Updating Single Item in an Array Field in Firestore
The FirebaseFirestore documentation describes ways to interact with array fields, including adding or removing elements. However, it lacks a method for directly updating an item inside the array.
For a document like:
{
name: 'Foo',
items: [
{
name: 'Bar',
meta: {
image: 'xyz.png',
description: 'hello world'
}
},
{
name: 'Rawr',
meta: {
image: 'abc.png',
description: 'hello tom'
}
}
]
}To modify a nested property like items[0].meta.description, the following approach won't work:
const key = `items.${this.state.index}.meta.description`;
const property = `hello bar`;
this.design.update({
[key]: property
}).then(() => { console.log("done")
}).catch(function(error) {
message.error(error.message);
});It removes all properties in the targeted array index and only keeps the description property.
Rewriting the entire object also isn't desirable:
const key = `items.${this.state.index}.meta`;
const property = e.target.value;
let meta = this.state.meta;
meta[e.target.id] = property;
this.design.update({
[key]: meta
}).then(() => {
this.setState({
[key]: meta
})
}).catch(function(error) {
message.error(error.message);
});It converts the entire items array into an object.
Instead, read the array from the document, make changes in memory, and update the entire modified array field:
const docRef = firestore.collection('collection').doc('document');
docRef.get().then(doc => {
const items = doc.data().items;
items[0].meta.description = "hello bar";
docRef.update({
items: items
});
});This ensures only the intended property is updated in the array element.
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