如何在Firestore中检索子集合的文档? [英] How to retrieve documents of a sub collection in Firestore?

问题描述

我有一个数据库，其结构如下图所示:

I have a db with structure like in the image below:

在这里，我需要拥有多个品牌，并且每个品牌下还需要多个子品牌.我以前尝试过使用地图"，但是确实很乱，并且还了解到拥有多个文档会更好.我对此很陌生，并且已经为此奋斗了3-4天.任何帮助将不胜感激.

Here, I need to have multiple brands, and also multiple sub brands under each brand. I tried with 'maps' before, but it was really messy and also learned that it's better to have multiple documents. I am very new to this and has been struggling with it for 3-4 days now. Any help would be much appreciated.

  firebaseFirestore.collection("Coffee").addSnapshotListener(new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
            if (e != null) {
                Log.d(TAB, "Error : " + e.getMessage());
            }
            for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {
                if (doc.getType() == DocumentChange.Type.ADDED) {
                    Log.d("Brand Name: ",doc.getDocument().getId());

                  //  how to retrieve documents of subCollection here? something like doc.getDocument().collection??

                }

            }

        }
    });

谢谢.

推荐答案

这真的很简单，尝试一下.

This is really simple and easy try this.

 firebaseFirestore.collection("Coffee").addSnapshotListener(new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
            if (e != null) {
                Log.d("", "Error : " + e.getMessage());
            }
            for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {
                if (doc.getType() == DocumentChange.Type.ADDED) {
                    Log.d("Brand Name: ", doc.getDocument().getId());
                    doc.getDocument().getReference().collection("SubBrands").addSnapshotListener(new EventListener<QuerySnapshot>() {
                        @Override
                        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
                            if (e != null) {
                                Log.d("", "Error : " + e.getMessage());
                            }

                            for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {
                                if (doc.getType() == DocumentChange.Type.ADDED) {
                                    Log.d("SubBrands Name: ", doc.getDocument().getId());
                                }
                            }

                        }
                    });
                }

            }
        }});

注意:我已经更新了答案.显然，您无法通过单个请求来获取集合文档中的子集合.

Note: i have updated the answer. It is obvious that you can't fetch sub collections within the collection's document with a single request.

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