作者:fanersai_668 | 来源:互联网 | 2023-02-10 20:01
我目前正在使用Firebase编写Android应用程序.我有一个具有城市属性的产品型号.我正在运行以下查询:
mDatabaseReference = FirebaseDatabase.getInstance().getReference();
mDatabaseReference.keepSynced(true);
productQuery = mDatabaseReference.child("products")
.orderByChild("city").equalTo(mCurrentUser).limitToFirst(100);
无论城市如何,此查询都会检索数据库中的所有产品.
我花了最后四个小时审查关于SO的类似问题,并尝试查询函数的不同组合+规则索引无济于事.我有一个我称之为愚蠢的解决方案,它重新复制城市产品树下的数据.但是我猜测有一个更好的方法来利用orderByChild,如果我能得到一些帮助来查询城市数据,我将不胜感激.
感谢您的输入
这是CityFeed片段 - 注意:我检查了mCurrentUserCity已设置
public class CityFeedFragment extends BaseFragment {
private RecyclerView mRecyclerView;
private String mCurrentUserCity;
private FirebaseProductAdapter mAdapter;
private DatabaseReference mDatabaseReference;
private LinearLayoutManager mManager;
private Query productQuery;
private SwipeRefreshLayout mSwipeRefreshLayout;
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_feed, container, false);
mDatabaseReference = FirebaseDatabase.getInstance().getReference();
mDatabaseReference.keepSynced(true);
retrieveCity();
fetchProducts();
mAdapter = new FirebaseProductAdapter(Product.class,
R.layout.feed_item, ProductViewHolder.class,
productQuery.getRef(), getContext(), false);
return view;
}
@Override
public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
mSwipeRefreshLayout = (SwipeRefreshLayout) view.findViewById(R.id.swipe_refresh_layout);
mRecyclerView.setAdapter(mAdapter);
mManager = new LinearLayoutManager(getActivity());
mManager.setReverseLayout(true);
mManager.setStackFromEnd(true);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setItemAnimator(new DefaultItemAnimator());
mRecyclerView.setLayoutManager(mManager);
mSwipeRefreshLayout.setOnRefreshListener(() -> {
fetchProducts();
mAdapter.notifyDataSetChanged();
mSwipeRefreshLayout.setRefreshing(false);
});
}
private void fetchProducts() {
productQuery = mDatabaseReference.child("products").orderByChild("city").equalTo(mCurrentUserCity);
}
private void retrieveCity() {
mDatabaseReference.child("users").child(getUid()).addListenerForSingleValueEvent(
new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
User user = dataSnapshot.getValue(User.class);
if (user == null) {
showToast(getResources().getString(R.string.empty_user));
} else {
mCurrentUserCity = user.getCity();
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
showToast(databaseError.toString());
Log.w("Cityfeed", "getUser:onCancelled", databaseError.toException());
}
}
);
}
}
数据结构
1> brijesh kuma..:
除了添加用于将值作为数据快照的侦听器之外,您已经完成了所有操作.请用这个替换你的方法 -
private void fetchProducts() {
productQuery = mDatabaseReference.child("products").orderByChild("city").equalTo(mCurrentUserCity).addListenerForSingleValueEvent(
new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
//Map of all products which has city equal to mCurrentUserCity
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
}
);
}