Firestore’s array-contains or array-contains-any operators are useful in scenarios where you need to filter documents based on the presence of certain elements within an array field. For instance, consider a social media application where each user document has a ‘friends’ array field containing the IDs of their friends. If we want to find all users who are friends with a specific user (say User A), we can use the array-contains operator in our query. The query would look like this: db.collection(‘users’).where(‘friends’, ‘array-contains’, ‘User A ID’). This will return all documents where the ‘friends’ array contains ‘User A ID’. Similarly, if we have multiple user IDs and we want to find any user who is friends with any of these users, we can use the array-contains-any operator.
