更新时间:2023-02-03 08:55:18
您的数据库应该删除 quizQuestions
行,以防有人从测验删除
或问题
。它会忽略的全部的情况下外键的支持外键约束关闭,您刚才常规列,可以包含任意值。
SQLite的默认设置为 PRAGMA foreign_keys = OFF
每次的的时间打开的数据库。这不是模式的表或属性。
如果你使用 SQLiteOpenHelper
把它放在的OnOpen
。这是被称为每次打开数据库时的地方。 的onCreate
仅在创建数据库时一次。
什么 SQLiteOpenHelper
要求当你调用 getWriteableDatabase
首次为
onConfigure
每一次,API等级> = 16要求的onCreate
如果没有数据库文件。通常情况下,这种情况只有一次在应用程序的整个生命周期。 onUpgrade
如果数据库版本( PRAGMA user_version
- 保存在数据库文件内部)小于该版本提供在SQLiteOpenHelper的构造函数。发生的每一次撞击的版本,在code。的OnOpen
每次如果 SQLiteOpenHelper
的相同实例已经有一个打开的数据库,它将只返回它并没有以上情况发生。
In Android 4.2, using SQLite 3.7.11, when I delete a row from the Quizzes table, who's schema is below, the corresponding rows in the QuizQuestions table are not deleted.
I can't figure out what's wrong. I have tried putting
db.execSQL("PRAGMA foreign_keys = ON;");
before and after the create table statements.
Create table statements:
CREATE TABLE quizzes(quiz_name TEXT PRIMARY KEY COLLATE NOCASE);
CREATE TABLE quizQuestions(quiz_name TEXT, question_id INTEGER,
PRIMARY KEY(quiz_name, question_id),
FOREIGN KEY(quiz_name) REFERENCES quizzes(quiz_name) ON DELETE CASCADE,
FOREIGN KEY(question_id) REFERENCES questions(question_id) ON DELETE CASCADE);
Your database should delete rows from quizQuestions
in case someone is deleting from quizzes
or from questions
. It will ignore the entire foreign key constraint in case foreign key support is turned off and you have just regular columns that can contain any value.
SQLite defaults to PRAGMA foreign_keys = OFF
every time you open the database. It's not a property of a table or of the schema.
In case you use SQLiteOpenHelper
put it in onOpen
. That is the place that is called every time the database is opened. onCreate
only once when the database is created.
What SQLiteOpenHelper
calls when you call getWriteableDatabase
for the first time is
onConfigure
every time, API Level >= 16 requiredonCreate
if there is no database file. Typically, this happens only once in the entire lifetime of the app.onUpgrade
if the database version (PRAGMA user_version
- saved inside the database file) is less then the version supplied in SQLiteOpenHelper's constructor. Happens every time you bump the version in your code.onOpen
every timeIf the same instance of SQLiteOpenHelper
already has an open database it will just return it and nothing of above happens.