Cloud firestore: Update field values in nested array object with dot notation

Question

Please help me solve this, I would like to update the fields using dot notation, using set() but each time I run with the below implementation. I have the fields added to firestore as e.g studentInfo.0.course.0.courseId instead of updating the already existing ones.

Json sample as it sits in firestore

    "schoolId": "school123",
    "studentInfo": [
        {
            "studentId": "studentI23",
            "regDate": "2020-04-18",
            "course": [
                {
                    "courseId": "cs123",
                    "regDate": "2020-05-28",
                    "status": "COMPLETED"
                }
            ]
        
        }
    ],
    "registered":"yes"
}

Code logic

const query = firestore.collection('users').where('registered', '==', 'yes')
const students = await query.get()
 students.forEach(student => {
    firestore.doc(student.ref.path).set({
        'studentInfo.0.studentId': '345','studentInfo.0.course.0.courseId': '555'
      }, { merge: true })
 })

On the docs https://firebase.google.com/docs/firestore/manage-data/add-data#update_fields_in_nested_objects I can only find updating nested objects but not nested array objects.

Frank van Puffelen Frank van Puffelen · Accepted Answer · 2020-10-19T14:34:58

It is indeed not possible to update a single element in an array using dot notation, or otherwise. To update an array you'll need to:

Read the document
Get the current value of the array from it
Determine the new array contents
Write the entire updated array back to the database.

The only alternative array operations are array-union and array-remove, which add and remove unique elements to/from the array - essentially treating it as a mathematical set. But since you are looking to update an existing element, these operations are of no use here.

Also see:

Cloud firestore: Update field values in nested array object with dot notation

1 Answers