sqlite 当你用外键删除一行时 id 会发生什么？

Question

I have these two tables:

class User(Base):
    """ User entry in database """
    __tablename__ = "users"
    # ID uniquely identifies 
    id             = Column(Integer, primary_key=True, index=True)
    kerberos       = Column(String, unique=True, index=True)
    hashpass       = Column(String)
    is_active      = Column(Boolean, default=True)
    creation_date  = Column(DateTime, default=None)

    scores = relationship("Score", back_populates="owner")

class Score(Base):
    """ Stores each users scores """
    __tablename__ = "scores"
    
    id    = Column(Integer, primary_key=True, index=True)
    user_id = Column(String, ForeignKey("users.id"), index=True)    
    score = Column(Integer)
    time = Column(DateTime)
    
    owner = relationship("User", back_populates="scores")

I have read that adding new "Users" will auto-increment the "id" field. Now each entry in the "scores" table has a foreign key pointing to users.id. This means (correct me if I'm wrong), that each "score" entry maps to one and only unique User (so the score:user relationship is many:one).

I'm wondering if this is a good design, especially if I delete a user, what happens? Does deleting a user automatically invalidate/delete the corresponding scores that are linked thru the deleted user's id (foreign key for those scores)? I am concerned that deleting a user will all user id's afterwards to shift down by one, so there would be an off by one issue when looking at a user's scores.

Is this good design? Feel free to link resources/redirect to another question (I couldn't not find any specifically)

Answer 1

I'm wondering if this is a good design, especially if I delete a user, what happens?

As it stands you would not be able to delete the User(s) as a Foreign Key Conflict would result. If you didn't have the FK constraint, protecting the referential integrity, then you would orphan the Scores (they would have no parent) which could result in unanticipated results and perhaps crashes.

To be able to delete a User, I believe that you could use ForeignKey("users.id", onupdate="CASCADE", ondelete="CASCADE")

Then deleting a User (parent) will then CASCADE the deletion, thus deleting the children (Scores that link to that specific parent) due to onDelete="CASCADE" .

Should you ever change a User's id value, then the user_id in the children would be changed (ie the update to the id will CASCADE down to the children).

I am concerned that deleting a user will all user id's afterwards to shift down by one,

No they will not, unless you make them (which you would probably would not want to do). However, with the onUpdate action as CASCADE if id's were changed the changes to the id would be CASCADEd.

• There are options (actions) see https://sqlite.org/foreignkeys.html#fk_actions