java - 检查 Firebase 数据库中是否存在特定值

Question

这个问题在这里已经有了答案:





Checking if a particular value exists in the Firebase database

(6 个回答)


2年前关闭。




我正在使用 java 和 Firebase 开发一个 android 应用程序。这是我用于创建用户配置文件并将数据存储在 firebase 数据库中的代码。

package com.eNotification.getnotify;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AlertDialog;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.content.ContentResolver;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.ConnectivityManager;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.text.TextUtils;
import android.view.View;
import android.webkit.MimeTypeMap;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import com.eNotification.getnotify.utils.Utils;
import com.google.android.gms.tasks.Continuation;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.textfield.TextInputEditText;
import com.google.android.material.textfield.TextInputLayout;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.StorageReference;
import com.google.firebase.storage.StorageTask;
import com.google.firebase.storage.UploadTask;
import com.mikhaellopez.circularimageview.CircularImageView;
import com.squareup.picasso.Picasso;
import com.theartofdev.edmodo.cropper.CropImage;
import com.theartofdev.edmodo.cropper.CropImageView;

import java.util.ArrayList;
import java.util.List;

public class MainActivityCreateProfile extends AppCompatActivity {

    private static final int STORAGE_PERMISSION_CODE=1;

    private TextInputLayout dUsername,dRegNo;
    private TextInputEditText dEditUsername,dEditRegNo;
    private CircularImageView dProfileImage;
    private Spinner dCourse;
    private TextView selected;
    private Button dDoneBtn;

    private String uid,email;
    private String select="Select course",maxid,s;
    private Uri selectedImage=null,uri;

    private FirebaseDatabase firebaseDatabase;
    private DatabaseReference databaseReference;
    private StorageReference storageReference;
    private FirebaseStorage firebaseStorage;

    private StorageTask mUploadTask;

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

        firebaseDatabase = FirebaseDatabase.getInstance();
        firebaseStorage = FirebaseStorage.getInstance();
        databaseReference = FirebaseDatabase.getInstance().getReference().child("USERS");
        storageReference = firebaseStorage.getReference("Profile images");

        uid = getIntent().getStringExtra("uid");
        email = getIntent().getStringExtra("email");

        dProfileImage = findViewById(R.id.dProfileImg);
        dUsername = findViewById(R.id.dUsername);
        dRegNo = findViewById(R.id.dRegNo);
        dEditUsername = findViewById(R.id.dEditUsername);
        dEditRegNo = findViewById(R.id.dEditReg);
        selected = findViewById(R.id.course);
        dCourse = findViewById(R.id.dCourse);

        List<String> categories = new ArrayList<>();
        categories.add(0,"Select course");
        categories.add("BCA");
        categories.add("BBA");
        categories.add("BCOM");
        categories.add("BA");

        ArrayAdapter<String> dataAdapter;
        dataAdapter = new  ArrayAdapter(this,android.R.layout.simple_spinner_item,categories);

        dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        dCourse.setAdapter(dataAdapter);
        dCourse.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            //    if (parent.getItemAtPosition(position).equals("Select course")){
              //      Toast.makeText(MainActivityCreateProfile.this, "Select the course", Toast.LENGTH_SHORT).show();
                //} else {
                    selected.setText(parent.getSelectedItem().toString());
                //}
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {
                Toast.makeText(MainActivityCreateProfile.this, "Select a course", Toast.LENGTH_SHORT).show();
            }
        });

        dDoneBtn = findViewById(R.id.dDoneBtn);

        dDoneBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                inputValidation();
            }
        });

        dProfileImage.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (ContextCompat.checkSelfPermission(MainActivityCreateProfile.this,
                        Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) {
                    Toast.makeText(MainActivityCreateProfile.this, "You have already granted permission", Toast.LENGTH_SHORT).show();
                    SelectImage();
                }  else {
                    requestStoragePermission();
                }
            }
        });
    }

    private void requestStoragePermission() {
        if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivityCreateProfile.this, Manifest.permission.READ_EXTERNAL_STORAGE)) {
            new AlertDialog.Builder(this)
                    .setTitle("Permission needed")
                    .setMessage("This Permission is needed for uploading the Image")
                    .setPositiveButton("ok", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            ActivityCompat.requestPermissions(MainActivityCreateProfile.this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, STORAGE_PERMISSION_CODE);
                        }
                    })
                    .setNegativeButton("cancel", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            dialog.dismiss();
                        }
                    })
                    .create().show();
        } else {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, STORAGE_PERMISSION_CODE);
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        if (requestCode == STORAGE_PERMISSION_CODE) {
            if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                Toast.makeText(this, "Permission granted", Toast.LENGTH_SHORT).show();
                SelectImage();
            } else {
                Toast.makeText(this, "Permission denied", Toast.LENGTH_SHORT).show();

            }
        }
    }

    public void SelectImage() {
        CropImage.activity()
                .setGuidelines(CropImageView.Guidelines.ON)
                .setAspectRatio(1,1)
                .start(this);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if (requestCode == CropImage.CROP_IMAGE_ACTIVITY_REQUEST_CODE) {
            CropImage.ActivityResult result = CropImage.getActivityResult(data);
            if (resultCode == RESULT_OK) {
                selectedImage = result.getUri();
                Picasso.get().load(selectedImage).into(dProfileImage);
            } else if (resultCode == CropImage.CROP_IMAGE_ACTIVITY_RESULT_ERROR_CODE) {
                Exception error = result.getError();
            }
        }
    }

    private void inputValidation() {
        ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        if (cm.getActiveNetworkInfo() != null && cm.getActiveNetworkInfo().isConnected()) {
            //Username validation
            if (!Utils.inputValidation(dEditUsername)) {
                Toast.makeText(this, "Enter the username", Toast.LENGTH_SHORT).show();
                return;
            } else if (!Utils.usernameVerify(dEditUsername)) {
                Toast.makeText(this, "A Username should not exceed 15 characters", Toast.LENGTH_SHORT).show();
                return;
            } else {
                dUsername.setErrorEnabled(false);
            }

            //Reg no Validation
            if (!Utils.inputValidation(dEditRegNo)) {
                Toast.makeText(this, "Enter the Register No", Toast.LENGTH_SHORT).show();
                return;
            } else if (!Utils.regNoVerify(dEditRegNo)) {
                Toast.makeText(this, "Enter correct Register No", Toast.LENGTH_SHORT).show();
                return;
            }
            createProfile();
        }else {
            Toast.makeText(this, "Check internet connection", Toast.LENGTH_SHORT).show();
        }
    }

    public String GetFileExtension(Uri uri) {

        ContentResolver contentResolver = getContentResolver();
        MimeTypeMap mimeTypeMap = MimeTypeMap.getSingleton();
        return mimeTypeMap.getExtensionFromMimeType(contentResolver.getType(uri)) ;

    }

    private void createProfile(){
        final String username = dEditUsername.getText().toString();
        final String regNo = dEditRegNo.getText().toString();
        final String course = dCourse.getSelectedItem().toString();
        maxid = databaseReference.push().getKey();

        if (!TextUtils.isEmpty(username) && (!TextUtils.isEmpty(regNo))) {
            if (!course.equals(select)) {
                databaseReference.orderByChild("regNo").equalTo(regNo).addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                            if (dataSnapshot.exists()){
                                Toast.makeText(MainActivityCreateProfile.this, "Reg no. exist", Toast.LENGTH_SHORT).show();
                            } else {
                                s = "https://firebasestorage.googleapis.com/v0/b/getnotify-da5c1.appspot.com/o/Permanent%2Fuser.png?alt=media&token=017d9013-ede2-49c7-b53b-6e96d90e3398";
                                UserDetails userDetails = new UserDetails(s, username, regNo, course, email);
                                databaseReference.child(maxid).setValue(userDetails);
                                Toast.makeText(MainActivityCreateProfile.this, "Upload Successful", Toast.LENGTH_SHORT).show();
                            }
                        }


                    @Override
                    public void onCancelled(@NonNull DatabaseError databaseError) {
                        Toast.makeText(MainActivityCreateProfile.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
                    }
                });
            } else {
                Toast.makeText(this, "Select a course", Toast.LENGTH_SHORT).show();
            }
        } else {
            Toast.makeText(this, "Enter username and Register No.", Toast.LENGTH_SHORT).show();
        }
    }
}

我遇到了一个问题，我想检查数据库中是否已经存在注册号
这是检查的代码。

databaseReference.orderByChild("regNo").equalTo(regNo).addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                            if (dataSnapshot.exists()){
                                Toast.makeText(MainActivityCreateProfile.this, "Reg no. exist", Toast.LENGTH_SHORT).show();
                            } else {
                                s = "https://firebasestorage.googleapis.com/v0/b/getnotify-da5c1.appspot.com/o/Permanent%2Fuser.png?alt=media&token=017d9013-ede2-49c7-b53b-6e96d90e3398";
                                UserDetails userDetails = new UserDetails(s, username, regNo, course, email);
                                databaseReference.child(maxid).setValue(userDetails);
                                Toast.makeText(MainActivityCreateProfile.this, "Upload Successful", Toast.LENGTH_SHORT).show();
                            }
                        }


                    @Override
                    public void onCancelled(@NonNull DatabaseError databaseError) {
                        Toast.makeText(MainActivityCreateProfile.this, databaseError.getMessage(), Toast.LENGTH_SHORT).show();
                    }
                });

代码正常工作。它检测数据库中是否存在该值并显示 Toast 消息 Reg No. 存在。如果该值不存在，它会成功在数据库中创建子项，但它也会显示 Toast 消息 Reg No. 存在而不是上传成功。我对这些概念很陌生，所以如果您知道任何事情，请提供帮助。

Database node

Answer 1

根据侯赛因的回答。 addValueEventListener()每次您的数据库发生更改时都会调用以克服这种情况，您可以调用 addListenerForSingleValueEvent() .哪个会调用一次。

除此之外，实时数据库中没有 Get 选项

databaseReference.orderByChild("regNo").equalTo(regNo)
    .addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            if (dataSnapshot.exists()) {
                //Do what you want to try
            }else{
                //Create New Node in Database
            }
        }

        @Override
            public void onCancelled(DatabaseError databaseError) {

        }
    });