firebase - 从列表中获取单个对象作为快照 [英] firebase - get single object from list as snapshot
问题描述
$ b
最后的FirebaseDatabase数据库= FirebaseDatabase.getInstance() ;
DatabaseReference coutryRef = database.getReference(FireContract.PATH_COUNTRY);
查询countryQuery = coutryRef.orderByChild(FireContract.CHILD_NAME)
.equalTo(TestUtilities.TEST_COUNTRY_ALGERIA).limitToFirst(1);
$ b countryQuery.addListenerForSingleValueEvent(new ValueEventListener(){
@Override $ b $ public void onDataChange(DataSnapshot dataSnapshot){
Country country = dataSnapshot.getValue( Country.class);
assertEquals(TestUtilities.TEST_COUNTRY_ALGERIA,country.getName());
//获取国家/地区代码
字符串coutryKey = dataSnapshot.getKey();
$ b $覆盖$ b $ public void onCancelled(DatabaseError databaseError){
fail(Failed to get country:+ databaseError.getMessage());
}
});
当您启动查询时,结果列表。即使只有一个项目与查询匹配,结果也会是一个项目的列表。
要处理列表,您可以使用 ChildEvenListener
,或者你可以循环 ValueEventListener
中的子元素:
<$ p (DataSnapshot countrySnapshot:dataSnapshot.getChildren())返回值为
的数据类型为
的公共无效onDataChange(DataSnapshot dataSnapshot){
的数据快照countrySnapshot:dataSnapshot.getChildren() ){
Country country = countrySnapshot.getValue(Country.class);
assertEquals(TestUtilities.TEST_COUNTRY_ALGERIA,country.getName());
// get国家密钥
字符串countryKey = countrySnapshot.getKey();
}
}
$ b $ @覆盖
public void onCancelled(DatabaseError databaseError){
失败(无法获得国家:+ databaseError.getMessage());
}
});
So I have a list of objects stored in firebase and want to query for just one object using child equal to method but I am getting a map with single key value instead.
Code below showing what I want to achieve instead of dealing with hashmaps.
final FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference coutryRef = database.getReference(FireContract.PATH_COUNTRY);
Query countryQuery = coutryRef.orderByChild(FireContract.CHILD_NAME)
.equalTo(TestUtilities.TEST_COUNTRY_ALGERIA).limitToFirst(1);
countryQuery.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
Country country = dataSnapshot.getValue(Country.class);
assertEquals(TestUtilities.TEST_COUNTRY_ALGERIA, country.getName());
//get country key
String coutryKey = dataSnapshot.getKey();
}
@Override
public void onCancelled(DatabaseError databaseError) {
fail("Failed to get country: " + databaseError.getMessage());
}
});
When you fire a query, you will always get a list of results. Even when there is only a single item matching the query, the result will be a list of one item.
To handle the list, you can either use a ChildEvenListener
or you can loop over the children in your ValueEventListener
:
countryQuery.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot countrySnapshot: dataSnapshot.getChildren()) {
Country country = countrySnapshot.getValue(Country.class);
assertEquals(TestUtilities.TEST_COUNTRY_ALGERIA, country.getName());
//get country key
String countryKey = countrySnapshot.getKey();
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
fail("Failed to get country: " + databaseError.getMessage());
}
});
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