail" since you probably can’t use this for records which don’t already exist.
    • Added an alternate playground using db.collection.update() instead of aggregate. So the final $merge is not required. But you will need to add {upsert: false, multi: false} for the 3rd param; which finally becomes the same length/complexity as the original anyway.
    db.collection.aggregate([
  {
    "$match": {
      // whichever doc you're updating
      "_id": 12345
    }
  },
  {
    // unwrap the key value pairs to actual "key: value"
    "$set": {
      "attributes": {
        "$arrayToObject": {
          "$map": {
            "input": "$attributes",
            "as": "i",
            "in": {
              k: "$$i.key",
              v: "$$i.value"
            }
          }
        }
      }
    }
  },
  {
    // merge it with new/updated data
    "$set": {
      "attributes": {
        "$mergeObjects": [
          "$attributes",
          {
            // this is where you add new field and set existing ones
            "email": "[email protected]",
            "mobile": "1234567890"
          }
        ]
      }
    }
  },
  {
    // convert it back to an arry of [{"k": <k1>, v: <v1>}, {"k": k2, "v": <v2>}]
    "$set": {
      "attributes": {
        "$objectToArray": "$attributes"
      }
    }
  },
  {
    // convert "k" --> "key" and "v" --> "value"
    "$set": {
      "attributes": {
        "$map": {
          "input": "$attributes",
          "as": "e",
          "in": {
            "key": "$$e.k",
            "value": "$$e.v"
          }
        }
      }
    }
  },
  {
    // write to the collection
    $merge: {
      into: "collection",
      on: "_id",
      whenMatched: "replace",
      whenNotMatched: "fail"
    }
  }
])

    Result:

    [
  {
    "_id": 12345,
    "attributes": [
      {
        "key": "email",
        "value": "[email protected]"
      },
      {
        "key": "name",
        "value": "Somebody"
      },
      {
        "key": "mobile",
        "value": "1234567890"
      }
    ]
  }
]

    Mongo Playground

    Alternate, with collection.update().

    PS. I think $objectToArray really needs some options for customising the label for the key and value.

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