android.database.sqlite.SQLiteOpenHelper provides the ability to use an in-memory database if the name argument to its constructor is null:
String: of the database file, or null for an in-memory database
If SQLiteOpenHelper is instantiated multiple times with a null name argument, do they access the same in-memory database or is a separate in-memory database created each time?
From SQLite official documentation In-Memory Databases
Opening two database connections each with the filename ":memory:" will create two independent in-memory databases.
In Android, pass null instead of ":memory:"
So, If you instantiate SQLiteOpenHelper multiple times with a null name argument then it create separate in-memory database created each time
If we look at the source code, we see that in the constructor mName would get set to null.
public SQLiteOpenHelper(Context context, String name, CursorFactory factory, int version,
DatabaseErrorHandler errorHandler) {
if (version < 1) throw new IllegalArgumentException("Version must be >= 1, was " + version);
mContext = context;
mName = name;
mFactory = factory;
mNewVersion = version;
mErrorHandler = errorHandler;
}
Which means getDatabaseName() returns null.
public String getDatabaseName() {
return mName;
}
Later, through the use of getReadableDatabase() or getWritableDatabase(), if mName is null, then it calls the create method for an in-memory database instead of trying to opening one from disk.
if (mName == null) {
db = SQLiteDatabase.create(null); // in-memory
} else {
// db file opened or created
}
...
return db;
That db variable is maintained in the SQLiteOpenHelper until it is closed, which in the case of an in-memory database, means the data is deleted.
To clarify,
Each instance of a SQLiteOpenHelper that uses an in-memory database will its own database while the same instance will use one database and persist that data until it is closed.
I created sqlite database in android as shown in the code below and i added some records to it. then i wanted to copy that database to use it in anothe
application, my database is called "GEOLOC.db" and i searched for it but it was not found despite it contains data.
please let me know
1-how to know where the sqlite database is saved
2-can i specify a path to which the databse will be saved?
code:
public class SQLiteHelper extends SQLiteOpenHelper {
private final String TAG = this.getClass().getSimpleName();
private static final int DATABASE_VERSION = 2;
private static final String DATABASE_NAME = "GEOLOC.db";//can i specify a pth here??
private static final String DATABASE_TABLE_NAME = "NODE_00";
private Context mCtx = null;
public SQLiteHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
this.mCtx = context;
}
Usually, a particular sqlite database is specific to one single application. However you won't be able to view it unless the phone is rooted. In fact it is normally found in the following path:
//data/data/<Your-Application-Package-Name>/databases/<your-database-name>
The application package name can be accessed using the following code:
PACKAGE_NAME = getApplicationContext().getPackageName();
The database name is stored in the class which extends the SQLiteOpenHelperthrough the following declaration:
private static final String DATABASE_NAME = "buspass";
In order to share data between apps (provied that they have both been developed by you), you will need to specify a shared user id in the Manifest file of both apps.
Use the same DBAdapter in both apps. In the app that hosts the database, call the DBAdapter with the native context.
DBadapter hostDBAdapter = new DbAdapter(getApplicationContext());
performerDBadapter.open();
In the second app, access the database with the context of the database hosting app.
First, define the shared context:
Context sharedContext = null;
try {
sharedContext = this.createPackageContext("replace.with.host.package.name", Context.CONTEXT_INCLUDE_CODE);
if (sharedContext == null) {
return;
}
} catch (Exception e) {
String error = e.getMessage();
return;
}
Then open the DBAdapter with the shared context:
DbAdapter sharedDBadapter = new PerformerDbAdapter(sharedContext);
sharedDBadapter.open();
The manifest file should have the following code:
<manifest xmlns:android="http://schemas.android.com/apk/res/android" android:sharedUserId="my.app" ... >
Hope this helps :)
I am making an Android app to learn sqllite. Because I use 7 tables, I decided to create 7 class files in a folder "DBHelper", and want to make 7 files in a folder "DBadapter". Here what the structure looks like:
root
DBHelper: 7 helper files (ex: PersonHelper.java)
DBadapter: 7 adapter files (ex: PersonDAO.java)
But I get an error message with PersonDAO.java: "cannot be accessed from outside package", when I declared the object: "PersonHelper personHelper = new PersonHelper(context);" in the constructor.
Anyone has an idea how to fix that without putting all files in one folder? What is the standard in the industry when creating multiple large tables?
PS: The error is gone once I place all files in one directory.
public class PersonDAO {
private Context context;
//Database info
private static final String DATABASE_NAME = "MyDB";
private static final int DATABASE_VERSION = 1;
//Table helper info
public PersonHelper databaseHelper;
private SQLiteDatabase db = null;
//Constructors
PersonDAO(Context context) {
this.context = context;
databaseHelper = new PersonHelper(context); //Error: "cannot be accessed from outside package"
}
Your constructor of your PersonHelper is probably default like it is in your PersonDAO class. So it can only be accessed from the same package. You have to change it to public to access it from PersonDAO:
public PersonHelper(Context context){
...
}
In my app, I use...
myFilesDir = new File(Environment.getExternalStorageDirectory().getAbsolutePath()
+ "/Android/data/" + packageName + "/files");
myFilesDir.mkdirs();
This is fine and the resulting path is...
/mnt/sdcard/Android/data/com.mycompany.myApp/files
I need a SQLite DB which I want to store on the SD card so I extend SQLiteOpenHelper as follows...
public class myDbHelper extends SQLiteOpenHelper {
public myDbHelper(Context context, String name, CursorFactory factory, int version) {
// NOTE I prefix the full path of my files directory to 'name'
super(context, myFilesDir + "/" + name, factory, version);
}
#Override
public void onCreate(SQLiteDatabase db) {
// Create tables and populate with default data...
}
}
So far so good - the first time I call getReadableDatabase() or getWriteableDatabase() the empty DB is created on the SD card and onCreate() populates it.
So here's the problem - the app is in beta testing with maybe 5 or 6 people and, like me, they're running Android v2.2 and everything works fine. I have one tester, however, running v2.1 and when myDbHelper tries to create the DB on first use, it crashes with the following...
E/AndroidRuntime( 3941): Caused by: java.lang.IllegalArgumentException: File /nand/Android/data/com.mycompany.myApp/files/myApp-DB.db3 contains a path separator
E/AndroidRuntime( 3941): at android.app.ApplicationContext.makeFilename(ApplicationContext.java:1445)
E/AndroidRuntime( 3941): at android.app.ApplicationContext.openOrCreateDatabase(ApplicationContext.java:473)
E/AndroidRuntime( 3941): at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:193)
E/AndroidRuntime( 3941): at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:98)
E/AndroidRuntime( 3941): at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:158)
The path for the files directory is an odd one ("/nand") as it's internal memory although not the phone's own internal memory - but it is the path returned by getExternalStorageDirectory() for this device.
I can see three possible answers...
Although acceptable on v2.2, specifying a fully qualified path for DB name isn't recommended and will fail on earlier versions
Fully qualified paths are acceptable for SD card storage but the "/nand" path is being interpreted as 'internal' and only relative paths are acceptable in this case
Something else which I'm missing completely
If any or all of the above apply I'd appreciate it if somebody could help with how I should approach this.
Thanks.
You can use the SQLiteOpenHelper with a custom path if you provide a custom ContextClass and if you have write access in the target directory.
public class DatabaseHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 3;
.....
DatabaseHelper(final Context context, String databaseName) {
super(new DatabaseContext(context), databaseName, null, DATABASE_VERSION);
}
}
And here is the custom DatabaseContext class that does all the magic:
class DatabaseContext extends ContextWrapper {
private static final String DEBUG_CONTEXT = "DatabaseContext";
public DatabaseContext(Context base) {
super(base);
}
#Override
public File getDatabasePath(String name) {
File sdcard = Environment.getExternalStorageDirectory();
String dbfile = sdcard.getAbsolutePath() + File.separator+ "databases" + File.separator + name;
if (!dbfile.endsWith(".db")) {
dbfile += ".db" ;
}
File result = new File(dbfile);
if (!result.getParentFile().exists()) {
result.getParentFile().mkdirs();
}
if (Log.isLoggable(DEBUG_CONTEXT, Log.WARN)) {
Log.w(DEBUG_CONTEXT, "getDatabasePath(" + name + ") = " + result.getAbsolutePath());
}
return result;
}
/* this version is called for android devices >= api-11. thank to #damccull for fixing this. */
#Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory, DatabaseErrorHandler errorHandler) {
return openOrCreateDatabase(name,mode, factory);
}
/* this version is called for android devices < api-11 */
#Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory) {
SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name), null);
// SQLiteDatabase result = super.openOrCreateDatabase(name, mode, factory);
if (Log.isLoggable(DEBUG_CONTEXT, Log.WARN)) {
Log.w(DEBUG_CONTEXT, "openOrCreateDatabase(" + name + ",,) = " + result.getPath());
}
return result;
}
}
Update june 2012:
how does this work (#barry question):
Normal android apps have their local database files relative to the app folder. By using a customer context with overwritten getDatabasePath() the database is now relative to a different directory on the sd card.
Update feb 2015:
After replacing my old android-2.2 device with a new android-4.4 device I found out that my solution didn't work anymore.
Thanks to #damccull-s answer I was able to fix it. I have updated this answer so this should be a working example again.
Update may 2017:
Statistics: This aproach is used in more than 200 github projects
Historically, you have not been able to use paths with SQLiteOpenHelper. It only worked on simple filenames. I had not realized that they relaxed that restriction in Android 2.2.
If you wish to use databases on the SD card, and you wish to support Android 2.1 and earlier, you cannot use SQLiteOpenHelper.
Sorry!
k3b's answer is awesome. It got me working. However, on devices using API level 11 or higher, you may see it stop working. This is because a new version of the openOrCreateDatabase() method was added. It now contains the following signature:
openDatabase(String path, SQLiteDatabase.CursorFactory factory, int flags, DatabaseErrorHandler errorHandler)
This seems to be the method called by default on some devices with this method available.
In order to make this method work on these devices, you need to make the following alterations:
First, edit your existing method so that it simply returns the result of a call to the new method.
#Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode,
CursorFactory factory) {
return openOrCreateDatabase(name, mode, factory, null);
}
Second, add the new override with the following code.
#Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, CursorFactory factory, DatabaseErrorHandler errorHandler) {
SQLiteDatabase result = SQLiteDatabase.openOrCreateDatabase(getDatabasePath(name).getAbsolutePath(),null,errorHandler);
return result;
}
This code is very similar to k3b's code, but note that SQLiteDatabase.openOrCreateDatabase takes a String instead of a File, and I've used the version of it that allows for a DatabaseErrorHandler object.
user2371653's answere is very nice.
but I found a issue:
#Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode,
CursorFactory factory) {
return openOrCreateDatabase(name, mode, factory, null);
}
this may cause crasd, if install your app at android 2.x
so we can modify it like this
#Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode,
CursorFactory factory) {
return super.openOrCreateDatabase(getDatabasePath(name).getAbsolutePath(), mode, factory);
}
because android 2.x does not has the api
openOrCreateDatabase(String name, int mode,
CursorFactory factory, DatabaseErrorHandler errorHandler)
in my opinion I found a better solution on this side here (SQLite database on SD card) and wanted to inform you. Notice the entry in the constructor.
public class TestDB extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "usertest.db";
private static final int DATABASE_VERSION = 1;
public TestDB (Context context){
super(context, context.getExternalFilesDir(null).getAbsolutePath() + "/" + DATABASE_NAME, null, DATABASE_VERSION );
}
...
}
Quote from the user website:
"It will create the database in the app's folder on the sdcard: /sdcard/Android/data/[your_package_name]/files. In that way the database will be seen as part of the app by android and removed automatically if the user uninstalls the app."
"I my app I have a large database and it will in most cases not fit on old phones internal memory, e.g. HTC Desire. It runs great on the sdcard, and most apps are "moved to sdcard" themselves anyway so don't worry about the database not being accessible, because the app won't be accessible it self."
I have created database AddressBookMaster.db using Sqlite Browser and also create table AddressBook in mentioned database. But now problem is that I want to use this .db file in my application so where should I put this db file and how to fetch in application?
Is there any example or tutorial which can help to me?
You can put your Database file in the SDcard also. Use following code to use the Database from the SDCard.
File dbfile = new File("/sdcard/Your_db_File.db" );
SQLiteDatabase db = SQLiteDatabase.openOrCreateDatabase(dbfile, null);
The information contained in Using your own SQLite database in Android applications should have exactly what you are looking for.
You should note that while this is not really difficult it is not just a set of trivial commands that would be done outside of your application.
The information contained in "Using your own SQLite database in Android applications" is very userful for U and If U have db with more than 1024 bytes size then first split db into small parts and copy that all small dbs in your application dirrectory .
Use android-sqlite-asset-helper, to fill (initialize) the database of your app on installation
If You want to change the default folder of the database to sdcard:
public class MyApplication extends Application {
#Override
public void onCreate() {
SQLiteOpenHelper helper = ..
SQLiteDatabase db = helper.getWritableDatabase()
}
#Override
public File getDatabasePath(String name) {
return new File(getDatabasePathString(name));
}
#Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory) {
return super.openOrCreateDatabase(getDatabasePathString(name), mode, factory);
}
#Override
public SQLiteDatabase openOrCreateDatabase(String name, int mode, SQLiteDatabase.CursorFactory factory, DatabaseErrorHandler errorHandler) {
return super.openOrCreateDatabase(getDatabasePathString(name), mode, factory, errorHandler);
}
/*Put the default folder to store database of your application / or activity here */
public String getDatabasePathString(String name) {
return getExternalCacheDir()+ "/" + name+".db"; /* /storage/emulated/0/Android/data/com.my.app/cache */
}
}