Question

我正在使用firebase数据库，但我是新手。我正在关注此tutorial，

现在，我的问题是，如果电子邮件已存在于数据库中，我该如何查看？如果电子邮件已经存在，则不应将数据添加到db。

 public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getSimpleName();
    private TextView txtDetails;
    private EditText inputName, inputEmail;
    private Button btnSave;
    private DatabaseReference mFirebaseDatabase;
    private FirebaseDatabase mFirebaseInstance;

    private String userId;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Displaying toolbar icon
        getSupportActionBar().setDisplayShowHomeEnabled(true);
        getSupportActionBar().setIcon(R.mipmap.ic_launcher);

        txtDetails = (TextView) findViewById(R.id.txt_user);
        inputName = (EditText) findViewById(R.id.name);
        inputEmail = (EditText) findViewById(R.id.email);
        btnSave = (Button) findViewById(R.id.btn_save);

        mFirebaseInstance = FirebaseDatabase.getInstance();

        // get reference to 'users' node
        mFirebaseDatabase = mFirebaseInstance.getReference("users");

        // store app title to 'app_title' node
        mFirebaseInstance.getReference("app_title").setValue("Realtime");

        // app_title change listener
        mFirebaseInstance.getReference("app_title").addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                Log.e(TAG, "App title updated");

                String appTitle = dataSnapshot.getValue(String.class);

                // update toolbar title
                getSupportActionBar().setTitle(appTitle);
            }

            @Override
            public void onCancelled(DatabaseError error) {
                // Failed to read value
                Log.e(TAG, "Failed to read app title value.", error.toException());
            }
        });



        // Save / update the user
        btnSave.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
               final String name = inputName.getText().toString();
                final String email = inputEmail.getText().toString();

                // Check for already existed userId
                if (TextUtils.isEmpty(userId)) {
                    createUser(name, email);
                } else {
                    updateUser(name, email);
                }


                mFirebaseDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        //Your Logic here
                        for (DataSnapshot eventSnapshot : dataSnapshot.getChildren()) {
                            User mModel = eventSnapshot.getValue(User.class);
                           // Log.e("DATA" ,""+ mModel.getName());

                        }



                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
            }
        });

        toggleButton();
    }

    // Changing button text
    private void toggleButton() {
        if (TextUtils.isEmpty(userId)) {
            btnSave.setText("Save");
        } else {
            btnSave.setText("Update");
        }
    }

    private void filter()
    {

    }
    /**
     * Creating new user node under 'users'
     */
    private void createUser(String name, String email) {
        // TODO
        // In real apps this userId should be fetched
        // by implementing firebase auth
        if (TextUtils.isEmpty(userId)) {
            userId = mFirebaseDatabase.push().getKey();
        }

        User user = new User(name, email);

        mFirebaseDatabase.child(userId).setValue(user);

        addUserChangeListener();
    }

    /**
     * User data change listener
     */
    private void addUserChangeListener() {
        // User data change listener
        mFirebaseDatabase.child(userId).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                User user = dataSnapshot.getValue(User.class);



                if(!dataSnapshot.child("users").child("email").exists())
                {
                    Log.e(TAG, "User not exists");
                }
                else
                {
                    Log.e(TAG, "User exists");
                }

                // Check for null
                if (user == null) {
                    Log.e(TAG, "User data is null!");
                    return;
                }

                Log.e(TAG, "User data is changed!" + user.name + ", " + user.email);

                // Display newly updated name and email
                txtDetails.setText(user.name + ", " + user.email);

                // clear edit text
                inputEmail.setText("");
                inputName.setText("");

                toggleButton();
            }

            @Override
            public void onCancelled(DatabaseError error) {
                // Failed to read value
                Log.e(TAG, "Failed to read user", error.toException());
            }
        });
    }

    private void updateUser(String name, String email) {
        // updating the user via child nodes
        if (!TextUtils.isEmpty(name))
            mFirebaseDatabase.child(userId).child("name").setValue(name);

        if (!TextUtils.isEmpty(email))
            mFirebaseDatabase.child(userId).child("email").setValue(email);
    }
}

Answer 1

内部ValueEventListener（）检查电子邮件地址是否存在试试这个

if(!dataSnapshot.child("users").child("email").exist)

然后插入新值

Answer 2

如果您尝试为阻止用户创建一个规则，并且有2个帐户使用相同的电子邮件，则可以使用firebase中的规则。有准备好的规则。

身份验证 - ＆gt;方法 - ＆gt;按钮功能。

如何检查firebase中的现有数据？

2 个答案: