如何在android中查询Firestore并获取特定文档

Question

我在使用firestore查询“wherequalto”时遇到了麻烦。我试图从一个名为“参与者”的集合中获取图像，但当文档不存在时，应该使用else语句并移动到更新文档的下一个活动。但是在onComplete侦听器（即任务）中从集合中查询文档时，文档没有退出，而是代码运行到if（Task.issucessful）{}中，并且没有使用else语句。我的代码：有谁能帮我吗？谢谢

 //***********BattlePost1**************

        mFirestore.collection("OpenBattle")
                .document(battlesPost_creator)
                .collection("BattlePost")
                .document(battlePost_id)
                .collection("Participants")
                .document(UserId)
                .collection("Posts").whereEqualTo("battle_post_count", 1)
                .get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()){
                    for (QueryDocumentSnapshot document : task.getResult()){
                        Glide.with(mContext).load(document.get("imageuri")).into(battle_creator_postImage1);
                        battle_points1.setText(String.valueOf(document.get("numberOfLikesPoints")) + "Points");
                    }

                }else {
                    Log.d(TAG, "onComplete: Error getting the first document");
                }
            }
        });

        //**************BattlePost2***************

        mFirestore.collection("OpenBattle")
                .document(battlesPost_creator)
                .collection("BattlePost")
                .document(battlePost_id)
                .collection("Participants")
                .document(UserId)
                .collection("Posts")
                .whereEqualTo("battle_post_count", 2)
                .get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()) {
                    for (QueryDocumentSnapshot document : task.getResult()) {
                        Log.d(TAG, document.getId() + " => " + document.getData());
                        Glide.with(mContext).load(document.get("imageuri")).into(battle_creator_postImage2);
                        battle_points2.setText(String.valueOf(document.get("numberOfLikesPoints")) + "Points");
                    }
                } else {
                    Log.d(TAG, "Error getting documents: ", task.getException());
                    //Can create a 2nd post
                    Glide.with(mContext).load(R.drawable.ic_add_circle_black_24dp).into(battle_creator_postImage2);
                    battle_creator_postImage2.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            Intent intent = new Intent(mContext, TemplateActivity.class);
                            intent.putExtra(getString(R.string.battle_add_post),battlePost_id);
                            intent.putExtra("BattlePost_Pub", battlesPost_creator);
                            intent.putExtra("Battle_contest", 2);
                            intent.putExtra("Battle_tittle", battle_tittle);
                            intent.putExtra("Battle_timeEnd", battle_timeEnd);
                            startActivity(intent);
                        }
                    });
                }
            }
        });

Answer 1

即使找不到文档，task.issucesful()也会返回true，因为它已经完成了查询的任务，并且发现不存在这样的文档。因此，您应该检查文档是否存在。从文档中看一下-

DocumentReference docRef = db.collection("cities").document("SF");
docRef.get().addOnCompleteListener(new OnCompleteListener<DocumentSnapshot>() {
    @Override
    public void onComplete(@NonNull Task<DocumentSnapshot> task) {
        if (task.isSuccessful()) {
            DocumentSnapshot document = task.getResult();
            //See the part below.
            if (document.exists()) {
                Log.d(TAG, "DocumentSnapshot data: " + document.getData());
            } else {
                Log.d(TAG, "No such document");
            }
        } else {
            Log.d(TAG, "get failed with ", task.getException());
        }
    }
});

您将必须编写另一个else语句，并将用于更新文档的代码放入其中。