I have created a database for my android app which contains static data and does not require update/delete functionality thus when the app starts, I want to check if the db exists and if not then execute my dbAdapter class. I know its a simple if statement but I was just wondering the most efficient way to query whether the db exists.
Cheers
I'd rather check the existence of the file directly:
private static boolean doesDatabaseExist(Context context, String dbName) {
File dbFile = context.getDatabasePath(dbName);
return dbFile.exists();
}
/**
* Check if the database exist and can be read.
*
* @return true if it exists and can be read, false if it doesn't
*/
private boolean checkDataBase() {
SQLiteDatabase checkDB = null;
try {
checkDB = SQLiteDatabase.openDatabase(DB_FULL_PATH, null,
SQLiteDatabase.OPEN_READONLY);
checkDB.close();
} catch (SQLiteException e) {
// database doesn't exist yet.
}
return checkDB != null;
}
where DB_FULL_PATH is the path to your database file.
And the reason I am not just checking if a file exists is because it would not tell whether (a) it's an sqlite db file, (b) the file is not corrupt and can actually be read, i.e. due to partial download or however it has been created.
When you initialize the below class with:
mOpenHelper = new DatabaseHelper(getContext());
That will automatically create the database if it is not present. It also allows you upgrade the database by changing the DB_VER to a higher number.
Then so you are able to query the database use:
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
the above gets you db.query() & db.insert() etc methods.
private static class DatabaseHelper extends SQLiteOpenHelper {
private static final String DB_NAME = "db_name.db";
private static final int DB_VER = 1;
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VER);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL("CREATE TABLE table_name (" + "_id INTEGER PRIMARY KEY, "
+ " column_name_2 TEXT );");
.execSQL("INSERT INTO table_name "
+ "(column_name_2) "
+ "VALUES " + "('hello world');");
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.w(TAG + "Upgrading database from version " + oldVersion + " to "
+ newVersion + ", which will destroy all old data");
try {
db.execSQL("DROP TABLE IF EXISTS table_name");
onCreate(db);
} catch (SQLException e) {
Log.e(TAG + "getting exception "
+ e.getLocalizedMessage().toString());
}
}
}
I tried the version as provided by Mathias Conradt but I found that to simply check if DB != null is insufficient. I have amended to this:
/**
* Check if the database exist and can be read.
*
* @return true if it exists and can be read, false if it doesn't
*/
private boolean checkDataBase(String InDBFile) {
SQLiteDatabase checkDB = null;
boolean res = false;
try {
checkDB = SQLiteDatabase.openDatabase(InDBFile, null,
SQLiteDatabase.OPEN_READONLY);
res = (checkDB.getVersion() > 0);
checkDB.close();
} catch (SQLiteException e) {
// database doesn't exist yet.
Log.e("checkDataBase", "Selected file could not be opened as DB.");
res = false;
}
return res;
}
it's simple: Open your database in try block with path of da databse like:
try{
SQLiteDatabase dbe = SQLiteDatabase.openDatabase("/data/data/bangla.rana.fahim/databases/dictionary", null,0);
Log.d("opendb","EXIST");
dbe.close();
}
if an exception occurs then database doesn't exit so create it:
catch(SQLiteException e){
Log.d("opendb","NOT EXIST");
SQLiteDatabase db = openOrCreateDatabase("dictionary", MODE_PRIVATE, null);
db.execSQL("CREATE TABLE IF NOT EXISTS LIST(wlist varchar);");
db.execSQL("INSERT INTO LIST VALUES('খবর');");
db.execSQL("INSERT INTO LIST VALUES('কবর');"); //whatever you want
db.close();
}
that's it you are done :)
Create a global database helper class object in your main activity. In the MainActivity's onCreate() function try this:
//global database helper variable
DatabaseHelper dbh;
//in the onCreate()
if(dbh.getReadableDatabase()!=null)
//view the list
else
//create db
I have found an even simpler solution:
context.databaseList().contains("table_name")
