[英]Check if database exists in sqlite
我有一个带有sqllite数据库的android应用。 该数据库具有各种表。 到目前为止,我有两个表,但发生错误:首先创建表A时,运行表B的代码时,我的应用程序崩溃; 当我先创建表B然后再创建表A时,应用程序也崩溃了。 我必须清除我的应用程序缓存,这样我才能“更改”访问权限,因此我永远无法在同一应用程序“运行”中访问这两个地址。 我认为是因为我在添加新表时会重新创建数据库。 为了避免这种情况,我尝试检查数据库是否已经存在,如果不存在,则不重新创建,但是我在构造函数中进行了检查,而android不允许。
日志:
12-25 00:30:28.024 32031-32031 / com.support.android.iplfit E / AndroidRuntime:致命例外:主进程:com.support.android.iplfit,PID:32031 android.database.sqlite.SQLiteException:无此类表:Dica(代码1):,编译时:从Dica在android.database.sqlite.SQLite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889)在android.database.sqlite.SQLite.SQLiteConnection.nativePrepareStatement(本机方法)在android.database .sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500)在android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)在android.database.sqlite.SQLiteProgram。(SQLiteProgram.java:58)在android.database .sqlite.SQLiteStatement。(SQLiteStatement.java:31)位于android.database.sqlite.SQLiteDatabase.delete(SQLiteDatabase.java:1499)位于com.support.android.iplfit.BDHelpers.DicaBDHelper.removerAllDicasBD(DicaBDHelper.java:73) com.support.and上的com.support.android.iplfit.Singletons.SingletonDicas.adicionarDicasBD(SingletonDicas.java:65) roid.roid.iplfit.Singletons.SingletonDicas $ 1.onResponse(SingletonDicas.java:83)位于com.support.android.iplfit.Singletons.SingletonDicas $ 1.onResponse(SingletonDicas.java:77),位于com.Junior.volley.toolbox.com。 com.android.volley.ExecutorDelivery $ ResponseDeliveryRunnable.run(ExecutorDelivery.java:99)的android.os.Handler.handleCallback(Handler.java:751)的android.os.Handler.dispatchMessage的deliveryResponse(JsonRequest.java:65) (Handler.java:95)在android.os.Looper.loop(Looper.java:154)在android.app.ActivityThread.main(ActivityThread.java:6077)在java.lang.reflect.Method.invoke(本机方法)在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:866)在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
我创建一张表的类之一:
public class DicaBDHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "db_iplfit";
private static final int DB_VERSION = 1;
private static final String TABLE_NAME = "Dica";
private static final String ID_DICA = "id";
private static final String CHANNEL_DICA = "channel";
private static final String TITULO_DICA = "titulo";
private static final String CONTEUDO_DICA = "conteudo";
private final SQLiteDatabase database;
public DicaBDHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
this.database = getWritableDatabase();
}
private static boolean haveDB(Context context, String dbName) {
File dbFile = context.getDatabasePath(dbName);
return dbFile.exists();
}
@Override
public void onCreate(SQLiteDatabase database) {
String createDicaTable = "CREATE TABLE " + TABLE_NAME + "( " +
ID_DICA + " INTEGER UNSIGNED PRIMARY KEY," +
CHANNEL_DICA + " TEXT NOT NULL," +
TITULO_DICA + " TEXT NOT NULL," +
CONTEUDO_DICA + " TEXT NOT NULL" + ")";
database.execSQL(createDicaTable);
}
@Override
public void onUpgrade(SQLiteDatabase database, int i, int j) {
String sql = "DROP TABLE IF EXISTS " + TABLE_NAME;
database.execSQL(sql);
//this.onCreate(database);
}
}
使用onCreate
创建多个表:
@Override
public void onCreate(SQLiteDatabase database) {
String createDicaTable = "CREATE TABLE " + TABLE_NAME + "( " +
ID_DICA + " INTEGER UNSIGNED PRIMARY KEY," +
CHANNEL_DICA + " TEXT NOT NULL," +
TITULO_DICA + " TEXT NOT NULL," +
CONTEUDO_DICA + " TEXT NOT NULL" + ")";
database.execSQL(createDicaTable);
// Next table
String createanothertable = "CREATE TABLE anothertable (column TEXT)";
database.execSQK(createanothertable);
// etc
}
注意! 仅当数据库不存在时, onCreate
才会自动运行
创建后续(缺失)表(假定与其他表具有独立性),而不必删除现有表。
根据需要运行或每次运行App时运行(因此代码IF NOT EXISTS
)。
public void addMissingTables() {
String createanothertable = "CREATE TABLE IF NOT EXISTS anothertable (column TEXT)";
database.execSQL(createanothertable);
// etc
}
注意! 假定方法已添加到Databasehelper(so db)
注意! 获取DatabaseHelper实例后应该不会有问题,因为this.database = getWritableDatabase();
如果数据库不存在,将强制DatabaseHelper创建数据库。
您还可以在onCreate
为表编写“ IF NOT EXISTS
代码,并以类似的方式调用它。
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
checkDB = SQLiteDatabase.openDatabase(DB_FULL_PATH(DB_FULL_PATH is the path to your database file), null,
SQLiteDatabase.OPEN_READONLY);
checkDB.close();
} catch (SQLiteException e) {
// database doesn't exist yet.
}
return checkDB != null;
}
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