Question

我有一个数据库和事件和时间表的表。我已将事件与时间表相关联。事件有时间表键列。现在我想删除一个时间表，当时间表被删除时，引用到各个时间表的事件应该被删除。这该怎么做？

我当前的删除查询是仅删除表而不删除事件。

    public void deleteTable(TimeTable timeTable) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_TIME_TABLE, KEY_TIME_TABLE_ID + " = ?",
            new String[]{String.valueOf(timeTable.getId())});
    db.close();
}

数据库助手

     public class DatabaseHelper extends SQLiteOpenHelper {



    private static final String TABLE_TIME_TABLE = "timetables";
    private static final String KEY_TABLE_TITLE = "tabletitle";
    private static final String KEY_TIME_TABLE_ID = "timetableid";
    private static final String KEY_TABLE_COLOR = "tablecolor";
    private static final String KEY_STATUS = "status";


    private static final String TABLE_EVENTS = "event";
    private static final String KEY_ID = "id";
    private static final String KEY_TITLE = "title";
    private static final String KEY_START_HOURS = "starthours";
    private static final String KEY_START_MINS = "startmins";
    private static final String KEY_END_HOURS = "endhours";
    private static final String KEY_END_MINS = "endmins";

    private static final String KEY_FROM_DATE = "datefrom";
    private static final String KEY_TO_DATE = "dateto";
    private static final String KEY_LOCATION = "location";
    private static final String KEY_DAY_OF_WEEK = "dayofweek";
    private static final String KEY_NOTIFICATION_TIME = "notification";

    private static final String KEY_COLOR = "color";


    private Context context;

    public DatabaseHelper(Context context) {
        super(context, Constants.DATABASE_NAME, null, Constants.DATABASE_VERSION);
        //3rd argument to be passed is CursorFactory instance
        this.context = context;
    }

    // Creating Tables
    @Override
    public void onCreate(SQLiteDatabase db) {


        createTable(db);

    }

    public void createDatabase(){
        context.deleteDatabase(Constants.DATABASE_NAME + ".db");
        SQLiteDatabase db = this.getReadableDatabase();
    }


    public void createTable(SQLiteDatabase db){
        String CREATE_EVENTS_TABLE = "CREATE TABLE " + TABLE_EVENTS + "("
                + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + KEY_TITLE + " TEXT,"
                + KEY_FROM_DATE + " DATE,"
                + KEY_TO_DATE + " DATE,"
                + KEY_DAY_OF_WEEK + " TEXT,"
                + KEY_LOCATION + " TEXT,"
                + KEY_NOTIFICATION_TIME + " DATE,"
                + KEY_TIME_TABLE_ID + " TEXT" + ")";

        db.execSQL(CREATE_EVENTS_TABLE);

        String CREATE_TIME_TABLE = "CREATE TABLE " + TABLE_TIME_TABLE + "("
                + KEY_TIME_TABLE_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + KEY_TABLE_TITLE + " TEXT,"
                + KEY_STATUS + " TEXT,"
                + KEY_TABLE_COLOR + " TEXT" + ")";

        db.execSQL(CREATE_TIME_TABLE);
    }

    // Upgrading database
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_EVENTS);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_TIME_TABLE);
        context.deleteDatabase(Constants.DATABASE_NAME + ".db");

        createTable(db);


        // Create tables again
        //onCreate(db);
    }

}

我尝试了这个内部删除查询，但它无效：

  public void delete(TimeTable t,int id)
{
    SQLiteDatabase db = this.getWritableDatabase();

    db.execSQL(" DELETE FROM " + TABLE_TIME_TABLE + " WHERE " + KEY_TIME_TABLE_ID + " == " + id + " IN "

    + " ( " + " SELECT * FROM " + TABLE + " WHERE " + KEY_TIME_TABLE_ID + " == " + id + " ) ");

    db.close();

}

有人可以帮忙吗？

谢谢..

Answer 1

有两种方法可以解决这个问题。第一个选项：修改deleteTable(TimeTable timeTable)函数以删除父记录和子记录。首先使用父ID删除子记录（事件），然后使用相同的id删除父记录（时间表）。这是一个样本。

public void deleteTable(TimeTable timeTable) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_EVENTS, KEY_TIME_TABLE_ID + " = ?",//KEY_TIME_TABLE_ID is a foreign key 
            new String[]{String.valueOf(timeTable.getId())});
    db.delete(TABLE_TIME_TABLE, KEY_TIME_TABLE_ID + " = ?",
            new String[]{String.valueOf(timeTable.getId())});
    db.close();
}

您可能希望将事件表中的KEY_TIME_TABLE_ID命名为FK_TIME_TABLE_ID 使代码更具可读性。

第二个选项：在创建表时使用删除级联定义外键（您也可以更改现有表并添加它们）。

String CREATE_EVENTS_TABLE = "CREATE TABLE " + TABLE_EVENTS + "("
        + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
        + KEY_TITLE + " TEXT,"
        + KEY_FROM_DATE + " DATE,"
        + KEY_TO_DATE + " DATE,"
        + KEY_DAY_OF_WEEK + " TEXT,"
        + KEY_LOCATION + " TEXT,"
        + KEY_NOTIFICATION_TIME + " DATE,"
        + KEY_TIME_TABLE_ID + " TEXT,"
        + " FOREIGN KEY (" + KEY_ID + ") references "
        + TABLE_TIME_TABLE + "(" + KEY_TIME_TABLE_ID + ") ON DELETE CASCADE)";

注意：默认情况下，sqlite不支持外键，因此每次连接数据库时都要运行以下查询。

PRAGMA foreign_keys = ON

这会启用外键

Answer 2

删除引用您要删除的时间表条目的事件。这样的事情：

DELETE FROM EVENTS WHERE TIMETABLE_ID=...

内部删除查询sqlite

2 个答案: