未创建 Android SQLite 表

Question

我正在尝试创建一个统计表，但由于某种原因，直到我第一次调用 StatisticsAdapter.insertEntry() 时它才会创建。之后，我可以删除该代码，重新加载新版本，然后一切正常。由于这在现实生活中行不通，我想知道如何创建一个空表？

目前if(StatisticsAdapter.getCount(isbn) < 1) 有一个错误，因为它说没有这样的表。为什么会这样？

主代码

StatisticsAdapter=new StatisticsAdapter(this);
    StatisticsAdapter=StatisticsAdapter.open();
    Calendar curDate = Calendar.getInstance();
    if(StatisticsAdapter.getCount(isbn) < 1)
        StatisticsAdapter.insertEntry(isbn, curDate.get(Calendar.YEAR), (curDate.get(Calendar.MONTH)+1), 1);
    else
        StatisticsAdapter.increaseCount(isbn);

StatisticsAdapter

public class StatisticsAdapter {
public static final int NAME_COLUMN = 1;
static final String tableName="STATISTICS";
// TODO: Create public field for each column in your table.
// SQL Statement to create a new database.
public static final String STATISTICS_TABLE_CREATE = "create table "+"STATISTICS"
        + "( " +"ID"+" integer primary key autoincrement,"
        + "ISBN text,"
        + "YEAR text,"
        + "MONTH text,"
        + "COUNT integer); ";
// Variable to hold the database instance
public  SQLiteDatabase db;
// Context of the application using the database.
private final Context context;
// Database open/upgrade helper
private DataBaseHelper dbHelper;
public  StatisticsAdapter(Context _context) 
{
    context = _context;
    dbHelper = new DataBaseHelper(context);
}
public  StatisticsAdapter open() throws SQLException 
{
    db = dbHelper.getWritableDatabase();
    return this;
}
public void close() 
{
    db.close();
}

public  SQLiteDatabase getDatabaseInstance()
{
    return db;
}

public void insertEntry(String ISBN, int year, int month, int count)
{
   ContentValues newValues = new ContentValues();
    // Assign values for each row.
    newValues.put("ISBN", ISBN);
    newValues.put("YEAR", ((Integer)year).toString());
    if(month>=10)
        newValues.put("MONTH", ((Integer)month).toString());
    else
        newValues.put("MONTH", "0"+((Integer)month).toString());
    newValues.put("COUNT", count);

    // Insert the row into your table
    db.insert("STATISTICS", null, newValues);
    ///Toast.makeText(context, "Reminder Is Successfully Saved", Toast.LENGTH_LONG).show();
}
public int getCount(String ISBN)
    {
        //Query
        String query = "select COUNT from STATISTICS where ISBN = ?";
        Cursor cursor = db.rawQuery(query, new String[] {ISBN});
        if(cursor.getCount()<1) // title Not Exist
        {
            cursor.close();
            return 0;
        }
        cursor.moveToFirst();
        int count = cursor.getInt(cursor.getColumnIndex("COUNT"));
        cursor.close();
        return count;               
    }

DataBaseHelper

public class DataBaseHelper extends SQLiteOpenHelper
{   
    // Database Version
        private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "database.db";

    // ============================ End Variables ===========================

    public DataBaseHelper(Context context, String name, CursorFactory factory, int version) 
    {
               super(context, name, factory, version);
    }

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

    // Called when no database exists in disk and the helper class needs
    // to create a new one.
    @Override
    public void onCreate(SQLiteDatabase _db) 
    {
            _db.execSQL(LoginDataBaseAdapter.USER_TABLE_CREATE);
            _db.execSQL(CheckOutDataBaseAdapter.CHECKOUT_TABLE_CREATE);
            _db.execSQL(InventoryAdapter.INVENTORY_TABLE_CREATE);
            _db.execSQL(StatisticsAdapter.STATISTICS_TABLE_CREATE);
    }
    // Called when there is a database version mismatch meaning that the version
    // of the database on disk needs to be upgraded to the current version.
    @Override
    public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion) 
    {
            // Log the version upgrade.
            Log.w("TaskDBAdapter", "Upgrading from version " +_oldVersion + " to " +_newVersion + ", which will destroy all old data");


            // Upgrade the existing database to conform to the new version. Multiple
            // previous versions can be handled by comparing _oldVersion and _newVersion
            // values.
            // on upgrade drop older tables
            _db.execSQL("DROP TABLE IF EXISTS " + LoginDataBaseAdapter.USER_TABLE_CREATE);
            _db.execSQL("DROP TABLE IF EXISTS " + CheckOutDataBaseAdapter.CHECKOUT_TABLE_CREATE);
            _db.execSQL("DROP TABLE IF EXISTS " + InventoryAdapter.INVENTORY_TABLE_CREATE);
            _db.execSQL("DROP TABLE IF EXISTS " + StatisticsAdapter.STATISTICS_TABLE_CREATE);

            // Create a new one.
            onCreate(_db);
    }

}

Answer 1

尝试扩展SQLiteOpenHelper

覆盖

@Override
  public void onCreate(SQLiteDatabase database) {
    database.execSQL(DATABASE_CREATE);
  }

在调用getWritableDatabase() 或getReadableDatabase() 之一之前，不会实际创建或打开数据库。

Answer 2

您是否尝试过在运行代码之前卸载应用程序？如果您之前的代码版本创建的 db 没有统计表，您必须增加数据库版本 (DatabaseHelper.DATABASE_VERSION) 以触发 onUpgrade 调用，这将创建表。

您可以尝试的第二件事是将表名提取为常量并使用它来代替硬编码字符串。也许你在某个地方有错字？

我还建议从设备中提取数据库并使用命令行 sqlite 客户端检查其架构：

adb shell
busybox cp data/data/com.your.package/databases/database.db /sdcard
exit
adb pull /sdcard/database.db
sqlite3 database.db
.schema

Answer 3

创建类DatabaseHandler extends SQLiteOpenHelper

并像下面这样覆盖：

// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_CONTACTS_TABLE = Crate table query;
    db.execSQL(CREATE_CONTACTS_TABLE);
}

现在，您想从您的Activity 调用SQLiteDatabase db = cintext.getWritableDatabase(); 来访问数据库表。

Answer 4

当设备上的应用程序版本较低并且您更改数据库（添加表，创建新数据库，...）并安装新版本时，会发生此问题，现在应用程序尝试创建新数据库但不能在数据库上创建和更改修改。

解决办法是：

只需更改DATABASE_VERSION

应用强制创建新数据库

祝你好运

Answer 5

只需更新 dbHelper 类中的 DATABASE_VERSION。