Android中使用SQLite的外键约束?在删除级联

2022-01-20 00:00:00 foreign-keys sqlite android java

我有两张表:tracks 和 waypoints，一个track 可以有很多waypoints，但是一个waypoint 只能分配给一个track.

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

在路点表中，我有一个名为trackidfk"的列，它会在创建轨道后插入 track_ID，但是我没有在此列上设置外键约束.

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.

当我删除一个轨迹时，我想删除分配的航点，这可能吗?我阅读了有关使用触发器的信息，但我认为 Android 不支持它们.

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.

创建航点表:

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"
                + " );"
              );

    ...
}

推荐答案

支持 on delete cascade 的外键约束，但您需要启用它们.
我刚刚在我的 SQLOpenHelper 中添加了以下内容，这似乎可以解决问题.

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;");
    }
}

我声明我的引用列如下.

I declared my referencing column as follows.

mailbox_id INTEGER REFERENCES mailboxes ON DELETE CASCADE

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