如何筛选Firestore数据？

Question

我的应用程序允许Users创建Charts，它们存储在Firestore数据库中，如下所示：

charts
    > documentKey1 
         > description = "Example description"
         > name = "Chart name 1"
         > uId = user1Id_string
    > documentKey2
         > description = "Another example description"
         > name = "Chart name 2"
         > uId = user2Id_string
    > documentKey3 
         > description = "Example description again"
         > name = "Chart name 3"
         > uId = user1Id_string

每个用户可以有多个图表。目前，我的MainActivity从数据库中检索当前用户的所有图表，按给定的顺序(由用户设置)对它们进行排序，并在片段中的FirebaseRecyclerView中显示它们。

在ViewPager中，MainActivity有2个片段。相关的一个是FragmentMyCharts，它包含：

public class FragmentMyCharts extends FragmentChartsList {

    public FragmentMyCharts() {}

    public Query getQuery(FirebaseFirestore databaseReference,
                                String orderBy,
                                Query.Direction direction) {

            // Specify the query which is used to retrieve this user's charts
            return databaseReference.collection("charts")
                    .whereEqualTo("uid", getUid())
                    .orderBy(orderBy, direction);

    }

}

这是对FragmentChartsList的扩展，如下所示：

public abstract class FragmentChartsList extends Fragment {

    private FirebaseFirestore mDatabaseRef;
    private ChartListAdapter mAdapter;
    private RecyclerView mRecycler;
    private String mOrder = "name", mFilter;
    private Query.Direction mDirection = Query.Direction.DESCENDING;

    private TextView mLoadingList, mEmptyList;


    public FragmentChartsList() {}

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);

        // Inflate layout, and find Recycler View which will hold the list
        View rootView = inflater.inflate(
                R.layout.fragment_charts_list, container, false);

        mRecycler = rootView.findViewById(R.id.charts_list);
        mRecycler.setHasFixedSize(true);

        mLoadingList = rootView.findViewById(R.id.loading_list);
        mEmptyList = rootView.findViewById(R.id.empty_list);

        // Set up Layout Manager, and set Recycler View to use it
        LinearLayoutManager mManager = new LinearLayoutManager(getActivity());
        mManager.setReverseLayout(true);
        mManager.setStackFromEnd(true);
        mRecycler.setLayoutManager(mManager);

        // Connect to the database
        mDatabaseRef = FirebaseFirestore.getInstance();

        setOrderAndFilter(mOrder, mDirection, mFilter);

        return rootView;
    }

    public abstract Query getQuery(FirebaseFirestore databaseReference,
                                   String orderBy,
                                   Query.Direction direction);


    public void setOrderAndFilter(String order, Query.Direction direction, String filterString) {

        mOrder = order;
        mDirection = direction;
        mFilter = filterString;

        Query mChartsQuery = getQuery(mDatabaseRef, mOrder, mDirection);

        // Update recycler options
        FirestoreRecyclerOptions<Chart> recyclerOptions = new FirestoreRecyclerOptions.Builder<Chart>()
                .setQuery(mChartsQuery, Chart.class)
                .build();

        mAdapter = new ChartListAdapter(recyclerOptions, getActivity());
        mAdapter.startListening();

        mRecycler.setAdapter(mAdapter);

        mChartsQuery.addSnapshotListener(new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(@Nullable QuerySnapshot queryDocumentSnapshots, @Nullable FirebaseFirestoreException e) {

                if (queryDocumentSnapshots != null) {

                    // Hide "loading lists" text
                    mLoadingList.setVisibility(View.GONE);

                    if(queryDocumentSnapshots.size() > 0) {
                        mEmptyList.setVisibility(View.GONE);
                        mRecycler.setVisibility(View.VISIBLE);
                    }else {
                        // If number of Charts = 0,
                        //    if we have filtered, show "no results"
                        //    otherwise, show "no charts"
                        mEmptyList.setVisibility(View.VISIBLE);
                        mRecycler.setVisibility(View.GONE);
                    }
                }

            }
        });

    }

它引用ChartListAdapter类，该类的定义如下：

public class ChartListAdapter extends FirestoreRecyclerAdapter<Chart, ChartViewHolder> {

    private Activity mActivity;

    public ChartListAdapter(FirestoreRecyclerOptions<Chart> recyclerOptions, Activity activity) {
        super(recyclerOptions);

        mActivity = activity;

    }

    @Override
    protected void onBindViewHolder(@NonNull ChartViewHolder holder, int position, @NonNull Chart model) {

        final String chartKey = this.getSnapshots().getSnapshot(position).getId();

        model.setKey(chartKey);

        // Set click listener for the chart
        // On click, the user can view the chart
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(mActivity, ActivityViewChart.class);
                intent.putExtra("ChartKey", chartKey);
                mActivity.startActivity(intent);
            }
        });

        // Implement long-click menu
        mActivity.registerForContextMenu(holder.itemView);

        // Bind Chart to ViewHolder
        holder.bindToChart(model);
    }

    @NonNull
    @Override
    public ChartViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_chart, parent, false);

        return new ChartViewHolder(view);
    }

}

因此，目前这将检索当前用户的所有图表，并对其进行排序和显示。我希望能够做的是过滤结果，以便用户可以输入一些搜索文本，并且只显示其名称或描述包含该文本的图表。

我的理解是，我不能将此作为Firestore查询的一部分，因此我的想法是检索完整的图表列表，然后循环遍历所有图表，删除任何不符合条件的图表，然后显示其余的图表(列表中不太可能有数百个图表；大多数用户只有10个左右)。

我不知道该怎么做，我甚至不确定这是不是最好的方法。最明显的地方似乎是当我在FragmentChartsList中将snapshotListener添加到ChartsQuery中时，但我找不到从列表中删除单个快照的方法。或者，我是否可以将所有项目放入recyclerView中，然后删除不需要的项目？

有谁能给我指个方向吗？我在网上找到的所有东西似乎都是关于删除一个recyclerView项目并将其从数据库中删除，这是我不想做的。

Answer 1

您可以将以下查询用于搜索筛选器功能。

databaseReference.collection("charts")
                 .whereEqualTo("uid", getUid())
                 .orderBy("name")
                 .startAt(searchText)
                 .endAt(searchtText + "\uf8ff");

将搜索文本传递给startAt()和endAt()函数，名称是您的documentField。

并将此查询传递给firestoreAdapter，它将为您提供结果记录。