如何将子集合中的所有文档获取到Firebase Firestore中的RecyclerView

如何解决如何将子集合中的所有文档获取到Firebase Firestore中的RecyclerView

在我的Firestore数据库中，我有一个带有多个文档的“类别”集合，而这些文档又具有带有相应文档的“产品”子集合。

我正在尝试获取所有子集合中的所有文档，并填充到Recylerview中，但是我失败了。

这是我的代码；

 private void populateAllProducts() {
        Log.d(TAG,"populateAllProducts called: ");
          database
                .collection(Globals.CATEGORIES)
                .get()
                .addOnCompleteListener(task -> {
                    if (task.isSuccessful()) {
                            for (QueryDocumentSnapshot document : Objects.requireNonNull(task.getResult())) {
                                Category category = document.toObject(Category.class);
                                Log.d(TAG,"Category: " + category.getName());
                                    database
                                        .collection(Globals.CATEGORIES)
                                        .document(category.getUuid())
                                        .collection(Globals.PRODUCTS)
                                        .get()
                                        .addOnCompleteListener(task1 -> {
                                            if (task.isSuccessful()) {
                                                    for (QueryDocumentSnapshot snapshot : Objects.requireNonNull(task1.getResult())) {
                                                        Product product = snapshot.toObject(Product.class);
                                                        Log.d(TAG,"All products: " + product.getName());
                                                    }
                                                }
                                        })
                                        .addOnFailureListener(e -> Log.e(TAG,"Error: ",e));
                            }
                    }
                })
                .addOnFailureListener(e -> {
                    vars.verityApp.crashlytics.log("Error while fetching categories");
                    Log.e(TAG,"Error occured: ",e);
                    vars.verityApp.crashlytics.recordException(e);
                });
    }

但我收到此致命异常；

2020-08-11 16:27:16.358 26161-26161/com.verityfoods E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.verityfoods,PID: 26161
    java.lang.NullPointerException: Provided document path must not be null.
        at com.google.firebase.firestore.util.Preconditions.checkNotNull(Preconditions.java:147)
        at com.google.firebase.firestore.CollectionReference.document(CollectionReference.java:103)
        at com.verityfoods.ui.bottomviews.shop.ShopFragment.lambda$populateCategories$2$ShopFragment(ShopFragment.java:87)
        at com.verityfoods.ui.bottomviews.shop.-$$Lambda$ShopFragment$dIuQdpUfodkE_zdMSo4L2Rr4DL0.onComplete(Unknown Source:2)
        at com.google.android.gms.tasks.zzj.run(Unknown Source:4)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

感谢您的帮助！

解决方法

您遇到以下错误：

java.lang.NullPointerException：提供的文档路径不能为null。

因为您要在参考中传递一个null值。 category.getUuid()最有可能返回null，因此出现该错误。看到您的getUuid()吸气剂，我可以猜得出该属性的名称在数据库中不是uuid，所以这很可能是原因。

我正在尝试获取所有子集合中的所有文档，并填充到Recylerview中

要获取所有products子集合中的所有数据，应使用Firestore collection group query而不是常规的CollectionReference对象。在代码中，此查询应如下所示：

db.collectionGroup("products").get().addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
    @Override
    public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
            //Iterate to get the products out of the queryDocumentSnapshots object
        }
    });

,

您正在检查第一项任务是否在第二项任务内完成。

private void populateAllProducts() {
        Log.d(TAG,"populateAllProducts called: ");
          database
                .collection(Globals.CATEGORIES)
                .get()
                .addOnCompleteListener(task -> {
                    if (task.isSuccessful()) {
                            for (QueryDocumentSnapshot document : Objects.requireNonNull(task.getResult())) {
                                Category category = document.toObject(Category.class);
                                Log.d(TAG,"Category: " + category.getName());
                                    database
                                        .collection(Globals.CATEGORIES)
                                        .document(category.getUuid())
                                        .collection(Globals.PRODUCTS)
                                        .get()
                                        .addOnCompleteListener(task1 -> {
                                            if (task.isSuccessful()) { //Here should be task1,not task
                                                    for (QueryDocumentSnapshot snapshot : Objects.requireNonNull(task1.getResult())) {
                                                        Product product = snapshot.toObject(Product.class);
                                                        Log.d(TAG,"All products: " + product.getName());
                                                    }
                                                }
                                        })
                                        .addOnFailureListener(e -> Log.e(TAG,"Error: ",e));
                            }
                    }
                })
                .addOnFailureListener(e -> {
                    vars.verityApp.crashlytics.log("Error while fetching categories");
                    Log.e(TAG,"Error occured: ",e);
                    vars.verityApp.crashlytics.recordException(e);
                });
    }

也许当代码到达时task1还没有完成，并且因为任务实际上已经完成，所以无论如何都会触发