How Can I Update a Nested Field in an Array in Firestore?

Firestore: Updating Nested Array Fields

Problem Statement:

You have a document in Firestore with an array field containing objects. You need to update a specific field within an object inside the array. However, attempting to update directly using the dot notation (items.${index}.meta.description) doesn't work correctly.

Solution:

Firestore does not currently support directly updating a specific element in an indexed array. Instead, consider the following alternatives:

Option 1: Rewrite the Entire Array

Instead of updating the specific field, read the entire array from the document, make the desired modification in memory, then update the modified array field as a whole:

const key = `items.${this.state.index}.meta`;
let items = this.state.items;
items[this.state.index].meta.description = 'hello bar';

this.design.update({
  [key]: items,
})

This approach effectively rewrites the entire array, which may be inefficient if the array is large.

Option 2: Use Array Operations

While Firestore doesn't allow direct updates to existing array elements, you can still add or remove elements using array operations. For example, to append a new element to the array:

this.design.update({
  items: FieldValue.arrayUnion({
    name: 'New Item',
    meta: {
      image: 'def.png',
      description: 'hello new item',
    }
  })
})

To remove an element, use FieldValue.arrayRemove().

Recommendation:

If the array is relatively small, Option 1 (rewriting the entire array) can be a straightforward solution. However, if the array is large, Option 2 (using array operations) is more efficient as it avoids overwriting the entire array.

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