/* * Copyright (C) 2007 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.database.sqlite; import android.content.Context; import android.database.DatabaseErrorHandler; import android.database.DefaultDatabaseErrorHandler; import android.database.sqlite.SQLiteDatabase.CursorFactory; import android.util.Log; /** * A helper class to manage database creation and version management. * *

You create a subclass implementing {@link #onCreate}, {@link #onUpgrade} and * optionally {@link #onOpen}, and this class takes care of opening the database * if it exists, creating it if it does not, and upgrading it as necessary. * Transactions are used to make sure the database is always in a sensible state. * *

This class makes it easy for {@link android.content.ContentProvider} * implementations to defer opening and upgrading the database until first use, * to avoid blocking application startup with long-running database upgrades. * *

For an example, see the NotePadProvider class in the NotePad sample application, * in the samples/ directory of the SDK.

* *

Note: this class assumes * monotonically increasing version numbers for upgrades.

*/ public abstract class SQLiteOpenHelper { private static final String TAG = SQLiteOpenHelper.class.getSimpleName(); private final Context mContext; private final String mName; private final CursorFactory mFactory; private final int mNewVersion; private SQLiteDatabase mDatabase = null; private boolean mIsInitializing = false; private final DatabaseErrorHandler mErrorHandler; /** * Create a helper object to create, open, and/or manage a database. * This method always returns very quickly. The database is not actually * created or opened until one of {@link #getWritableDatabase} or * {@link #getReadableDatabase} is called. * * @param context to use to open or create the database * @param name of the database file, or null for an in-memory database * @param factory to use for creating cursor objects, or null for the default * @param version number of the database (starting at 1); if the database is older, * {@link #onUpgrade} will be used to upgrade the database; if the database is * newer, {@link #onDowngrade} will be used to downgrade the database */ public SQLiteOpenHelper(Context context, String name, CursorFactory factory, int version) { this(context, name, factory, version, new DefaultDatabaseErrorHandler()); } /** * Create a helper object to create, open, and/or manage a database. * The database is not actually created or opened until one of * {@link #getWritableDatabase} or {@link #getReadableDatabase} is called. * *

Accepts input param: a concrete instance of {@link DatabaseErrorHandler} to be * used to handle corruption when sqlite reports database corruption.

* * @param context to use to open or create the database * @param name of the database file, or null for an in-memory database * @param factory to use for creating cursor objects, or null for the default * @param version number of the database (starting at 1); if the database is older, * {@link #onUpgrade} will be used to upgrade the database * @param errorHandler the {@link DatabaseErrorHandler} to be used when sqlite reports database * corruption. */ public SQLiteOpenHelper(Context context, String name, CursorFactory factory, int version, DatabaseErrorHandler errorHandler) { if (version < 1) throw new IllegalArgumentException("Version must be >= 1, was " + version); if (errorHandler == null) { throw new IllegalArgumentException("DatabaseErrorHandler param value can't be null."); } mContext = context; mName = name; mFactory = factory; mNewVersion = version; mErrorHandler = errorHandler; } /** * Return the name of the SQLite database being opened, as given tp * the constructor. */ public String getDatabaseName() { return mName; } /** * Create and/or open a database that will be used for reading and writing. * The first time this is called, the database will be opened and * {@link #onCreate}, {@link #onUpgrade} and/or {@link #onOpen} will be * called. * *

Once opened successfully, the database is cached, so you can * call this method every time you need to write to the database. * (Make sure to call {@link #close} when you no longer need the database.) * Errors such as bad permissions or a full disk may cause this method * to fail, but future attempts may succeed if the problem is fixed.

* *

Database upgrade may take a long time, you * should not call this method from the application main thread, including * from {@link android.content.ContentProvider#onCreate ContentProvider.onCreate()}. * * @throws SQLiteException if the database cannot be opened for writing * @return a read/write database object valid until {@link #close} is called */ public synchronized SQLiteDatabase getWritableDatabase() { if (mDatabase != null) { if (!mDatabase.isOpen()) { // darn! the user closed the database by calling mDatabase.close() mDatabase = null; } else if (!mDatabase.isReadOnly()) { return mDatabase; // The database is already open for business } } if (mIsInitializing) { throw new IllegalStateException("getWritableDatabase called recursively"); } // If we have a read-only database open, someone could be using it // (though they shouldn't), which would cause a lock to be held on // the file, and our attempts to open the database read-write would // fail waiting for the file lock. To prevent that, we acquire the // lock on the read-only database, which shuts out other users. boolean success = false; SQLiteDatabase db = null; if (mDatabase != null) mDatabase.lock(); try { mIsInitializing = true; if (mName == null) { db = SQLiteDatabase.create(null); } else { db = mContext.openOrCreateDatabase(mName, 0, mFactory, mErrorHandler); } int version = db.getVersion(); if (version != mNewVersion) { db.beginTransaction(); try { if (version == 0) { onCreate(db); } else { if (version > mNewVersion) { onDowngrade(db, version, mNewVersion); } else { onUpgrade(db, version, mNewVersion); } } db.setVersion(mNewVersion); db.setTransactionSuccessful(); } finally { db.endTransaction(); } } onOpen(db); success = true; return db; } finally { mIsInitializing = false; if (success) { if (mDatabase != null) { try { mDatabase.close(); } catch (Exception e) { } mDatabase.unlock(); } mDatabase = db; } else { if (mDatabase != null) mDatabase.unlock(); if (db != null) db.close(); } } } /** * Create and/or open a database. This will be the same object returned by * {@link #getWritableDatabase} unless some problem, such as a full disk, * requires the database to be opened read-only. In that case, a read-only * database object will be returned. If the problem is fixed, a future call * to {@link #getWritableDatabase} may succeed, in which case the read-only * database object will be closed and the read/write object will be returned * in the future. * *

Like {@link #getWritableDatabase}, this method may * take a long time to return, so you should not call it from the * application main thread, including from * {@link android.content.ContentProvider#onCreate ContentProvider.onCreate()}. * * @throws SQLiteException if the database cannot be opened * @return a database object valid until {@link #getWritableDatabase} * or {@link #close} is called. */ public synchronized SQLiteDatabase getReadableDatabase() { if (mDatabase != null) { if (!mDatabase.isOpen()) { // darn! the user closed the database by calling mDatabase.close() mDatabase = null; } else { return mDatabase; // The database is already open for business } } if (mIsInitializing) { throw new IllegalStateException("getReadableDatabase called recursively"); } try { return getWritableDatabase(); } catch (SQLiteException e) { if (mName == null) throw e; // Can't open a temp database read-only! Log.e(TAG, "Couldn't open " + mName + " for writing (will try read-only):", e); } SQLiteDatabase db = null; try { mIsInitializing = true; String path = mContext.getDatabasePath(mName).getPath(); db = SQLiteDatabase.openDatabase(path, mFactory, SQLiteDatabase.OPEN_READONLY, mErrorHandler); if (db.getVersion() != mNewVersion) { throw new SQLiteException("Can't upgrade read-only database from version " + db.getVersion() + " to " + mNewVersion + ": " + path); } onOpen(db); Log.w(TAG, "Opened " + mName + " in read-only mode"); mDatabase = db; return mDatabase; } finally { mIsInitializing = false; if (db != null && db != mDatabase) db.close(); } } /** * Close any open database object. */ public synchronized void close() { if (mIsInitializing) throw new IllegalStateException("Closed during initialization"); if (mDatabase != null && mDatabase.isOpen()) { mDatabase.close(); mDatabase = null; } } /** * Called when the database is created for the first time. This is where the * creation of tables and the initial population of the tables should happen. * * @param db The database. */ public abstract void onCreate(SQLiteDatabase db); /** * Called when the database needs to be upgraded. The implementation * should use this method to drop tables, add tables, or do anything else it * needs to upgrade to the new schema version. * *

The SQLite ALTER TABLE documentation can be found * here. If you add new columns * you can use ALTER TABLE to insert them into a live table. If you rename or remove columns * you can use ALTER TABLE to rename the old table, then create the new table and then * populate the new table with the contents of the old table. * * @param db The database. * @param oldVersion The old database version. * @param newVersion The new database version. */ public abstract void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion); /** * Called when the database needs to be downgraded. This is stricly similar to * onUpgrade() method, but is called whenever current version is newer than requested one. * However, this method is not abstract, so it is not mandatory for a customer to * implement it. If not overridden, default implementation will reject downgrade and * throws SQLiteException * * @param db The database. * @param oldVersion The old database version. * @param newVersion The new database version. */ public void onDowngrade(SQLiteDatabase db, int oldVersion, int newVersion) { throw new SQLiteException("Can't downgrade database from version " + oldVersion + " to " + newVersion); } /** * Called when the database has been opened. The implementation * should check {@link SQLiteDatabase#isReadOnly} before updating the * database. * * @param db The database. */ public void onOpen(SQLiteDatabase db) {} }