Question

首先，我在很多地方搜索过，但我根本找不到这个问题的答案，所以，我在这里问。但是，我想知道：我如何在Android中的Firebase数据库中转换这样的查询： * SELECT a，b，c FROM MyTable * ？我试过的方法如下：

public void testQueryMethod(final PhisicianHandler handler) {

    final String databaseReference = "CadastroMedico";

    database.getReference(databaseReference)
            .child("mDoctorID")
            .child("mNome")
            .child("mEspecialidade")
            .addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {

                    ArrayList<String> dadosMedico = new ArrayList<>();

                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        dadosMedico.add(snapshot.getValue().toString());
                        System.out.println(snapshot.getValue().toString());
                    }
                    handler.trataMedico(dadosMedico);
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
}

我的整个模特

公共类FirebaseDatabaseModel {

//Creating the instance of the database
private FirebaseDatabase database = FirebaseDatabase.getInstance();

public ArrayList<String> dataRetriever(final ArrayList<String> dadosMedicosRecebidos, final BaseAdapter adapter) {

    final String tableName = "Especialidade";
    final String childToBeOrdered = "NomesEspecialidades";

    database.getReference(tableName).orderByChild(childToBeOrdered)
            .addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {

                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        dadosMedicosRecebidos.add(snapshot.getValue().toString());
                        adapter.notifyDataSetChanged();
                    }
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });

    return dadosMedicosRecebidos;
}

/**
 * This method gets all the registries where specialty is equal to the selected item on the spinner
 */
public void queryMethod(String selectedItem, final PhisicianHandler handler) {

    final String tableName = "CadastroMedico";
    final String childToBeOrdered = "mEspecialidade";

    database.getReference(tableName)
            .orderByChild(childToBeOrdered)
            .equalTo(selectedItem)
            .addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {

                    ArrayList<String> dadosMedico = new ArrayList<>();

                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        dadosMedico.add(snapshot.getValue().toString());
                    }
                    handler.trataMedico(dadosMedico);
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
}

public void userIdQueryMethod(final PhisicianHandler handler) {

    final String tableName = "UserID";
    final String childToBeOrdered = "ID/UserID";

    database.getReference(tableName).orderByChild(childToBeOrdered)
            .addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {

                    ArrayList<String> dadosMedico = new ArrayList<>();

                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        dadosMedico.add(snapshot.getValue().toString());
                    }
                    handler.trataMedico(dadosMedico);
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
}

public void doctorIdQueryMethod(final PhisicianHandler handler) {

    final String tableName = "DoctorID";
    final String childToBeOrdered = "ID/DoctorID";

    database.getReference(tableName).orderByChild(childToBeOrdered)
            .addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {

                    ArrayList<String> dadosMedico = new ArrayList<>();

                    for (DataSnapshot snapshot : dataSnapshot.getChildren()) {
                        dadosMedico.add(snapshot.getValue().toString());
                    }
                    handler.trataMedico(dadosMedico);
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
}

public void testQueryMethod(String specialty, final PhisicianHandler handler) {

    final String tableName = "CadastroMedico";
    final String childToBeOrdered = "mEspecialidade";

    DatabaseReference database = FirebaseDatabase.getInstance().getReference()
            .child("CadastroMedico");

            database.child("mDoctorID")
            .child("mNome")
            .child("mEspecialidade")
            .orderByChild(childToBeOrdered)
            .equalTo(specialty);

            database.addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {

                    ArrayList<String> dadosMedico = new ArrayList<>();

                    for (DataSnapshot snapshot : 
            dataSnapshot.getChildren()) {

            dadosMedico.add(snapshot.getValue().toString());                           
            System.out.println(snapshot.getValue().toString());

                }
                    handler.trataMedico(dadosMedico);
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, 
                String prevChildKey) {
                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {
                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, 
                    String prevChildKey) {
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                }
            });
}

}

但它对我不起作用。当我尝试在日志窗口中显示它时，我收到此消息：I / System.out：propertyValue：false并且我没有从我的基础获取任何值。我将添加一个图像，以便您可以看到我在说什么。

Image 1: The fields i'm talking about

Document: Screenshots of my whole database

我想做的是（例如在SQL中）： * SELECT mDoctorID，mEmail，mEndereço来自CadastroMedico; *

我认为这是可能的，但我不知道该怎么做。我会很感激一些关于它的想法。提前谢谢。

Answer 1

试试这个

DatabaseReference mDatabase=FirebaseDatabase.getInstance().getReference().child("CadastroMedico");
        mDatabase.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String prevChildKey) {

                String doctorID=dataSnapshot.child("mDoctorId").getValue(String.class);
                String mNome=dataSnapshot.child("mNome").getValue(String.class);
                handler.trataMedico(dadosMedico);
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String prevChildKey) {
            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {
            }

            @Override
            public void onChildMoved(DataSnapshot dataSnapshot, String prevChildKey) {
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });

Answer 2

创建一个类并声明要从其中的firebase获取的所有变量。在您的情况下，它们将是mDoctorID，mNome和mEspecialidade。
在课程关键字

@IgnoreExtraProperties

确保变量的名称与Firebase中的节点名称完全相同。它将如下所示：

@IgnoreExtraProperties
class CadastroMedico{
    public String mDoctorID="", mNome="", mEspecialidade="";
}

现在调用firebase数据库查询，如果只想使用addListenerForSingleValueEvent一次获取数据。假设您只需要一次数据，因为SELECT查询也只返回一次数据，代码看起来像这样：

reference.addListenerForSingleValueEvent(new ValueEventListener(){
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        List<CadastroMedico> dadosMedico = new ArrayList();
        for (DataSnapshot snapshot : dataSnapshot.getChildren()){
            CadastroMedico cadastroMedico = snapshot.getValue(CadastroMedico.class)
            dadosMedico.add(cadastroMedico);
            System.out.println(cadastroMedico.mDoctorID + " " + cadastroMedico.mNome + " " +cadastroMedico.mEspecialidade);
        }
        //modify your handler accordingly
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        //handle error
    }});

如何在Android中的Firebase数据库中执行具有多个字段的SELECT？

2 个答案: