How Can I Update a Single Item in an Array Field in Firestore?

Updating a Single Item in an Array Field in Firestore

You have an array field called items in a Firestore document, and you want to update a field within one of the objects in the array.

Initial Attempt

Your initial attempt used the following code:

const key = `items.${this.state.index}.meta.description`
const property = `hello bar`;

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

However, this removed the entire object at the specified array index, leaving only the description field.

Modified Attempt

Your modified attempt used the following code:

const key = `items.${this.state.index}.meta`
const property = e.target.value;
let meta = this.state.meta;
meta[e.target.id] = property;

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

This seemingly converted the items array into an object, losing the array structure.

Firestore's Limitations

Firestore has limitations in updating array fields. It only allows adding or removing elements, not modifying existing ones.

Solution

To modify an item in an array field, you need to read the entire array, make the necessary changes in memory, and then update the entire modified array field.

const items = this.design.get("items"); // Read the array field
items[this.state.index].meta.description = "hello bar"; // Modify the item
this.design.update({
  items: items // Update the entire modified array
})
...

By using this approach, you can update the specific item within the array field without losing the array structure.

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