SQLitedatabase每个用户名都有相同的列表

时间：2013-04-23 00:11:52

标签： android listview sqlite

在我的应用程序的数据库中，我有两个表，一个名为“PLAYERS”，其中包含每个用户的数据和“FRIENDSLIST”，它是每个注册帐户的个人“朋友”列表。如何进程在我的应用程序中进行是当玩家（Joe）注册用户名时，他的信息进入“玩家”表，现在他可以进入我的FindFriends活动，在应用中搜索他朋友的用户名（Bob），然后点击ADD按钮。

然后朋友（Bob）被添加到“FRIENDSLIST”表中。当他进入PlayAFriend活动时，列表将加载显示他添加的“朋友”。所有这一切都很好，直到我意识到当我登录他的朋友的一个帐户（Bob），该朋友的名单与（Joe）相同。

我知道我用来加载（Joe）朋友列表的光标是我用来加载（Bob）朋友列表的光标，所以我问的问题是，< / p>

我如何让乔和鲍勃有他们自己的朋友名单？

我已经尝试在这个网站上搜索并谷歌搜索任何关于如何实现这一点的例子，但我觉得很疯狂，我没有找到关于这个主题的任何教程或帖子，即使每种方法都使用这种类型的练习流行的应用程序。对于长篇文章，我知道这不是一个简单的问题所以这就是为什么我必须详细解释问题所在。

我正在发布我的DBAdapter类，以显示我是如何使用它以及我的PlayAFriend类来显示我的Cursor和ListView。

DBAdapter类

package com.fullfrontalgames.numberfighter;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter {
    static final String KEY_ROWID = "_id";

    static final String KEY_USERNAME = "USERNAME";

    static final String KEY_PASSWORD = "PASSWORD";

    static final String KEY_EMAIL = "EMAIL";

    static final String KEY_NUMBERINPUT = "NUMBERINPUT";

    static final String KEY_SCORE = "SCORE";

    static final String KEY_FRIENDS = "FRIENDS";

    static final String TAG = "DBAdapter";

    static final String DATABASE_NAME = "NFDatabase";

    static final String DATABASE_TABLE1 = "PLAYERS";

    static final String DATABASE_TABLE2 = "FRIENDSLIST";

    static final int DATABASE_VERSION = 4;

    static final String DATABASE_CREATE_TABLE1 = "create table PLAYERS ( _id integer primary key autoincrement, "
            + "USERNAME text not null unique,PASSWORD text not null,EMAIL text,NUMBERINPUT text,SCORE text);";

    static final String DATBASE_CREATE_TABLE2 = "create table FRIENDSLIST (_id integer primary key autoincrement,"
            + "FRIENDS text not null,USERNAME text ,NUMBERINPUT text,SCORE text);";

    final Context context;

    DatabaseHelper DBHelper;

    static SQLiteDatabase db;

    public DBAdapter(Context ctx) {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper {

        public DatabaseHelper(Context context) {
            // TODO Auto-generated constructor stub
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            // TODO Auto-generated method stub
            try {
                db.execSQL(DATABASE_CREATE_TABLE1);
                db.execSQL(DATBASE_CREATE_TABLE2);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            // TODO Auto-generated method stub
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion
                    + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS PLAYERS");
            db.execSQL("DROP TABLE IF EXISTS FRIENDSLIST");
            onCreate(db);
        }

    }

    public DBAdapter open() throws SQLiteException {
        db = DBHelper.getWritableDatabase();
        return this;
    }

    public void close() {
        DBHelper.close();
    }

    // PLAYERS TABLE CRUD

    public long insertPlayer(String Username, String Password, String Email) {
        ContentValues initialValues = new ContentValues();
        initialValues.put("USERNAME", Username);
        initialValues.put("PASSWORD", Password);
        initialValues.put("EMAIL", Email);

        db.insert("PLAYERS", null, initialValues);

        return db.insertWithOnConflict("PLAYERS", null, initialValues,
                SQLiteDatabase.CONFLICT_IGNORE);
    }

    public boolean deletePlayer(long id) {
        Log.d(TAG, "delete is working");
        return db.delete("PLAYERS", KEY_ROWID + " = " + id, null) > 0;

    }

    public Cursor getAllPlayers() {
        return db.query(false, "Players", new String[] {
                "_id", "USERNAME", "PASSWORD", "EMAIL"
        }, null, null, null, null, null, null);

    }

    public String getData() {
        String[] columns = new String[] {
                "_id", "USERNAME", "PASSWORD"
        };
        Cursor mCursor = db.query("PLAYERS", columns, null, null, null, null, null);
        String result = "";
        int iRow = mCursor.getColumnIndex(KEY_ROWID);
        int iName = mCursor.getColumnIndex(KEY_USERNAME);

        for (mCursor.moveToFirst(); !mCursor.isAfterLast(); mCursor.moveToNext()) {
            result = mCursor.getString(iRow) + " " + mCursor.getString(iName) + "/n";
        }
        return result;
    }

    public Cursor getPlayer(int _id) throws SQLException {
        Cursor mCursor = db.query(true, "PLAYERS", new String[] {
                "_id", "USERNAME"
        }, KEY_ROWID + " =  " + "_id", null, null, null, null, null);
        while (mCursor.moveToNext()) {
            int id = mCursor.getInt(mCursor.getColumnIndex("_id"));
        }
        return mCursor;
    }

    public String getUsername(String Username) {
        Cursor mCursor = db.query("Players", new String[] {
            "USERNAME"
        }, "USERNAME = ?", new String[] {
            Username
        }, null, null, null);
        if (mCursor.moveToNext())
            return mCursor.getString(0);
        else
            return "";
    }

    public String getSinlgeEntry(String Username) {
        Cursor cursor = db.query("PLAYERS", null, " USERNAME=?", new String[] {
            Username
        }, null, null, null);
        if (cursor.getCount() < 1) // UserName Not Exist
        {
            cursor.close();
            return "NOT EXIST";
        }
        cursor.moveToFirst();
        String password = cursor.getString(cursor.getColumnIndex("PASSWORD"));
        cursor.close();
        return password;
    }

    public boolean updatePlayer(long _id, String Username, String Password, String Email) {
        ContentValues args = new ContentValues();
        args.put("USERNAME", Username);
        args.put("PASSWORD", Password);
        args.put("EMAIL", Email);
        return db.update("PLAYERS", args, KEY_ROWID + " = " + _id, null) > 0;
    }

    // FRIENDS TABLE CRUD

    public void insertFriend(String Friend) {
        ContentValues initialValues = new ContentValues();
        initialValues.put("FRIENDS", Friend);
        db.insert("FRIENDSLIST", null, initialValues);
    }

    public boolean deleteFriend() {
        return db.delete("FRIENDSLIST", KEY_ROWID + " = " + "_id", null) > 0;
    }

    public Cursor getAllFriends() {
        return db.query(false, "FRIENDSLIST", new String[] {
                "_id", "FRIENDS"
        }, null, null, null, null, null, null);
    }

    public Cursor getFriend(long rowid) throws SQLException {
        Cursor mCursor = db.query(true, "FRIENDSLIST", new String[] {
                "_id", "FRIENDS"
        }, KEY_ROWID + " =  " + "_id", null, null, null, null, null);
        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;
    }

    public boolean updateFriend(long _id, String Friends) {
        ContentValues args = new ContentValues();
        args.put("FRIENDS", Friends);

        return db.update("FRIENDSLIST", args, KEY_ROWID + " = " + _id, null) > 0;
    }

}

PlayAFriend Class 

package com.fullfrontalgames.numberfighter;

import android.app.ListActivity;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.TextView;

public class PlayAFriend extends ListActivity {

    DBAdapter DBAdapter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.playafriend);

        final DBAdapter db = new DBAdapter(this);
        DBAdapter = db.open();

        getListView().setAdapter(new FriendsListAdapter(this, db.getAllFriends()));

    }

    private class FriendsListAdapter extends BaseAdapter implements OnClickListener, ListAdapter {
        private Cursor fFriends;

        private Context fContext;

        public FriendsListAdapter(Context context, Cursor friends) {
            // TODO Auto-generated constructor stub
            fContext = context;
            fFriends = friends;
        }

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return fFriends.getCount();
        }

        @Override
        public FriendInfo getItem(int position) {
            // TODO Auto-generated method stub
            if (fFriends.moveToPosition(position)) {
                String name = fFriends.getString(fFriends.getColumnIndex("FRIENDS"));

                return new FriendInfo(name);
            }
            return null;
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            fFriends.moveToPosition(position);
            return fFriends.getLong(fFriends.getColumnIndex("_id"));
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
            if (convertView == null) {
                convertView = LayoutInflater.from(fContext).inflate(R.layout.playafriendlistitems,
                        parent, false);
            }
            FriendInfo friendinfo = getItem(position);
            TextView friendTV = ViewHolder.get(convertView, R.id.textview_friends);
            Button playbutton = ViewHolder.get(convertView, R.id.playbutton, position);
            playbutton.setOnClickListener(this);

            friendTV.setText(friendinfo.getName());

            return convertView;
        }

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            DBAdapter db = new DBAdapter(fContext);
            db.open();
            int position = (Integer)v.getTag();
            fFriends.moveToPosition(position);
            long id = fFriends.getLong(fFriends.getColumnIndex("_id"));
            fFriends = db.getAllFriends();
            db.close();
        }

    }

}

新的DBAdapter 

package com.fullfrontalgames.numberfighter;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBAdapter {
    static final String KEY_ROWID = "_id";

    static final String KEY_USERNAME = "USERNAME";

    static final String KEY_PASSWORD = "PASSWORD";

    static final String KEY_EMAIL = "EMAIL";

    static final String KEY_NUMBERINPUT = "NUMBERINPUT";

    static final String KEY_SCORE = "SCORE";

    static final String KEY_FRIENDS = "FRIENDS";

    static final String TAG = "DBAdapter";

    static final String DATABASE_NAME = "NFDatabase";

    static final String DATABASE_TABLE1 = "PLAYERS";

    static final String DATABASE_TABLE2 = "FRIENDSLIST";

    static final int DATABASE_VERSION = 9;

    static final String DATABASE_CREATE_TABLE1 = "create table PLAYERS ( _id integer primary key autoincrement, "
            + "USERNAME text not null unique,PASSWORD text not null,EMAIL text,NUMBERINPUT text,SCORE text);";

    static final String DATBASE_CREATE_TABLE2 = "create table FRIENDSLIST (_id integer primary key autoincrement,"
            + "player_id integer not null references PLAYERS(_id) on update cascade on delete cascade,"
            + "FRIENDS text ,NUMBERINPUT text,SCORE text);";

    final Context context;

    DatabaseHelper DBHelper;

    static SQLiteDatabase db;

    public DBAdapter(Context ctx) {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }

    private static class DatabaseHelper extends SQLiteOpenHelper {

        public DatabaseHelper(Context context) {
            // TODO Auto-generated constructor stub
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            // TODO Auto-generated method stub
            try {
                db.execSQL(DATABASE_CREATE_TABLE1);
                db.execSQL(DATBASE_CREATE_TABLE2);
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            // TODO Auto-generated method stub
            Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion
                    + ", which will destroy all old data");
            db.execSQL("DROP TABLE IF EXISTS PLAYERS");
            db.execSQL("DROP TABLE IF EXISTS FRIENDSLIST");
            onCreate(db);
        }

    }

    public DBAdapter open() throws SQLiteException {
        db = DBHelper.getWritableDatabase();
        db.execSQL("PRAGMA foreign_keys=ON;");
        return this;
    }

    public void close() {
        DBHelper.close();
    }

    // PLAYERS TABLE CRUD

    public long insertPlayer(String Username, String Password, String Email) {
        ContentValues initialValues = new ContentValues();
        initialValues.put("USERNAME", Username);
        initialValues.put("PASSWORD", Password);
        initialValues.put("EMAIL", Email);

        db.insert("PLAYERS", null, initialValues);

        return db.insertWithOnConflict("PLAYERS", null, initialValues,
                SQLiteDatabase.CONFLICT_IGNORE);
    }

    public boolean deletePlayer(long id) {
        Log.d(TAG, "delete is working");
        return db.delete("PLAYERS", KEY_ROWID + " = " + id, null) > 0;

    }

    public Cursor getAllPlayers() {
        return db.query(false, "Players", new String[] {
                "_id", "USERNAME", "PASSWORD", "EMAIL"
        }, null, null, null, null, null, null);

    }

    public String getData() {
        String[] columns = new String[] {
                "_id", "USERNAME", "PASSWORD"
        };
        Cursor mCursor = db.query("PLAYERS", columns, null, null, null, null, null);
        String result = "";
        int iRow = mCursor.getColumnIndex(KEY_ROWID);
        int iName = mCursor.getColumnIndex(KEY_USERNAME);

        for (mCursor.moveToFirst(); !mCursor.isAfterLast(); mCursor.moveToNext()) {
            result = mCursor.getString(iRow) + " " + mCursor.getString(iName) + "/n";
        }
        return result;
    }

    public Cursor getPlayer(int _id) throws SQLException {
        Cursor mCursor = db.query(true, "PLAYERS", new String[] {
                "_id", "USERNAME"
        }, KEY_ROWID + " =  " + "_id", null, null, null, null, null);
        while (mCursor.moveToNext()) {
            int id = mCursor.getInt(mCursor.getColumnIndex("_id"));
        }
        return mCursor;
    }

    public String getUsername(String Username) {
        Cursor mCursor = db.query("Players", new String[] {
            "USERNAME"
        }, "USERNAME = ?", new String[] {
            Username
        }, null, null, null);
        if (mCursor.moveToNext())
            return mCursor.getString(0);
        else
            return "";
    }

    public String getSinlgeEntry(String Username) {
        Cursor cursor = db.query("PLAYERS", null, " USERNAME=?", new String[] {
            Username
        }, null, null, null);
        if (cursor.getCount() < 1) // UserName Not Exist
        {
            cursor.close();
            return "NOT EXIST";
        }
        cursor.moveToFirst();
        String password = cursor.getString(cursor.getColumnIndex("PASSWORD"));
        cursor.close();
        return password;
    }

    public boolean updatePlayer(long _id, String Username, String Password, String Email) {
        ContentValues args = new ContentValues();
        args.put("USERNAME", Username);
        args.put("PASSWORD", Password);
        args.put("EMAIL", Email);
        return db.update("PLAYERS", args, KEY_ROWID + " = " + _id, null) > 0;
    }

    // FRIENDS TABLE CRUD

    public void insertFriend(long playerId, String Friend) {
        ContentValues initialValues = new ContentValues();
        initialValues.put("player_id", playerId);
        initialValues.put("FRIENDS", Friend);
        db.insertWithOnConflict("FRIENDSLIST", null, initialValues, SQLiteDatabase.CONFLICT_IGNORE);
    }

    public boolean deleteFriend() {
        return db.delete("FRIENDSLIST", KEY_ROWID + " = " + "_id", null) > 0;
    }

    public Cursor getAllFriends() {
        return db.query(false, "FRIENDSLIST", new String[] {
                "_id", "FRIENDS"
        }, null, null, null, null, null, null);
    }

    public Cursor getFriend(long player_id) throws SQLException {
        Cursor mCursor = db.query(true, "FRIENDSLIST", new String[] {
                "_id", "FRIENDS"
        }, "player_id" + " =  " + "player_id", null, null, null, null, null);
        // cursor from query is never null,
        // should just check for if (cursor.moveToFirst()) in the calling
        // activity
        return mCursor;
    }

    public boolean updateFriend(long _id, String Friends) {
        ContentValues args = new ContentValues();
        args.put("FRIENDS", Friends);

        return db.update("FRIENDSLIST", args, KEY_ROWID + " = " + _id, null) > 0;
    }

    public long getPlayerId(String Username) {
        // TODO Auto-generated method stub
        long id = 0;
        Cursor c = db.query("PLAYERS", new String[] {
            KEY_ROWID
        }, KEY_USERNAME + "=?", new String[] {
            Username
        }, null, null, null);
        if (c.moveToFirst()) {
            id = c.getLong(0);
        }
        c.close();
        return id;
    }

}


New PlayAFriend




package com.fullfrontalgames.numberfighter;

import android.app.ListActivity;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.TextView;

public class PlayAFriend extends ListActivity {

    DBAdapter DBAdapter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.playafriend);

        final DBAdapter db = new DBAdapter(this);
        DBAdapter = db.open();

        long player_id = 0;
        getListView().setAdapter(new FriendsListAdapter(this, db.getFriend(player_id)));

    }

    private class FriendsListAdapter extends BaseAdapter implements OnClickListener, ListAdapter {
        private static final long player_id = 0;

        private Cursor fFriends;

        private Context fContext;

        public FriendsListAdapter(Context context, Cursor friends) {
            // TODO Auto-generated constructor stub
            fContext = context;
            fFriends = friends;
        }

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return fFriends.getCount();
        }

        @Override
        public FriendInfo getItem(int position) {
            // TODO Auto-generated method stub
            if (fFriends.moveToPosition(position)) {
                String name = fFriends.getString(fFriends.getColumnIndex("FRIENDS"));

                return new FriendInfo(name);
            }
            return null;
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            fFriends.moveToPosition(position);
            return fFriends.getLong(fFriends.getColumnIndex("_id"));
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub
            if (convertView == null) {
                convertView = LayoutInflater.from(fContext).inflate(R.layout.playafriendlistitems,
                        parent, false);
            }
            FriendInfo friendinfo = getItem(position);
            TextView friendTV = ViewHolder.get(convertView, R.id.textview_friends);
            Button playbutton = ViewHolder.get(convertView, R.id.playbutton, position);
            playbutton.setOnClickListener(this);

            friendTV.setText(friendinfo.getName());

            return convertView;
        }

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            DBAdapter db = new DBAdapter(fContext);
            db.open();
            int position = (Integer)v.getTag();
            fFriends.moveToPosition(position);
            long id = fFriends.getLong(fFriends.getColumnIndex("_id"));
            fFriends = db.getFriend(id);
            db.close();
        }

    }

}

FindFriends活动

package com.fullfrontalgames.numberfighter;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.FrameLayout;
import android.widget.TextView;
import android.widget.Toast;

public class Findfriends extends Activity {
    DBAdapter db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.findfriends);

        final EditText sbar = (EditText)findViewById(R.id.PlayerSeachBar);
        Button search = (Button)findViewById(R.id.Search);
        Button Add = (Button)findViewById(R.id.Add);
        final TextView ResultText = (TextView)findViewById(R.id.ResultTextView);
        final FrameLayout ResultFrame = (FrameLayout)findViewById(R.id.ResultFrameLayout);

        ResultFrame.setVisibility(View.GONE);

        final DBAdapter db = new DBAdapter(this);
        db.open();

        search.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String Username = sbar.getText().toString();
                String foundplayer = db.getUsername(Username);

                if (Username.equals(foundplayer)) {

                    ResultFrame.setVisibility(View.VISIBLE);
                    ResultText.setText(foundplayer);
                    Toast.makeText(getApplicationContext(), "Player Found", Toast.LENGTH_LONG)
                            .show();

                } else {
                    Toast.makeText(getApplicationContext(), "Username Not Found", Toast.LENGTH_LONG)
                            .show();
                }
            }

        });

        Add.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                String Friends = sbar.getText().toString();
                long playerId = db.getPlayerId(Friends);
                db.insertFriend(playerId, Friends);
                Toast.makeText(getApplicationContext(), "Player Has Been Added", Toast.LENGTH_LONG)
                        .show();

            }
        });
    }
}

logcat的

 04-22 21:11:37.834: E/SQLiteDatabase(15862): Error inserting player_id=0 FRIENDS=null
    04-22 21:11:37.834: E/SQLiteDatabase(15862): android.database.sqlite.SQLiteConstraintException: foreign key constraint failed (code 19)
    04-22 21:11:37.834: E/SQLiteDatabase(15862):    at android.database.sqlite.SQLiteConnection.nativeExecuteForLastInsertedRowId(Native Method)
    04-22 21:11:37.834: E/SQLiteDatabase(15862):    at android.database.sqlite.SQLiteConnection.executeForLastInsertedRowId(SQLiteConnection.java:775)

1 个答案:

答案 0 :(得分：1)

更改您的表格FRIENDSLIST 

static final String DATBASE_CREATE_TABLE2 = 
    "create table FRIENDSLIST (_id integer primary key autoincrement,"
    + "player_id integer not null references PLAYERS("_id") on update cascade on delete cascade,"
        + "FRIENDS text not null,USERNAME text ,NUMBERINPUT text,SCORE text);";

当你插入

public void insertFriend(long playerId, String Friend) {
    ContentValues initialValues = new ContentValues();
    initialValues.put("player_id", playerId);
    initialValues.put("FRIENDS", Friend);
    db.insertWithOnConflict("FRIENDSLIST", null, initialValues, SQLiteDatabase.CONFLICT_IGNORE);
}

结交朋友

public Cursor getFriend(long rowid) throws SQLException {
    Cursor mCursor = db.query(true, "FRIENDSLIST", new String[] {
            "_id", "FRIENDS"
    }, player_id + " =  " + "rowid", null, null, null, null, null);
    // cursor from query is never null, 
    // should just check for if (cursor.moveToFirst()) in the calling activity
    return mCursor;
}

在数据库中打开方法添加

public DBAdapter open() throws SQLiteException {
    db = DBHelper.getWritableDatabase();
    db.execSQL("PRAGMA foreign_keys=ON;"); 
    return this;
}
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