1. 在实体类中定义外键：

@Entity
public class User {
    @PrimaryKey
    public int userId;
    public String name;
}

@Entity
public class Book {
    @PrimaryKey
    public int bookId;
    public String title;
    @ForeignKey(entity = User.class, parentColumns = "userId", childColumns = "bookId")
    public int userId;
}

2. 在数据库中创建表格：

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("CREATE TABLE User (userId INTEGER PRIMARY KEY, name TEXT)");
    db.execSQL("CREATE TABLE Book (bookId INTEGER PRIMARY KEY, title TEXT, userId INTEGER, FOREIGN KEY(userId) REFERENCES User(userId))");
}

3. 在数据库升级和更改表时处理外键：

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    if (oldVersion < 2) {
        db.execSQL("ALTER TABLE Book ADD COLUMN userId INTEGER");
        db.execSQL("UPDATE Book SET userId=(SELECT userId FROM User WHERE name='default') WHERE userId IS NULL");
        db.execSQL("CREATE INDEX index_Book_userId ON Book(userId)");
        db.execSQL("FOREIGN KEY(userId) REFERENCES User(userId) ON DELETE CASCADE");
    }
}

以上步骤可以确保在更新表结构和数据库版本时不会破坏外键约束。