In Firestore, how can you do a compound query involving a key in a map without creating an index for every key?

Question

In Firestore, how can you do a compound query involving a key in a map without creating an index for every key?

For example, consider a collection which holds blog posts

Answer 1

Now Firestore allows the array-contains operator.
If you want to filter documents which contain specific value, try this.

First, change Map field to Array field.

Post {
    title: ..
    ...
    categories: [
        cats,
        puppies
    ]
}

Second, use array-contains and orderBy for each different fields.

let query = db.collection(`/posts`)
    .where('categories', 'array-contains', 'cats')
    .orderBy('createdAt')
    .startAfter(lastDate)
    .limit(5);

You can check the official document about array-contains operator from here.