Database Relasional
Skala Industri 🗄️

package com.example.cafeapp;

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity(tableName = "tabel_kategori")
public class Kategori {
    @PrimaryKey(autoGenerate = true) 
    public int id;

    @ColumnInfo(name = "nama_kategori") 
    public String namaKategori;
    
    public Kategori(String namaKategori) { 
        this.namaKategori = namaKategori; 
    }
}

package com.example.cafeapp;

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.ForeignKey;
import androidx.room.PrimaryKey;

@Entity(tableName = "tabel_menu",
        foreignKeys = @ForeignKey(entity = Kategori.class,
                                  parentColumns = "id",
                                  childColumns = "kategori_id",
                                  onDelete = ForeignKey.CASCADE))
public class MenuCafe {
    @PrimaryKey(autoGenerate = true) 
    public int id;

    @ColumnInfo(name = "nama_menu") 
    public String namaMenu;

    public int harga;
    public int stok;

    @ColumnInfo(name = "kategori_id") 
    public int kategoriId;

    public MenuCafe(String namaMenu, int harga, int stok, int kategoriId) {
        this.namaMenu = namaMenu; 
        this.harga = harga; 
        this.stok = stok; 
        this.kategoriId = kategoriId;
    }
}

package com.example.cafeapp;

import androidx.room.ColumnInfo;

// BUKAN Entity/Tabel! Hanya class biasa.
public class MenuDetail {
    public int id;

    @ColumnInfo(name = "nama_menu") 
    public String namaMenu;
    
    public int harga;
    public int stok;

    // Kolom ini berasal dari tabel Kategori lho!
    @ColumnInfo(name = "nama_kategori") 
    public String namaKategori;
}

package com.example.cafeapp;

import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import java.util.List;

@Dao
public interface CafeDao {
    
    @Insert 
    void insertKategori(Kategori kategori);
    
    @Insert 
    void insertMenu(MenuCafe menu);

    // Tarik List Data Join (Otomatis mengubahnya menjadi List Object!)
    @Query("SELECT m.id, m.nama_menu, m.harga, m.stok, k.nama_kategori " +
           "FROM tabel_menu m INNER JOIN tabel_kategori k ON m.kategori_id = k.id " +
           "ORDER BY m.id DESC")
    List<MenuDetail> getMenuLengkap();

    // Hapus Berdasarkan ID yang dipilih
    @Query("DELETE FROM tabel_menu WHERE id = :menuId")
    void deleteMenuById(int menuId);
}

package com.example.cafeapp;

import android.content.Context;
import androidx.annotation.NonNull;
import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;
import androidx.sqlite.db.SupportSQLiteDatabase;
import java.util.concurrent.Executors;

// Daftarkan KEDUA tabel di sini!
@Database(entities = {Kategori.class, MenuCafe.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {

    public abstract CafeDao cafeDao();
    private static volatile AppDatabase INSTANCE;

    public static AppDatabase getInstance(Context context) {
        if (INSTANCE == null) {
            synchronized (AppDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE = Room.databaseBuilder(
                        context.getApplicationContext(), AppDatabase.class, "cafe_room.db")
                        // Memasukkan data dummy awal Kategori saat Database baru lahir
                        .addCallback(roomCallback) 
                        .build();
                }
            }
        }
        return INSTANCE;
    }

    private static RoomDatabase.Callback roomCallback = new RoomDatabase.Callback() {
        @Override
        public void onCreate(@NonNull SupportSQLiteDatabase db) {
            super.onCreate(db);
            // Pekerja khusus di awal instalasi aplikasi
            Executors.newSingleThreadExecutor().execute(() -> {
                CafeDao dao = INSTANCE.cafeDao();
                dao.insertKategori(new Kategori("Kopi"));
                dao.insertKategori(new Kategori("Non-Kopi"));
                dao.insertKategori(new Kategori("Cemilan"));
            });
        }
    };
}

package com.example.cafeapp;

import android.os.Handler;
import android.os.Looper;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.List;
import java.util.concurrent.Executors;

public class MenuAdapter extends RecyclerView.Adapter<MenuAdapter.MenuViewHolder> {

    private List<MenuDetail> listMenu;
    private AppDatabase db; // Butuh akses ke DB Induk Room

    public MenuAdapter(List<MenuDetail> listMenu, AppDatabase db) {
        this.listMenu = listMenu;
        this.db = db;
    }

    public void setData(List<MenuDetail> dataBaru) {
        this.listMenu = dataBaru;
        notifyDataSetChanged();
    }

    @NonNull
    @Override
    public MenuViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_menu, parent, false);
        return new MenuViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull MenuViewHolder holder, int position) {
        MenuDetail menu = listMenu.get(position);

        holder.tvJudul.setText(menu.namaMenu);
        holder.tvKategori.setText("Kategori: " + menu.namaKategori);
        holder.tvHargaStok.setText("Rp " + menu.harga + " | Stok: " + menu.stok);

        // LOGIKA HAPUS ROOM (WAJIB BACKGROUND THREAD!)
        holder.btnDelete.setOnClickListener(v -> {
            // 1. Kirim instruksi hapus ke Background
            Executors.newSingleThreadExecutor().execute(() -> {
                
                db.cafeDao().deleteMenuById(menu.id); // Hapus di Database
                listMenu.remove(position);            // Hapus di List Memori Lokal
                
                // 2. Pakai Handler untuk kembali melapor (menelpon) ke UI Thread (Main)
                new Handler(Looper.getMainLooper()).post(() -> {
                    // Animasi Mengerut (Hanya boleh dipanggil di UI Thread!)
                    notifyItemRemoved(position);
                    notifyItemRangeChanged(position, listMenu.size());
                    Toast.makeText(holder.itemView.getContext(), "Dihapus secara pro!", Toast.LENGTH_SHORT).show();
                });
            });
        });
    }

    @Override
    public int getItemCount() { return listMenu.size(); }

    public class MenuViewHolder extends RecyclerView.ViewHolder {
        TextView tvJudul, tvKategori, tvHargaStok;
        ImageButton btnDelete;

        public MenuViewHolder(@NonNull View itemView) {
            super(itemView);
            tvJudul = itemView.findViewById(R.id.tvJudul);
            tvKategori = itemView.findViewById(R.id.tvKategori);
            tvHargaStok = itemView.findViewById(R.id.tvHargaStok);
            btnDelete = itemView.findViewById(R.id.btnDelete);
        }
    }
}

package com.example.cafeapp;

import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class MainActivity extends AppCompatActivity {

    private AppDatabase db;
    private MenuAdapter adapter;
    private ExecutorService executor = Executors.newSingleThreadExecutor();

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

        EditText etNama = findViewById(R.id.etNama);
        EditText etHarga = findViewById(R.id.etHarga);
        EditText etStok = findViewById(R.id.etStok);
        Spinner spKategori = findViewById(R.id.spKategori); 
        Button btnTambah = findViewById(R.id.btnTambah);
        RecyclerView rvMenu = findViewById(R.id.rvMenu);

        // Mengisi data ke dalam Spinner secara aman
        String[] kategoriArr = {"Kopi", "Non-Kopi", "Cemilan"};
        ArrayAdapter<String> spinAdapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_dropdown_item, kategoriArr);
        spKategori.setAdapter(spinAdapter);

        // 1. Siapkan DB Induk dan Pasang Adapter Kosong dulu
        db = AppDatabase.getInstance(this);
        adapter = new MenuAdapter(new ArrayList<>(), db);
        
        rvMenu.setLayoutManager(new LinearLayoutManager(this));
        rvMenu.setAdapter(adapter);

        // Refresh List saat layar dibuka
        refreshDaftarMenu();

        // 2. Saat Tombol Klik Ditekan (INSERT)
        btnTambah.setOnClickListener(v -> {
            String nama = etNama.getText().toString();
            if(nama.isEmpty()) return;
            
            int harga = Integer.parseInt(etHarga.getText().toString());
            int stok = Integer.parseInt(etStok.getText().toString());
            int katId = spKategori.getSelectedItemPosition() + 1;
            
            // WAJIB JALAN DI BACKGROUND!
            executor.execute(() -> {
                
                // Simpan ke Database
                db.cafeDao().insertMenu(new MenuCafe(nama, harga, stok, katId));
                
                // Ambil data terbarunya & Refresh UI lewat RunOnUiThread
                // Harus dipastikan narik data SETELAH insert selesai.
                List<MenuDetail> dataBaru = db.cafeDao().getMenuLengkap();
                runOnUiThread(() -> {
                    adapter.setData(dataBaru);
                    etNama.setText("");
                    etHarga.setText("");
                    etStok.setText("");
                });
            });
        });
    }

    private void refreshDaftarMenu() {
        executor.execute(() -> {
            List<MenuDetail> list = db.cafeDao().getMenuLengkap();
            runOnUiThread(() -> adapter.setData(list));
        });
    }
}