foreign key constraint ON DELETE CASCADE not worki

问题:

I have "days" table created as follows

"create table days(" +
            "day_id  integer primary key autoincrement, " +
            "conference_id integer , " +
            "day_date text, " +
            "day_start_time text, " +
            "day_end_time text, " +
            "day_summary text, " +
            "day_description text)";

and i have tracks table created as follows

CREATE_TABLE_TRACK = "create table track(" +
        "track_id integer primary key autoincrement," +
        "day_id integer,"+
        "track_name text," +
        "track_description text," +
        " FOREIGN KEY(day_id) REFERENCES days(day_id) ON DELETE CASCADE )";

as shown above i have foreign key day_id referencing to the day_id of table days...

So what i want is if i delete the day then corresponding track should also be deleted... But it does't happen in my case..

I have sqlite with version 3.5.9

And also i have added 1 line in my helper class as

> db.execSQL("PRAGMA foreign_keys=ON;");

but is still won't work.. please help me out..

回答1:

Cascading delete isn't supported until Sqlite version 3.6.19, which is first included on Android 2.2.

Fortunately there is an alternative.

You can execute another query like this below your create table query:

db.execSQL("CREATE TRIGGER delete_days_with track BEFORE DELETE ON track "
       +  "FOR EACH ROW BEGIN"
       +         " DELETE FROM days WHERE track.day_id = days.day_id "
       +  "END;");

Note that delete_days_with_track is just a name descriptive of what the trigger does, and this is just the pattern I use; I believe you could name it anything you wish.

回答2:

According to the SQLite Documentation support for Foreign Keys was not added until 3.6.19.

Using 3.5.9 you'll have to do your cascade deletions in some other manner.