[Tutor] sqlite: don't understand a code snippet

[David]

Rich,

thanks a lot -- that was the problem.

David

Rich Lovely wrote:
> 2009/7/25 David <ldl08 at gmx.net>:
>   
>> Dear tutors,
>>
>> I am trying to teach myself the way Python's works with databases.
>> I decided to start with SQLite, and am looking at Summerfield's
>> 'Programming in Python 3'.
>> I got a code snippet that I don't fully understand (the comments are mine):
>>
>>
>> def get_and_set_director(db, director):
>>    # try to fetch existing director ID from db
>>    director_id = get_director_id(db, director)
>>    # if director ID was found in db, return ID
>>    if director_id is not None:
>>    return director_id
>> cursor = db.cursor()
>> # insert new director record
>> cursor.execute("INSERT INTO directors (name) VALUES (?)",
>>               (director,))
>> db.commit()
>> # retrieve and return new director ID from db
>> return get_director_id(db, director)
>>
>> Here is what I think is going on:
>>
>> The function get_and_set_director() gets the director ID from the db
>> by calling the function get_director-id() and returns its value.
>>
>> If the director ID is not in the db then, from outside the
>> get_and_set_director() function, the ID gets inserted to the db via
>> the commit() method. Finally, the director ID is returned (from the db)
>> by once again calling the get_director_id() function.
>>
>> Question: where does a new the director ID come from?
>>
>> Thanks for your directions!
>>
>> David
>>
>> _______________________________________________
>> Tutor maillist  -  Tutor at python.org
>> http://mail.python.org/mailman/listinfo/tutor
>>
>>     
>
> It sounds as if the directors table has an AUTO_INCREMENT column,
> which will automatically assign itself the next value sequentially
> when you insert an entry into the table.  i.e. The first inserted
> entry gets an ID of 1, the next 2, and so on.  This is stored in a
> column in the table.  The get_director_id(...) function will do
> something like the following query:
>
> cursor.execute("SELECT id FROM directors WHERE name == \"%s\"", (name,))
>
> I don't know how well I've explained it, but this is the normal
> technique for generating unique ids for rows in a database.
>
>