Question

我已经创建了一个数据库和一个表。现在，我想在数据库中添加另一个表，并在其中添加新表。

df = pd.DataFrame({'col2': [list('abc'), list('de'), list('fghi')]})
flat_col2 = [element for row in df.col2 for element in row]
# ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i']

另一个是：-

package com.example.user.shopkeeper.sql;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

import com.example.user.shopkeeper.model.User;

import java.util.ArrayList;
import java.util.List;

public class DatabaseHelper extends SQLiteOpenHelper {

        private static final int DATABASE_VERSION = 1;
        private static final String DATABASE_NAME = "manager.db";
        private static final String TABLE_USER = "user";

        private static final String COLUMN_USER_ID = "user_id";
        private static final String COLUMN_USER_NAME = "user_name";
        private static final String COLUMN_USER_EMAIL = "user_email";
        private static final String COLUMN_USER_PASSWORD = "user_password";
        private static final String COLUMN_USER_MOBILE_NUMBER = "user_mobile_number";

        private String CREATE_USER_TABLE = "CREATE TABLE " + TABLE_USER + "("
                + COLUMN_USER_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_USER_NAME + " TEXT, "
                + COLUMN_USER_EMAIL + " TEXT, " + COLUMN_USER_PASSWORD + " TEXT, "+  COLUMN_USER_MOBILE_NUMBER + " TEXT" + ")";

        private String DROP_USER_TABLE = "DROP TABLE IF EXISTS " + TABLE_USER;

        public DatabaseHelper(Context context){
            super(context, DATABASE_NAME,null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db){
            db.execSQL(CREATE_USER_TABLE);
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
            db.execSQL(DROP_USER_TABLE);
            onCreate(db);
        }

        public void addUser(User user){
            SQLiteDatabase db = this.getWritableDatabase();
            ContentValues values = new ContentValues();
            values.put(COLUMN_USER_NAME,user.getName());
            values.put(COLUMN_USER_EMAIL,user.getEmail());
            values.put(COLUMN_USER_PASSWORD,user.getPassword());
            values.put(COLUMN_USER_MOBILE_NUMBER,user.getNumber());

            db.insert(TABLE_USER,null,values);
            db.close();
        }

        public boolean checkUser(String email, String password){
            String[] columns = {
                    COLUMN_USER_ID
            };

            SQLiteDatabase db = this.getWritableDatabase();
            String selection = COLUMN_USER_EMAIL + " = ?" + " AND " + COLUMN_USER_PASSWORD + " = ? ";
            String[] selectionArgs = {email , password};

            Cursor cursor = db.query(TABLE_USER,
                    columns,
                    selection,
                    selectionArgs,
                    null,
                    null,
                    null );

            int cursorCount = cursor.getCount();
            cursor.close();
            db.close();

            if(cursorCount > 0){
                return true;
            }
            else{
                return false;
            }

        }


        public boolean checkUser(String email){
            String[] columns = {
                    COLUMN_USER_ID
            };

            SQLiteDatabase db = this.getWritableDatabase();
            String selection = COLUMN_USER_EMAIL + " = ?" ;
            String[] selectionArgs = {email};

            Cursor cursor = db.query(TABLE_USER,
                    columns,
                    selection,
                    selectionArgs,
                    null,
                    null,
                    null );

            int cursorCount = cursor.getCount();
            cursor.close();
            db.close();

            if(cursorCount > 0){
                return true;
            }
            else{
                return false;
            }

        }

        public List<String> getContactNumber(String email){
            List<String> a = new ArrayList<>();
            String[] contact = new String[]{email};
            SQLiteDatabase db = this.getReadableDatabase();
            String query = "SELECT " + COLUMN_USER_MOBILE_NUMBER +", " + COLUMN_USER_ID + ", " +COLUMN_USER_NAME + " FROM " + TABLE_USER + " WHERE " + COLUMN_USER_EMAIL + " =?";
            Cursor c = db.rawQuery(query, contact);

            if(c.moveToFirst()){
                a.add(c.getString(c.getColumnIndex(COLUMN_USER_MOBILE_NUMBER)));
                a.add(c.getString(c.getColumnIndex(COLUMN_USER_NAME)));
                a.add(c.getString(c.getColumnIndex(COLUMN_USER_ID)));

            }

            db.close();
            c.close();
            return a;
        }

}

我想知道如何在现有数据库中添加表。它包括一些要修改的升级部分，我找不到它。我是Android新手，无法搜索正确的代码对其进行修改。

我得到的错误是找不到表客户端。

Answer 1

未找到（将要获得）表的原因是数据库存储在磁盘上，即它是持久性的。它被创建一次。一旦存在，就不会重新创建。因此（不同于活动） onCreate 方法仅在数据库的生命周期内运行一次（除非另外调用，例如，您经常会从onUpgrade方法中看到它）。

因此，您必须相应地设计使用 onCreate 。

在您的情况下，最简单的方法可能是将两个类结合起来，例如

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 2; //<<<<<<<<<< Changed so will call onUpgrade
    private static final String DATABASE_NAME = "manager.db";
    private static final String TABLE_USER = "user";

    private static final String COLUMN_USER_ID = "user_id";
    private static final String COLUMN_USER_NAME = "user_name";
    private static final String COLUMN_USER_EMAIL = "user_email";
    private static final String COLUMN_USER_PASSWORD = "user_password";
    private static final String COLUMN_USER_MOBILE_NUMBER = "user_mobile_number";

    private String CREATE_USER_TABLE = "CREATE TABLE " + TABLE_USER + "("
            + COLUMN_USER_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_USER_NAME + " TEXT, "
            + COLUMN_USER_EMAIL + " TEXT, " + COLUMN_USER_PASSWORD + " TEXT, "+  COLUMN_USER_MOBILE_NUMBER + " TEXT" + ")";

    private String DROP_USER_TABLE = "DROP TABLE IF EXISTS " + TABLE_USER;


    private final static String TABLE_CLIENT = "clients";
    private final static String _ID = BaseColumns._ID;
    //private final static String COLUMN_USER_ID = "user_id";
    private final static String CLIENT_USER_ID = "client_user_id";
    private final static String COLUMN_CLIENT_NAME = "name";
    private final static String COLUMN_CLIENT_GENDER = "gender";
    private final static String COLUMN_CLIENT_MOBILE_NUMBER = "mobile_number";
    private final static String COLUMN_AMOUNT = "amount";
    public final static int GENDER_UNKNOWN = 0;
    public final static int GENDER_MALE = 1;
    public final static int GENDER_FEMALE = 2;

    private String CREATE_CLIENT_TABLE = "CREATE TABLE " + TABLE_CLIENT + "( "
            + CLIENT_USER_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + COLUMN_USER_ID + " INTEGER, "
            + COLUMN_CLIENT_NAME + " TEXT, " + COLUMN_CLIENT_MOBILE_NUMBER + " TEXT, " + COLUMN_CLIENT_GENDER + " TEXT, "
            + COLUMN_AMOUNT + " INTEGER" + " )";

    private String DROP_CLIENT_TABLE = "DROP TABLE IF EXISTS " + TABLE_CLIENT;

    public DatabaseHelper(Context context){
        super(context, DATABASE_NAME,null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db){
        db.execSQL(CREATE_USER_TABLE);
        db.execSQL(CREATE_CLIENT_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion){
        db.execSQL(DROP_USER_TABLE);
        db.execSQL(DROP_CLIENT_TABLE);
        onCreate(db);
    }

    public void addUser(User user){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COLUMN_USER_NAME,user.getName());
        values.put(COLUMN_USER_EMAIL,user.getEmail());
        values.put(COLUMN_USER_PASSWORD,user.getPassword());
        values.put(COLUMN_USER_MOBILE_NUMBER,user.getNumber());

        db.insert(TABLE_USER,null,values);
        db.close();
    }

    public boolean checkUser(String email, String password){
        String[] columns = {
                COLUMN_USER_ID
        };

        SQLiteDatabase db = this.getWritableDatabase();
        String selection = COLUMN_USER_EMAIL + " = ?" + " AND " + COLUMN_USER_PASSWORD + " = ? ";
        String[] selectionArgs = {email , password};

        Cursor cursor = db.query(TABLE_USER,
                columns,
                selection,
                selectionArgs,
                null,
                null,
                null );

        int cursorCount = cursor.getCount();
        cursor.close();
        db.close();

        if(cursorCount > 0){
            return true;
        }
        else{
            return false;
        }
    }

    public boolean checkUser(String email){
        String[] columns = {
                COLUMN_USER_ID
        };

        SQLiteDatabase db = this.getWritableDatabase();
        String selection = COLUMN_USER_EMAIL + " = ?" ;
        String[] selectionArgs = {email};

        Cursor cursor = db.query(TABLE_USER,
                columns,
                selection,
                selectionArgs,
                null,
                null,
                null );

        int cursorCount = cursor.getCount();
        cursor.close();
        db.close();

        if(cursorCount > 0){
            return true;
        }
        else{
            return false;
        }
    }

    public List<String> getContactNumber(String email){
        List<String> a = new ArrayList<>();
        String[] contact = new String[]{email};
        SQLiteDatabase db = this.getReadableDatabase();
        String query = "SELECT " + COLUMN_USER_MOBILE_NUMBER +", " + COLUMN_USER_ID + ", " +COLUMN_USER_NAME + " FROM " + TABLE_USER + " WHERE " + COLUMN_USER_EMAIL + " =?";
        Cursor c = db.rawQuery(query, contact);

        if(c.moveToFirst()){
            a.add(c.getString(c.getColumnIndex(COLUMN_USER_MOBILE_NUMBER)));
            a.add(c.getString(c.getColumnIndex(COLUMN_USER_NAME)));
            a.add(c.getString(c.getColumnIndex(COLUMN_USER_ID)));

        }

        db.close();
        c.close();
        return a;
    }

    public boolean checkUserMobile(String contact){
        String[] columns = {
                CLIENT_USER_ID
        };

        SQLiteDatabase db = this.getReadableDatabase();
        String selection = COLUMN_CLIENT_MOBILE_NUMBER  + " =? ";
        String[] selectionArgs = {contact};
        Cursor cursor = db.query(TABLE_CLIENT,
                columns,
                selection,
                selectionArgs,
                null,
                null,
                null );

        int count = cursor.getCount();
        cursor.close();
        db.close();

        if(count > 0){
            return true;
        } else{
            return false;
        }
    }

    public void addClient(User user){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COLUMN_USER_ID,user.getUserId());
        values.put(COLUMN_CLIENT_NAME,user.getName());
        values.put(COLUMN_CLIENT_MOBILE_NUMBER,user.getNumber());
        values.put(COLUMN_CLIENT_GENDER,user.getGender());
        values.put(COLUMN_AMOUNT,user.getAmount());

        db.insert(TABLE_CLIENT,null,values);
        db.close();
    }
}

请注意注释/// <<<<<<<<<<已更改，因此将调用onUpgrade
- 正如所说的那样，这将导致调用onUpgrade方法，该方法将同时删除两个表和调用onCreate的方法，然后将创建两个表。
- 如果您不想增加数据库版本（例如，在开发应用程序时希望将其保持在1），那么假设您没有要保留的数据，则可以删除该应用程序的数据或卸载该应用程序，然后重新运行。
- 如果您需要保留现有数据，则需要提出另一个问题，因为这超出了此问题的范围（尽管可行）。
您可能会注意到行//private final static String COLUMN_USER_ID = "user_id";已被注释掉，这是因为在两个原始类中都定义了COLUMN_USER_ID。
请注意，已经更改了onUpgrade和onCreate方法，以容纳两个表。

在Android Studio的辅助程序中添加具有其他sqlhelper类文件的新表

1 个答案: