Foreign key constraints in Android using SQLite? on Delete cascade

jcrowson picture jcrowson · Mar 30, 2010 · Viewed 66k times · Source

I have two tables: tracks and waypoints, a track can have many waypoints, but a waypoint is assigned to only 1 track.

In the way points table I have a column called "trackidfk" which inserts the track_ID once a track is made, however I have not setup Foreign Key constraints on this column.

When I delete a track I want to delete the assigned waypoints, is this possible?. I read about using Triggers but I don't think they are supported in Android.

To create the waypoints table:

public void onCreate(SQLiteDatabase db) {
    db.execSQL( "CREATE TABLE " + TABLE_NAME 
                + " (" 
                + _ID         + " INTEGER PRIMARY KEY AUTOINCREMENT, " 
                + LONGITUDE   + " INTEGER," 
                + LATITUDE    + " INTEGER," 
                + TIME        + " INTEGER,"
                + TRACK_ID_FK + " INTEGER"
                + " );"
              );

    ...
}

Answer

Phil picture Phil · Jul 16, 2010

Foreign key constraints with on delete cascade are supported, but you need to enable them.
I just added the following to my SQLOpenHelper, which seems to do the trick.

@Override
public void onOpen(SQLiteDatabase db) {
    super.onOpen(db);
    if (!db.isReadOnly()) {
        // Enable foreign key constraints
        db.execSQL("PRAGMA foreign_keys=ON;");
    }
}

I declared my referencing column as follows.

mailbox_id INTEGER REFERENCES mailboxes ON DELETE CASCADE