Question

I am trying to create a table to only has a foreign key, not a primary key. I am getting this error:

java.lang.IllegalArgumentException: column '_id' does not exist

I read a tutorial that the primary key must be _id, with no explanation. And that is fine. But what if I do not want a primary key! What if I only want a foreign key. I am assuming this is where my problem lies. The schemas below are what I have. But the third one is where I assume this is coming from.

database.execSQL("CREATE TABLE events (" +
            "_id INTEGER PRIMARY KEY, event_name TEXT" +
            ")");

database.execSQL("CREATE TABLE reminders(_id INTEGER PRIMARY KEY, event_name TEXT" +
            ")");

database.execSQL("CREATE TABLE events_info (_id INTEGER, event_name TEXT, all_day INTEGER, " +
                    "start_date INTEGER, start_time INTEGER, end_date INTEGER, end_time INTEGER," +
                    " location TEXT, reminder_id INTEGER, notes TEXT, repeat TEXT," +
                    "FOREIGN KEY(_id) REFERENCES events(_id), FOREIGN KEY(reminder_id) REFERENCES reminders(_id))"
                    );

Answer 1

Are you using a CursorAdapter? Because if you are, the CursorAdapter class requires that there is a column named _id or else the class will not work. In general, it’s often considered good practice to have your database tables contain a column named _id for this reason, in case you ever decide to bind your data to a CursorAdapter or one of its subclasses.