How to Update a Single Item in a Nested Array Field in Firestore?

How to Update a Single Item in an Array Field within Firestore

In Firestore, arrays can be nested within documents. However, it's important to understand that array fields in Firestore behave differently from arrays in other programming languages.

Problem Statement:
Updating a specific element within an array field in a Firestore document can be challenging. Attempts to directly update a nested field within an array, such as items[0].meta.description, can lead to unexpected outcomes.

Initial Approach:
Initially, you tried to update a nested field by using the following code:

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

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

However, this approach removed all other fields from the object at the specified index.

Alternative Approach:
In your subsequent attempt, you rewrote the entire meta object:

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
})

While this approach successfully updated the nested field, it converted the array into an object.

Solution:
Firestore does not provide a direct way to update a specific item within an array. Instead, you must read the entire array out of the document, modify it in memory, and then update the entire array field.

This can be achieved using the following steps:

1. Read the entire array from the document using the get() method.
2. Use methods like map() or find() to locate and modify the specific element within the array.
3. Update the array field using the set() or update() method with the modified array.

Here's an example code:

const docRef = firestore.doc(`document/${id}`);

let items;
// Read the document and retrieve the items array
await docRef.get().then((doc) => {
  if (doc.exists) {
    items = doc.data().items;
  }
});

// Update the specific element in the array
const updatedItem = items.find((item) => item.name === 'Bar');
updatedItem.meta.description = 'hello bar';

// Update the entire array field with the modified array
await docRef.update({ items });

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