Question

I’m testing the foreign keys in Android and I have problems I don’t understand:

To create the tables (with hard-coded values)

db.execSQL("CREATE TABLE IF NOT EXISTS table_A ( " +
            "_id long primary key , value1 long  );");
db.execSQL("CREATE TABLE IF NOT EXISTS table_B ( " +
            "_id long primary key , value1fk long  , value2 long,"+
            "FOREIGN KEY (value1fk) REFERENCES table_A (value1) ON DELETE CASCADE);");

then I execute:

    ContentValues values = new ContentValues();
    values.put("_id", 1);
    values.put("value1", 200);
    long result = mDb.insert("table_A", null, values);
    Log.e("","done (" + result + ")");


    values = new ContentValues();
    values.put("_id", 1);
    values.put("value1fk", 200);
    values.put("value2", 10);
    result= mDb.insert("table_B", null, values);
    Log.e("","done (" + result + ")");

The output is

done(1)
done(-1)

Giving the second insert an foreign key mismatch

E/SQLiteDatabase(25476): Error inserting _id=1 value1fk=200 value2=10
E/SQLiteDatabase(25476): android.database.sqlite.SQLiteException: foreign key mismatch: , while compiling: INSERT INTO table_B(_id,value1fk,value2) VALUES (?,?,?)

Why is that happening?

Answer 1

According to sqlite documentation on foreign keys
http://www.sqlite.org/foreignkeys.html
you need to either :

• use the primary key as your foreign key

  FOREIGN KEY (value1fk) REFERENCES table_A (_id)

• use a Unique column as a foreign key

  CREATE TABLE IF NOT EXISTS table_A (_id long primary key , value1 long UNIQUE);