On Mar 28, 1:01 pm, "King Simon-NFHD78" <[EMAIL PROTECTED]> wrote: > That compiles and appears to run in the small test program attached, but > if you look at the query generated when accessing the 'cs' property, it > doesn't actually use the join condition: > > SELECT c.id AS c_id, c.name AS c_name > FROM c, a_b, b_c > WHERE ? = a_b.a_id AND b_c.c_id = c.id ORDER BY a_b.oid > > ie. the a_b.b_id = b_c.b_id clause is missing. > > If you aren't keen on the 'viewonly' pattern, how would you recommend > doing this? Just by adding a normal python property and doing a query? > The main reason I like setting it up as a relation is for the potential > of making it eager-loading just by changing a single flag. theres adding a property, theres the "lazyloader" construct i proposed the other day but would have the same issues. also i showed someone how to stick a "lazy callable" directly on the class in the same way as a lazy loader, which is what the "lazyloader" construct would do. but none of those address the eager load. what it might require is just that when "viewonly" is present it is less strict about finding foreign keys...since to generate the lazy clause, all it really needs is the "remote_side" to figure out where to stick the bind params. so i will look into that...then you wouldnt need to worry about sticking the "secondary" back in tehre which i think is too complicated anyway. > > Thanks, > > Simon > > ________________________________ > > From: sqlalchemy@googlegroups.com [mailto:[EMAIL PROTECTED] > On Behalf Of Michael Bayer > Sent: 28 March 2007 17:19 > To: sqlalchemy@googlegroups.com > Subject: [sqlalchemy] Re: Confused by foreign_keys argument > > what it cant locate are foreign keys between the parent and child > tables, "a" and "c"....because there arent any. when you have a > many-to-many, the rules for figuring out the relationship change, and it > knows to do that by the presence of the "secondary" argument. > > so if you can manufacture a "secondary" table you can do this: > > secondary = a_b_table.join(b_c_table, > onclause=a_b_table.c.b_id==b_c_table.c.b_id) > mapper( > A, a_table, > properties={'cs': relation(C, secondary=secondary, > primaryjoin=a_table.c.id==secondary.c.a_b_a_id, > secondaryjoin=secondary.c.b_c_c_id==c_table.c.id, > viewonly=True, > ) > } > ) > > im not totally sure the lazy clause is going to work but try it out. > > this goes back to my general dislike of "viewonly" and how i cant > generally support it, becuase as the rules for relationships get more > strict and accurate, cases like these become harder to model. > > On Mar 28, 2007, at 10:39 AM, King Simon-NFHD78 wrote: > > a_table = Table('a', metadata, > > Column('id', Integer, primary_key=True), > > Column('name', String(16)), > > ) > > b_table = Table('b', metadata, > > Column('id', Integer, primary_key=True), > > Column('name', String(16)), > > ) > > c_table = Table('c', metadata, > > Column('id', Integer, primary_key=True), > > Column('name', String(16)), > > ) > > a_b_table = Table('a_b', metadata, > > Column('a_id', Integer, ForeignKey('a.id'), > > primary_key=True), > > Column('b_id', Integer, ForeignKey('b.id'), > > primary_key=True), > > ) > > b_c_table = Table('b_c', metadata, > > Column('b_id', Integer, ForeignKey('b.id'), > > primary_key=True), > > Column('c_id', Integer, ForeignKey('c.id'), > > primary_key=True) > > ) > > class A(object): > > pass > > class B(object): > > pass > > class C(object): > > pass > > mapper(B, b_table) > > mapper(C, c_table) > > ############################################################# > > # How can I create a mapper on A with a property that gives > > # all the 'C' objects? > > ############################################################# > > # This doesn't work - it requires the foreign_keys parameter > > # to be passed, but I don't know what to pass. > > mapper( > > A, a_table, > > properties={'cs': relation(primaryjoin=and_(a_table.c.id == > > a_b_table.c.a_id, > > a_b_table.c.b_id > == > > b_c_table.c.b_id, > > c_table.c.id == > > b_c_table.c.c_id), > > viewonly=True, > > ) > > } > > ) > > join2.py > 3KDownload --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
