使用SQLite在Android的外键约束？ Delete（删除）级联 [英] Foreign key constraints in Android using SQLite? on Delete cascade

问题描述

我有两个表：曲目和航点，轨迹可以有多个航点，而是一个航点分配到只有1个轨道。

在路上积分榜我有一个名为trackidfk的插入track_ID一旦轨道由专栏，但是我还没有建立外键约束在此列。

当我删除曲目我想删除指定的航点，这是可能的？我读了有关使用触发器，但我不认为他们在Android的支持。

要创建的航点表：

 公共无效的onCreate（SQLiteDatabase DB）{
    db.execSQL（CREATE TABLE+ TABLE_NAME
                +（
                + _ID +INTEGER PRIMARY KEY AUTOINCREMENT，
                +经度+INTEGER
                +纬度+INTEGER
                +时间+INTEGER
                + TRACK_ID_FK +整数
                +）;
              ）;

    ...
}
 

解决方案

与删除级联外键约束的支持，但你需要启用它们。
我只是增加了以下我的 SQLOpenHelper 的，这似乎这样的伎俩。

  @覆盖
公共无效的OnOpen（SQLiteDatabase DB）{
    super.onOpen（DB）;
    如果（！db.isReadOnly（））{
        //启用外键约束
        db.execSQL（杂foreign_keys = ON;）;
    }
}
 

我宣布我引用列如下：

  mailbox_id INTEGER参考邮箱ON DELETE CASCADE
 

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"
                + " );"
              );

    ...
}

解决方案

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

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