How to push an object in an array with arrayUnion() in Firebase Firestore?

Question

My current document looks like this:

{
    "assignmentName": "OS Assignment-2",
    "dueDate": "10 August",
    "createdAt": "2020-08-02T20:27:28.916Z",
    "maxMarks": 10,
    "facutyName": "Dr. Muskan Gupta",
    "semester": "3",
    "submittedBy": [
        {
            "studentName": "Test name",
            "downloadUrl": "URL"
        },
        {
            "downloadUrl": "URL3",
            "studentName": "Test name2"
        },
        {
            "downloadUrl": "https://downloadthisfile.com",
            "studentName": "Nakshatra Saxena"
        },
        {
            "studentName": "Hello Bortehr",
            "downloadUrl": "httpsav"
        }
    ],
    "program": "CSE",
    "subject": "Operating System with UNIX"
}

I want to push an object in the 'submittedBy' field but I get an error. The code I'm using right now is:

const submittedAssignment = {
    studentName: req.body.studentName,
    downloadUrl: req.body.downloadUrl,
    };
    admin
        .firestore()
        .collection("assignments")
        .doc(req.params.assignmentId)
        .update({
          submittedBy: firebase.firestore.FieldValue.arrayUnion(submittedAssignment)
        });
    })
    .then(() => {
      return res
        .status(201)
        .json({ message: `Assignment submitted successfully` });
    })
    .catch((err) => {
      console.error(err);
      res.status(500).json({ error: `Error submitting assignment` });
    });

But I'm getting this error

Error: Update() requires either a single JavaScript object or an alternating list of field/value pairs that can be followed by an optional precondition. Value for argument "dataOrField" is not a valid Firestore document. Couldn't serialize object of type "FieldValueDelegate" (found in field "submittedBy"). Firestore doesn't support JavaScript objects with custom prototypes (i.e. objects that were created via the "new" operator).

Don't use images for text and code. I rolled back to the edit I made to fix the code using triple backtick code fences - I suggest learning how to use them. — Doug Stevenson
– Doug Stevenson, Commented Aug 2, 2020 at 21:33
Hey thanks for the edit. I'm new here, I'll learn to use that now. Thanks a lot. — Nakshatra Saxena
– Nakshatra Saxena, Commented Aug 3, 2020 at 12:12

Doug Stevenson · Accepted Answer · 2020-08-02 21:39:37Z

8

You're mixing up Firestore SDKs. If you use the Admin SDK to make the update, you will also need to use the Admin SDK to specify FieldValue type values.

Instead of this:

      submittedBy: firebase.firestore.FieldValue.arrayUnion(submittedAssignment)

Use this:

      submittedBy: admin.firestore.FieldValue.arrayUnion(submittedAssignment)

answered Aug 2, 2020 at 21:39

Doug Stevenson

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2 Comments

Nakshatra Saxena Over a year ago

It works perfectly now. Thank you so much, I thought about this too earlier and changed it to admin.firestore(), another silly mistake. Thanks again!

Doug Stevenson Over a year ago

Good to know. On Stack Overflow, it's customary to accept helpful answers as correct using the checkmark button on the left.

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