在 Android (Java) 中，从包含当前用户的 email 地址的文档中获取所有评论

Question

In my collection of eateries, each eatery has a unique random ID. Within each eatery document there may be a field named 'reviews'. Each review is a map and is stored under a user's email address. Is there any way I can query the database as a whole and get all the reviews for one user email address? I've tried several things, such as storing the user email as a field within the map and using dot notation to try and pull out the review, but to no avail. The best I've come up with so far:

db.collection("eateries")
    .whereEqualTo("reviews" , userEmail)
    .get()
    .addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
        @Override
        public void onComplete(@NonNull Task<QuerySnapshot> task) {

            Log.d(TAG, "restoreReviews onComplete: task.getResult(): " + task.getResult().size());

            if (task.isSuccessful()) {

                Log.d(TAG, "restoreReviews onComplete: task was successful");

                for (QueryDocumentSnapshot document : task.getResult()) {
                }

            } else {
                Log.d(TAG, "restoreReviews Error getting documents: ", task.getException());
            }
        }
    });

Just to reiterate, reviews contains maps of review objects (which are in turn also maps):

A user could leave reviews for lots of eateries (in other documents) and I'd like to retrieve them all. eateriesTest is just a dummy collection to show the types of documents I'm querying, without displaying users' actual email addresses. Any pointers would be greatly appreciated.

Answer 1

Because you're trying to query an array of reviews the whereEqualTo method doesnt do what youre looking for here. If you replace it with whereArrayContains() method that should fix your problem.

Answer 2

The structure of your database does not allow for the kind of query you're trying to do. Firestore can't query for the existence of keys within a map field. It can only query on the values of map keys.

You will have to add the email addresses to the document in a way that can actually be queried. For example, they could be stored as individual elements of an array type field, and filtered with an array-contains query. It's common to duplicate information like this in order to satisfy your queries.

For example, if you have an array field "reviewers" with only the strings of each email, you could filter them like this:

.whereArrayContains("reviewers" , userEmail)