On Jul 19, 2010, at 12:04 PM, Harry Percival wrote:
> Michael, thanks, as ever, for your help.
>
> So, I think I've managed to specify the relationships:
>
>>>>
> j = join(movies_table,md_table).join(directors_table).join(genres_table)
> js = j.select(use_labels=True).alias('mdg')
>
> r0 = relationship(Movies,
> primaryjoin=(js.c.movies_movie_id==movies_table.c.movie_id),
> foreign_keys=([js.c.movies_movie_id])
> )
> r1 = relationship(Directors,
>
> primaryjoin=(js.c.directors_director_id==directors_table.c.director_id),
> foreign_keys=([js.c.directors_director_id])
> )
> r2 = relationship(Genres,
> primaryjoin=(js.c.genres_genre_id==genres_table.c.genre_id),
> foreign_keys=([js.c.genres_genre_id])
> )
>
> mapper(MoviesAndDirectorsAndGenres,
> js,
> properties={'movie':r0,
> 'director':r1,
> 'genre':r2
> },
> passive_updates=False)
>
>
> To test it, I'm trying to create a new composite object, based on a
> new movie but existing director & genre:
>
>
>>>>
> session=Session()
>
> m_new = Movies()
> m_new.id=8
> m_new.title = 'new movie'
> session.add(m_new)
>
> d2 = session.query(Directors).get(2)
> print '***************director=',d2
> g6 = session.query(Genres).get(6)
> print '***************genre=',g6
>
> oo_new = MoviesAndDirectorsAndGenres()
> oo_new.movie = m_new
> oo_new.director = d2
> oo_new.genre = g6
>
> try:
> # another_new = session.merge(new)
> session.merge(oo_new)
>
> but sqla is doing some really weird stuff:
>
> 2010-07-19 16:56:01,877 INFO sqlalchemy.engine.base.Engine.0x...37f0 BEGIN
> 2010-07-19 16:56:01,878 INFO sqlalchemy.engine.base.Engine.0x...37f0 INSERT
> INTO
> movies (movie_id, title, description, genre_id, release_date) VALUES
> (?, ?, ?,?, ?)
> 2010-07-19 16:56:01,880 INFO sqlalchemy.engine.base.Engine.0x...37f0
> (8, 'new movie', None, None, None)
> 2010-07-19 16:56:01,882 INFO sqlalchemy.engine.base.Engine.0x...37f0
> SELECT directors.director_id AS directors_director_id, directors.name
> AS directors_name
> FROM directors
> WHERE directors.director_id = ?
> 2010-07-19 16:56:01,885 INFO sqlalchemy.engine.base.Engine.0x...37f0 (2,)
> ***************director= <test_multitable.Directors object at 0x021E2030>
> 2010-07-19 16:56:01,888 INFO sqlalchemy.engine.base.Engine.0x...37f0
> SELECT genres.genre_id AS genres_genre_id, genres.name AS genres_name,
> genres.description AS genres_description
> FROM genres
> WHERE genres.genre_id = ?
> 2010-07-19 16:56:01,891 INFO sqlalchemy.engine.base.Engine.0x...37f0 (6,)
> ***************genre= <test_multitable.Genres object at 0x021E21B0>
> 2010-07-19 16:56:01,894 INFO sqlalchemy.engine.base.Engine.0x...37f0
> INSERT INTO genres (genre_id, name, description) VALUES (?, ?, ?)
> 2010-07-19 16:56:01,895 INFO sqlalchemy.engine.base.Engine.0x...37f0
> (6, None, None)
> 2010-07-19 16:56:01,898 INFO sqlalchemy.engine.base.Engine.0x...37f0 ROLLBACK
>
> attempted to add new composite object, failed with (IntegrityError)
> PRIMARY KEY must be unique u'INSERT INTO genres (genre_id, name,
> description) VALUES (?, ?, ?)' (6, None, None)
>
> Traceback (most recent call last):
> File "test_multitable.py", line 105, in <module>
> session.commit()
> File "sqlalchemy\orm\session.py", line 653, in commit
> <etc etc>
> IntegrityError: (IntegrityError) PRIMARY KEY must be unique u'INSERT INTO
> genres
> (genre_id, name, description) VALUES (?, ?, ?)' (6, None, None)
>
>
> it seems to trying to insert a new genre, even though I've told it to
> use an existing one?
>
> I suppose, once I've done the insert into the movies table, i could
> retrieve the new composite object via a session.query, instead of
> trying to do a session.merge. but this wouldn't work for creating a
> new Director object, since I also need to create an entry into the
> bridging table, something i'm hoping sqla could manage for me...
if you say x = new Foo() x.id = 7; session.add(x); that is an INSERT, no matter
what the ID is, and will fail as above if that primary key already exists. If
you OTOH say x = session.merge(x), it will be an INSERT or an UPDATE depending
on whether or not primary key id #7 exists in the database already or not.
You can get an overview of what the various methods do at:
http://www.sqlalchemy.org/docs/session.html#id1
>
> rgds,
> hp
>
>
> On Mon, Jul 19, 2010 at 3:31 PM, Michael Bayer <mike...@zzzcomputing.com>
> wrote:
>>
>> On Jul 19, 2010, at 10:24 AM, Harry Percival wrote:
>>
>>> OK, so I will treat any classes mapped to a join of multiple tables as
>>> being a read-only API, and manually manage the write-API using
>>> relationship().
>>>
>>> It doesn't look like I can define a relationship from the composite
>>> mapped class to individual tables though?
>>>
>>>>>>
>>> #single table mappers:
>>> mapper(Movies,movies_table)
>>> mapper(Directors,directors_table)
>>> mapper(Genres,genres_table)
>>>
>>>
>>> j = join(movies_table,md_table).join(directors_table).join(genres_table)
>>> r0 = relationship(Movies,
>>> primaryjoin=(movies_table.c.movie_id==md_table.c.movie_id),
>>> foreign_keys=([md_table.c.movie_id]))
>>> r1 =
>>> relationship(Directors)#,primaryjoin=(and_(movies_table.c.movie_id==md_table.c.movie_id,md_table.c.director_id==directors_table.c.director_id)))#,secondaryjoin=(md_table.c.director_id==directors_table.c.director_id),secondary=md_table)
>>> r2 = relationship(Genres)
>>>
>>> mapper(MoviesAndDirectorsAndGenres,
>>> j.select(use_labels=True).alias('mdg'),
>>
>> j.select(...).alias() is the selectable that you have to define all your
>> primaryjoins against. So you need to assign that on the outside to a
>> variable first.
>>
>>
>>
>>
>>
>>> properties={'movie':r0,
>>> 'director':r1,
>>> 'genre':r2
>>> },
>>> passive_updates=False)
>>>
>>> Tried lots of permutations of this, but it doesn't look like I can get
>>> sqla to understand a 1-to-1 relationship between the
>>> multiple-table-mapped MoviesAndDirectorsAndGenres objects and the
>>> Movies, Directors, or Genres objects they're built out of...
>>>
>>> I think perhaps I'm just trying to do something that SQLA really
>>> wasn't designed for...
>>>
>>> hp
>>>
>>> On Mon, Jul 19, 2010 at 2:29 AM, Michael Bayer <mike...@zzzcomputing.com>
>>> wrote:
>>>>
>>>> On Jul 15, 2010, at 5:11 PM, Harry Percival wrote:
>>>>
>>>>> thanks Michael. I really appreciate your help.
>>>>>
>>>>> How should use .merge()? I've tried both:
>>>>>>>>
>>>>> another_new = MoviesAndDirectorsAndGenres() #init another_new as blank row
>>>>> another_new = session.merge(new) #attempt to merge with my 'new'
>>>>> object that has desired attributes
>>>>>
>>>>> and
>>>>>>>>
>>>>> new = session.merge(another_new) #attempt to merge blank object to my
>>>>> new object with desired attributes
>>>>>
>>>>> the former fails trying to add a genre row that already exists, the
>>>>> latter fails trying to add an object with all null values.
>>>>>
>>>>> the thing is, I'm really not trying to merge anything. I'm trying to
>>>>> create a new object, which happens to be made up partially of new
>>>>> entries in some tables, and existing entries in other tables.
>>>>> genres_genre_id refers to the primary key of the genres table, and a
>>>>> genre with genre_id=6 already exists.
>>>>>
>>>>>
>>>>> am i going to have to map an ORM class to each of the composite
>>>>> tables, and use references to them via relationship() instead of
>>>>> hoping sql can figure it out by itself from the tables that make up
>>>>> the join construct?
>>>>>
>>>>> can supply a sqlite database and some source code if it helps?
>>>>
>>>> It's typically appropriate to map tables individually and connect them via
>>>> relationship(), if you want to be writing rows to them independently.
>>>> That's what the phrase "partially of new entries in some tables, and
>>>> existing entries in other tables." implies.
>>>>
>>>>
>>>>
>>>>>
>>>>> rgds,
>>>>> Harry
>>>>>
>>>>> On Thu, Jul 15, 2010 at 9:48 PM, Michael Bayer <mike...@zzzcomputing.com>
>>>>> wrote:
>>>>>>
>>>>>> On Jul 15, 2010, at 2:52 PM, Harry Percival wrote:
>>>>>>
>>>>>>> A new problem, which seems to occur in both IronPython and normal
>>>>>>> Python:
>>>>>>>
>>>>>>> I have a database with tables for movies, directors, genres (and a
>>>>>>> bridging table movie_directors)
>>>>>>> I have a class mapped to a join of all three of the above
>>>>>>>
>>>>>>>>>>
>>>>>>> j = join(movies_table,md_table).join(directors_table).join(genres_table)
>>>>>>> mapper(MoviesAndDirectorsAndGenres,j.select(use_labels=True).alias('moviesdirectorsgenres'))
>>>>>>>
>>>>>>> this works fine. i can query the database ok using this mapper.
>>>>>>>
>>>>>>> The tables already have some values in.
>>>>>>> Now, I want to create a new composite object, that references some of
>>>>>>> the existing values, but not all - say it's a new movie by an existing
>>>>>>> director in an existing genre:
>>>>>>>
>>>>>>>>>>
>>>>>>> new = MoviesAndDirectorsAndGenres()
>>>>>>> new.movies_movie_id=8 #does not already exist in the table
>>>>>>> new.directors_director_id=2 #already exists in the table
>>>>>>> new.genres_genre_id=6 #already exists too
>>>>>>> session.add(new)
>>>>>>>
>>>>>>> this fails with a constraint error / integrity error, because SQLA
>>>>>>> tries to re-insert genre #6 even though it already exists. it also
>>>>>>> happens if i use session.merge(new). it also happens if i fully
>>>>>>> specify all of the attributes of each movie/director/genre correctly.
>>>>>>>
>>>>>>> Is this expected behaviour? is there any way to get sqla to
>>>>>>> intelligently only do inserts when necessary? is it something to do
>>>>>>> with cascade configuration, and if so, how do i configure cascades on
>>>>>>> a mapper that's not based on relationship() but based on join()?
>>>>>>
>>>>>> you should be using merge(), and you should ensure that the objects
>>>>>> being merged have the correct primary key values. If "genre #6" refers
>>>>>> to some other column that isn't the primary key of that row, then you'd
>>>>>> have to ensure you put the correct primary key value on your object
>>>>>> first before merging it.
>>>>>>
>>>>>> you can always check what decision merge() made by asking, "obj in
>>>>>> session.new" versus "obj in session.dirty".
>
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