Android
SQLite

Wprowadzenie

Uwagi

Korzystanie z klasy SQLiteOpenHelper

public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "Example.db";
    private static final int DATABASE_VERSION = 3;

    // For all Primary Keys _id should be used as column name
    public static final String COLUMN_ID = "_id";

    // Definition of table and column names of Products table
    public static final String TABLE_PRODUCTS = "Products";
    public static final String COLUMN_NAME = "Name";
    public static final String COLUMN_DESCRIPTION = "Description";
    public static final String COLUMN_VALUE = "Value";

    // Definition of table and column names of Transactions table
    public static final String TABLE_TRANSACTIONS = "Transactions";
    public static final String COLUMN_PRODUCT_ID = "ProductId";
    public static final String COLUMN_AMOUNT = "Amount";

    // Create Statement for Products Table
    private static final String CREATE_TABLE_PRODUCT = "CREATE TABLE " + TABLE_PRODUCTS + "  (" +
            COLUMN_ID + " INTEGER PRIMARY KEY, " +
            COLUMN_DESCRIPTION + " TEXT, " +
            COLUMN_NAME + " TEXT, " +
            COLUMN_VALUE + " REAL" +
            ");";

    // Create Statement for Transactions Table
    private static final String CREATE_TABLE_TRANSACTION = "CREATE TABLE " + TABLE_TRANSACTIONS + "  (" +
            COLUMN_ID + " INTEGER PRIMARY KEY," +
            COLUMN_PRODUCT_ID + " INTEGER," +
            COLUMN_AMOUNT + " INTEGER," +
            " FOREIGN KEY (" + COLUMN_PRODUCT_ID + ") REFERENCES " + TABLE_PRODUCTS + "(" + COLUMN_ID + ")" +
            ");";

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        // onCreate should always create your most up to date database
        // This method is called when the app is newly installed
        db.execSQL(CREATE_TABLE_PRODUCT);
        db.execSQL(CREATE_TABLE_TRANSACTION);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // onUpgrade is responsible for upgrading the database when you make
        // changes to the schema. For each version the specific changes you made
        // in that version have to be applied.
        for (int version = oldVersion + 1; version <= newVersion; version++) {
            switch (version) {

                case 2:
                    db.execSQL("ALTER TABLE " + TABLE_PRODUCTS + " ADD COLUMN " + COLUMN_DESCRIPTION + " TEXT;");
                    break;

                case 3:
                    db.execSQL(CREATE_TABLE_TRANSACTION);
                    break;
            }
        }
    }
}

Wstaw dane do bazy danych

// You need a writable database to insert data
final SQLiteDatabase database = openHelper.getWritableDatabase();

// Create a ContentValues instance which contains the data for each column
// You do not need to specify a value for the PRIMARY KEY column.
// Unique values for these are automatically generated.
final ContentValues values = new ContentValues();
values.put(COLUMN_NAME, model.getName());
values.put(COLUMN_DESCRIPTION, model.getDescription());
values.put(COLUMN_VALUE, model.getValue());

// This call performs the update
// The return value is the rowId or primary key value for the new row!
// If this method returns -1 then the insert has failed.
final int id = database.insert(
        TABLE_NAME, // The table name in which the data will be inserted
        null,       // String: optional; may be null. If your provided values is empty,
                    // no column names are known and an empty row can't be inserted.
                    // If not set to null, this parameter provides the name
                    // of nullable column name to explicitly insert a NULL

        values      // The ContentValues instance which contains the data
);

Metoda onUpgrade ()

SQLiteOpenHelper to klasa pomocnicza do zarządzania tworzeniem baz danych i zarządzaniem wersjami.

W tej klasie metoda onUpgrade() odpowiada za aktualizację bazy danych podczas wprowadzania zmian w schemacie. Jest wywoływany, gdy plik bazy danych już istnieje, ale jego wersja jest niższa niż wersja określona w bieżącej wersji aplikacji. W przypadku każdej wersji bazy danych należy wprowadzić określone zmiany.

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Loop through each version when an upgrade occurs.
    for (int version = oldVersion + 1; version <= newVersion; version++) {
        switch (version) {

            case 2:
                // Apply changes made in version 2
                db.execSQL(
                    "ALTER TABLE " +
                    TABLE_PRODUCTS +
                    " ADD COLUMN " +
                    COLUMN_DESCRIPTION +
                    " TEXT;"
                );
                break;

            case 3:
                // Apply changes made in version 3
                db.execSQL(CREATE_TABLE_TRANSACTION);
                break;
        }
    }
}

Odczytywanie danych z kursora

Oto przykład metody, która SQLiteOpenHelper podklasie SQLiteOpenHelper . Używa ciągu searchTerm do filtrowania wyników, iteruje zawartość Kursora i zwraca tę zawartość na List obiektów Product .

Najpierw zdefiniuj klasę POJO Product która będzie kontenerem dla każdego wiersza pobranego z bazy danych:

public class Product {
  long mId;
  String mName;
  String mDescription;
  float mValue;
  public Product(long id, String name, String description, float value) {
    mId = id;
    mName = name;
    mDescription = description;
    mValue = value;
  }
}

Następnie zdefiniuj metodę, która będzie przeszukiwać bazę danych i zwróci List obiektów Product :

public List<Product> searchForProducts(String searchTerm) {
    
    // When reading data one should always just get a readable database.
    final SQLiteDatabase database = this.getReadableDatabase();

    final Cursor cursor = database.query(
            // Name of the table to read from
            TABLE_NAME,

            // String array of the columns which are supposed to be read
            new String[]{COLUMN_NAME, COLUMN_DESCRIPTION, COLUMN_VALUE},

            // The selection argument which specifies which row is read.
            // ? symbols are parameters.
            COLUMN_NAME + " LIKE ?",

            // The actual parameters values for the selection as a String array.
            // ? above take the value from here
            new String[]{"%" + searchTerm + "%"},

            // GroupBy clause. Specify a column name to group similar values
            // in that column together.
            null,

            // Having clause. When using the GroupBy clause this allows you to
            // specify which groups to include.
            null,

            // OrderBy clause. Specify a column name here to order the results
            // according to that column. Optionally append ASC or DESC to specify
            // an ascending or descending order.
            null
    );

    // To increase performance first get the index of each column in the cursor
    final int idIndex = cursor.getColumnIndex(COLUMN_ID);
    final int nameIndex = cursor.getColumnIndex(COLUMN_NAME);
    final int descriptionIndex = cursor.getColumnIndex(COLUMN_DESCRIPTION);
    final int valueIndex = cursor.getColumnIndex(COLUMN_VALUE);

    try {

        // If moveToFirst() returns false then cursor is empty
        if (!cursor.moveToFirst()) {
            return new ArrayList<>();
        }

        final List<Product> products = new ArrayList<>();

        do {

            // Read the values of a row in the table using the indexes acquired above
            final long id = cursor.getLong(idIndex);
            final String name = cursor.getString(nameIndex);
            final String description = cursor.getString(descriptionIndex);
            final float value = cursor.getFloat(valueIndex);

            products.add(new Product(id, name, description, value));

        } while (cursor.moveToNext());

        return products;

    } finally {
        // Don't forget to close the Cursor once you are done to avoid memory leaks.
        // Using a try/finally like in this example is usually the best way to handle this
        cursor.close();

        // close the database
        database.close();
    }
}

Utwórz umowę, pomocnika i dostawcę SQLite w systemie Android

DBContract.java

//Define the tables and columns of your local database
public final class DBContract {
/*Content Authority its a name for the content provider, is convenient to use the package app name to be unique on the device */
            
    public static final String CONTENT_AUTHORITY = "com.yourdomain.yourapp";
            
    //Use CONTENT_AUTHORITY to create all the database URI's that the app will use to link the content provider.
    public static final Uri BASE_CONTENT_URI = Uri.parse("content://" + CONTENT_AUTHORITY);
        
    /*the name of the uri that can be the same as the name of your table. 
    this will translate to content://com.yourdomain.yourapp/user/ as a valid URI
    */
    public static final String PATH_USER = "User";

    // To prevent someone from accidentally instantiating the contract class,
    // give it an empty constructor.
    public DBContract () {}
    
    //Intern class that defines the user table
    public static final class UserEntry implements BaseColumns {
        public static final URI CONTENT_URI = BASE_CONTENT_URI.buildUpon().appendPath(PATH_USER).build();
        
        public static final String CONTENT_TYPE = ContentResolver.CURSOR_DIR_BASE_TYPE+"/"+CONTENT_AUTHORITY+"/"+PATH_USER;
        
        //Name of the table
        public static final String TABLE_NAME="User";
        
        //Columns of the user table
        public static final String COLUMN_Name="Name";
        public static final String COLUMN_Password="Password";
        
        public static Uri buildUri(long id){
            return ContentUris.withAppendedId(CONTENT_URI,id);
        }
}

DBHelper.java

public class DBHelper extends SQLiteOpenHelper{

//if you change the schema of the database, you must increment this number
private static final int DATABASE_VERSION=1;
static final String DATABASE_NAME="mydatabase.db";
private static DBHelper mInstance=null;
public static DBHelper getInstance(Context ctx){
    if(mInstance==null){
    mInstance= new DBHelper(ctx.getApplicationContext());
    }
    return mInstance;
}

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

public int GetDatabase_Version() {
    return DATABASE_VERSION;
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase){
//Create the table users
final String SQL_CREATE_TABLE_USERS="CREATE TABLE "+UserEntry.TABLE_NAME+ " ("+
UserEntry._ID+" INTEGER PRIMARY KEY, "+
UserEntry.COLUMN_Name+" TEXT , "+
UserEntry.COLUMN_Password+" TEXT "+
" ); ";

sqLiteDatabase.execSQL(SQL_CREATE_TABLE_USERS);

}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + UserEntry.TABLE_NAME);
}

}

DBProvider.java

public class DBProvider extends ContentProvider {

    private static final UriMatcher sUriMatcher = buildUriMatcher();
    private DBHelper mDBHelper;
    private Context mContext;

    static final int USER = 100;

    static UriMatcher buildUriMatcher() {

        final UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
        final String authority = DBContract.CONTENT_AUTHORITY;

        matcher.addURI(authority, DBContract.PATH_USER, USER);

        return matcher;
    }

    @Override
    public boolean onCreate() {
        mDBHelper = new DBHelper(getContext());
        return false;
    }

    public PeaberryProvider(Context context) {
        mDBHelper = DBHelper.getInstance(context);
        mContext = context;
    }

    @Override
    public String getType(Uri uri) {
        // determine what type of Uri is
        final int match = sUriMatcher.match(uri);

        switch (match) {
            case USER:
                return DBContract.UserEntry.CONTENT_TYPE;
            
            default:
                throw new UnsupportedOperationException("Uri unknown: " + uri);
        }
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
                        String sortOrder) {
        Cursor retCursor;
        try {
            switch (sUriMatcher.match(uri)) {
                case USER: {
                    retCursor = mDBHelper.getReadableDatabase().query(
                            DBContract.UserEntry.TABLE_NAME,
                            projection,
                            selection,
                            selectionArgs,
                            null,
                            null,
                            sortOrder
                    );
                    break;
                }
                default:
                    throw new UnsupportedOperationException("Uri unknown: " + uri);
            }
        } catch (Exception ex) {
            Log.e("Cursor", ex.toString());
        } finally {
            mDBHelper.close();
        }
        return null;
    }

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        final SQLiteDatabase db = mDBHelper.getWritableDatabase();
        final int match = sUriMatcher.match(uri);
        Uri returnUri;
        try {

            switch (match) {
                case USER: {
                    long _id = db.insert(DBContract.UserEntry.TABLE_NAME, null, values);
                    if (_id > 0)
                        returnUri = DBContract.UserEntry.buildUri(_id);
                    else
                        throw new android.database.SQLException("Error at inserting row in " + uri);
                    break;
                }
                default:
                    throw new UnsupportedOperationException("Uri unknown: " + uri);
            }
            mContext.getContentResolver().notifyChange(uri, null);
            return returnUri;
        } catch (Exception ex) {
            Log.e("Insert", ex.toString());
            db.close();
        } finally {
            db.close();
        }
        return null;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        final SQLiteDatabase db = DBHelper.getWritableDatabase();
        final int match = sUriMatcher.match(uri);
        int deletedRows;
        if (null == selection) selection = "1";
        try {
            switch (match) {
                case USER:
                    deletedRows = db.delete(
                            DBContract.UserEntry.TABLE_NAME, selection, selectionArgs);
                    break;
                default:
                    throw new UnsupportedOperationException("Uri unknown: " + uri);
            }
            if (deletedRows != 0) {
                mContext.getContentResolver().notifyChange(uri, null);
            }
            return deletedRows;
        } catch (Exception ex) {
            Log.e("Insert", ex.toString());
        } finally {
            db.close();
        }
        return 0;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        final SQLiteDatabase db = mDBHelper.getWritableDatabase();
        final int match = sUriMatcher.match(uri);
        int updatedRows;
        try {
            switch (match) {
                case USER:
                    updatedRows = db.update(DBContract.UserEntry.TABLE_NAME, values, selection, selectionArgs);
                    break;
                default:
                    throw new UnsupportedOperationException("Uri unknown: " + uri);
            }
            if (updatedRows != 0) {
                mContext.getContentResolver().notifyChange(uri, null);
            }
            return updatedRows;
        } catch (Exception ex) {
            Log.e("Update", ex.toString());
        } finally {
            db.close();
        }
        return -1;
    }

}

Jak używać:

public void InsertUser() {
    try {
        ContentValues userValues = getUserData("Jhon","XXXXX");
        DBProvider dbProvider = new DBProvider(mContext);
        dbProvider.insert(UserEntry.CONTENT_URI, userValues);

    } catch (Exception ex) {
        Log.e("Insert", ex.toString());
    }
}

public ContentValues getUserData(String name, String pass) {
    ContentValues userValues = new ContentValues();
    userValues.put(UserEntry.COLUMN_Name, name);
    userValues.put(UserEntry.COLUMN_Password, pass);
    return userValues;
}

Aktualizowanie wiersza w tabeli

// You need a writable database to update a row
final SQLiteDatabase database = openHelper.getWritableDatabase();

// Create a ContentValues instance which contains the up to date data for each column
// Unlike when inserting data you need to specify the value for the PRIMARY KEY column as well
final ContentValues values = new ContentValues();
values.put(COLUMN_ID, model.getId());
values.put(COLUMN_NAME, model.getName());
values.put(COLUMN_DESCRIPTION, model.getDescription());
values.put(COLUMN_VALUE, model.getValue());

// This call performs the update
// The return value tells you how many rows have been updated.
final int count = database.update(
        TABLE_NAME,         // The table name in which the data will be updated
        values,             // The ContentValues instance with the new data
        COLUMN_ID + " = ?", // The selection which specifies which row is updated. ? symbols are parameters.
        new String[] {      // The actual parameters for the selection as a String[]. 
                String.valueOf(model.getId()) 
        }  
);

Przeprowadzanie transakcji

Transakcji można użyć do atomowego wprowadzenia wielu zmian w bazie danych. Każda normalna transakcja odbywa się według tego wzoru:

// You need a writable database to perform transactions
final SQLiteDatabase database = openHelper.getWritableDatabase();

// This call starts a transaction
database.beginTransaction();

// Using try/finally is essential to reliably end transactions even 
// if exceptions or other problems occur.
try {

    // Here you can make modifications to the database
    database.insert(TABLE_CARS, null, productValues);
    database.update(TABLE_BUILDINGS, buildingValues, COLUMN_ID + " = ?", new String[] { String.valueOf(buildingId) });
    
    // This call marks a transaction as successful. 
    // This causes the changes to be written to the database once the transaction ends.  
    database.setTransactionSuccessful();
} finally {
    // This call ends a transaction.
    // If setTransactionSuccessful() has not been called then all changes 
    // will be rolled back and the database will not be modified.
    database.endTransaction();
}

Wywołanie funkcji beginTransaction() wewnątrz aktywnych transakcji nie ma wpływu.

Usuń wiersze z tabeli

Aby usunąć wszystkie wiersze z tabeli

//get writable database
SQLiteDatabase db = openHelper.getWritableDatabase();

db.delete(TABLE_NAME, null, null);
db.close();

Aby usunąć wszystkie wiersze z tabeli i uzyskać liczbę usuniętych wierszy w wartości zwracanej

//get writable database
SQLiteDatabase db = openHelper.getWritableDatabase();

int numRowsDeleted = db.delete(TABLE_NAME, String.valueOf(1), null);
db.close();

Aby usunąć wiersze z warunkiem WHERE

//get writable database
SQLiteDatabase db = openHelper.getWritableDatabase();

String whereClause = KEY_NAME + " = ?";
String[] whereArgs = new String[]{String.valueOf(KEY_VALUE)};

//for multiple condition, join them with AND
//String whereClause = KEY_NAME1 + " = ? AND " + KEY_NAME2 + " = ?";
//String[] whereArgs = new String[]{String.valueOf(KEY_VALUE1), String.valueOf(KEY_VALUE2)};

int numRowsDeleted = db.delete(TABLE_NAME, whereClause, whereArgs);
db.close();

Przechowuj obraz w SQLite

Konfigurowanie bazy danych

public class DatabaseHelper extends SQLiteOpenHelper {
    // Database Version
    private static final int DATABASE_VERSION = 1;
 
    // Database Name
    private static final String DATABASE_NAME = "database_name";
 
    // Table Names
    private static final String DB_TABLE = "table_image";
    
    // column names
    private static final String KEY_NAME = "image_name";
    private static final String KEY_IMAGE = "image_data";
    
    // Table create statement
    private static final String CREATE_TABLE_IMAGE = "CREATE TABLE " + DB_TABLE + "("+ 
                       KEY_NAME + " TEXT," + 
                       KEY_IMAGE + " BLOB);";

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
 
    @Override
    public void onCreate(SQLiteDatabase db) {
 
        // creating table
        db.execSQL(CREATE_TABLE_IMAGE);
    }
 
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // on upgrade drop older tables
        db.execSQL("DROP TABLE IF EXISTS " + DB_TABLE);

        // create new table
        onCreate(db);
    }
}

Wstaw do bazy danych:

public void addEntry( String name, byte[] image) throws SQLiteException{
    SQLiteDatabase database = this.getWritableDatabase();
    ContentValues cv = new  ContentValues();
    cv.put(KEY_NAME,     name);
    cv.put(KEY_IMAGE,     image);
    database.insert( DB_TABLE, null, cv );
}

Pobieranie danych :

 byte[] image = cursor.getBlob(1);

Uwaga:

1. Przed wstawieniem do bazy danych należy najpierw przekonwertować obraz bitmapowy na tablicę bajtów, a następnie zastosować go za pomocą zapytania do bazy danych.
2. Podczas pobierania z bazy danych z pewnością masz tablicę bajtów obrazu, co musisz zrobić, to przekonwertować tablicę bajtów z powrotem na oryginalny obraz. Musisz więc użyć BitmapFactory do dekodowania.

Poniżej znajduje się klasa Utility, która, mam nadzieję, może ci pomóc:

public class DbBitmapUtility {
 
    // convert from bitmap to byte array
    public static byte[] getBytes(Bitmap bitmap) {
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        bitmap.compress(CompressFormat.PNG, 0, stream);
        return stream.toByteArray();
    }
 
    // convert from byte array to bitmap
    public static Bitmap getImage(byte[] image) {
        return BitmapFactory.decodeByteArray(image, 0, image.length);
    }
}

Utwórz bazę danych z folderu zasobów

Umieść plik dbname.sqlite lub dbname.db w folderze zasobów projektu.

public class Databasehelper extends SQLiteOpenHelper {
        public static final String TAG = Databasehelper.class.getSimpleName();
        public static int flag;
        // Exact Name of you db file that you put in assets folder with extension.
        static String DB_NAME = "dbname.sqlite";
        private final Context myContext;
        String outFileName = "";
        private String DB_PATH;
        private SQLiteDatabase db;
    
        public Databasehelper(Context context) {
            super(context, DB_NAME, null, 1);
            this.myContext = context;
            ContextWrapper cw = new ContextWrapper(context);
            DB_PATH = cw.getFilesDir().getAbsolutePath() + "/databases/";
            Log.e(TAG, "Databasehelper: DB_PATH " + DB_PATH);
            outFileName = DB_PATH + DB_NAME;
            File file = new File(DB_PATH);
            Log.e(TAG, "Databasehelper: " + file.exists());
            if (!file.exists()) {
                file.mkdir();
            }
        }
    
        /**
         * Creates a empty database on the system and rewrites it with your own database.
         */
        public void createDataBase() throws IOException {
            boolean dbExist = checkDataBase();
            if (dbExist) {
                //do nothing - database already exist
            } else {
                //By calling this method and empty database will be created into the default system path
                //of your application so we are gonna be able to overwrite that database with our database.
                this.getReadableDatabase();
                try {
                    copyDataBase();
                } catch (IOException e) {
                    throw new Error("Error copying database");
                }
            }
        }
    
        /**
         * Check if the database already exist to avoid re-copying the file each time you open the application.
         *
         * @return true if it exists, false if it doesn't
         */
        private boolean checkDataBase() {
            SQLiteDatabase checkDB = null;
            try {
                checkDB = SQLiteDatabase.openDatabase(outFileName, null, SQLiteDatabase.OPEN_READWRITE);
            } catch (SQLiteException e) {
                try {
                    copyDataBase();
                } catch (IOException e1) {
                    e1.printStackTrace();
                }
            }
    
            if (checkDB != null) {
                checkDB.close();
            }
            return checkDB != null ? true : false;
        }
    
        /**
         * Copies your database from your local assets-folder to the just created empty database in the
         * system folder, from where it can be accessed and handled.
         * This is done by transfering bytestream.
         */
    
        private void copyDataBase() throws IOException {
            
            Log.i("Database",
                    "New database is being copied to device!");
            byte[] buffer = new byte[1024];
            OutputStream myOutput = null;
            int length;
            // Open your local db as the input stream
            InputStream myInput = null;
            try {
                myInput = myContext.getAssets().open(DB_NAME);
                // transfer bytes from the inputfile to the
                // outputfile
                myOutput = new FileOutputStream(DB_PATH + DB_NAME);
                while ((length = myInput.read(buffer)) > 0) {
                    myOutput.write(buffer, 0, length);
                }
                myOutput.close();
                myOutput.flush();
                myInput.close();
                Log.i("Database",
                        "New database has been copied to device!");
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    
        public void openDataBase() throws SQLException {
            //Open the database
            String myPath = DB_PATH + DB_NAME;
            db = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READWRITE);
            Log.e(TAG, "openDataBase: Open " + db.isOpen());
        }
    
        @Override
        public synchronized void close() {
            if (db != null)
                db.close();
            super.close();
        }
    
        public void onCreate(SQLiteDatabase arg0) {
    
        }
    
        @Override
        public void onUpgrade(SQLiteDatabase arg0, int arg1, int arg2) {
    
        }
    }

Oto, w jaki sposób możesz uzyskać dostęp do obiektu bazy danych do swojej działalności.

// Create Databasehelper class object in your activity.
   private Databasehelper db;

Następnie w metodzie onCreate zainicjuj ją i wywołaj metodę createDatabase (), jak pokazano poniżej.

db = new Databasehelper(MainActivity.this);
        try {
            db.createDataBase();
        } catch (Exception e) {
            e.printStackTrace();
        }

Wykonaj wszystkie operacje wstawiania, aktualizacji, usuwania i wybierania, jak pokazano poniżej.

String query = "select Max(Id) as Id from " + TABLE_NAME;
        db.openDataBase();
        int count = db.getId(query);
        db.close();

Eksportowanie i importowanie bazy danych

Możesz na przykład zaimportować i wyeksportować bazę danych do kopii zapasowych. Nie zapomnij o uprawnieniach.

public void exportDatabase(){
    try
    {
        File sd = Environment.getExternalStorageDirectory();
        File data = Environment.getDataDirectory();

        String currentDBPath = "//data//MY.PACKAGE.NAME//databases//MY_DATABASE_NAME";
        String backupDBPath = "MY_DATABASE_FILE.db";
        File currentDB = new File(data, currentDBPath);
        File backupDB = new File(sd, backupDBPath);

        FileChannel src = new FileInputStream(currentDB).getChannel();
        FileChannel dst = new FileOutputStream(backupDB).getChannel();
        dst.transferFrom(src, 0, src.size());
        src.close();
        dst.close();

        Toast.makeText(c, c.getResources().getString(R.string.exporterenToast), Toast.LENGTH_SHORT).show();
    }
    catch (Exception e) {
        Toast.makeText(c, c.getResources().getString(R.string.portError), Toast.LENGTH_SHORT).show();
        Log.d("Main", e.toString());
    }
}

public void importDatabase(){
    try
    {
        File sd = Environment.getExternalStorageDirectory();
        File data = Environment.getDataDirectory();

        String currentDBPath = "//data//" + "MY.PACKAGE.NAME" + "//databases//" + "MY_DATABASE_NAME";
        String backupDBPath = "MY_DATABASE_FILE.db";
        File backupDB = new File(data, currentDBPath);
        File currentDB = new File(sd, backupDBPath);

        FileChannel src = new FileInputStream(currentDB).getChannel();
        FileChannel dst = new FileOutputStream(backupDB).getChannel();
        dst.transferFrom(src, 0, src.size());
        src.close();
        dst.close();
        Toast.makeText(c, c.getResources().getString(R.string.importerenToast), Toast.LENGTH_LONG).show();
    }
    catch (Exception e) {
        Toast.makeText(c, c.getResources().getString(R.string.portError), Toast.LENGTH_SHORT).show();
    }
}

Wkładka luzem

Oto przykład wstawiania dużych porcji danych jednocześnie. Wszystkie dane, które chcesz wstawić, są gromadzone w tablicy ContentValues.

@Override
public int bulkInsert(Uri uri, ContentValues[] values) {
    int count = 0;
    String table = null;

    int uriType = IChatContract.MessageColumns.uriMatcher.match(uri);
    switch (uriType) {
        case IChatContract.MessageColumns.MESSAGES:
            table = IChatContract.MessageColumns.TABLE_NAME;
            break;
    }
    mDatabase.beginTransaction();
    try {
        for (ContentValues cv : values) {
            long rowID = mDatabase.insert(table, " ", cv);
            if (rowID <= 0) {
                throw new SQLException("Failed to insert row into " + uri);
            }
        }
        mDatabase.setTransactionSuccessful();
        getContext().getContentResolver().notifyChange(uri, null);
        count = values.length;
    } finally {
        mDatabase.endTransaction();
    }
    return count;
}

A oto przykład, jak go używać:

ContentResolver resolver = mContext.getContentResolver();
ContentValues[] valueList = new ContentValues[object.size()];
//add whatever you like to the valueList
resolver.bulkInsert(IChatContract.MessageColumns.CONTENT_URI, valueList);