http://grok.zope.org/documentation/how-to/orm-using-megrok.rdb-and-sqlalchemy
http://www.sqlalchemy.org/docs/ -- Jeffrey D Peterson Webmaster Crary Industries, Inc. 237 12th St NW West Fargo, ND 58078 P: 701-499-5928 E: jeff.peter...@crary.com > -----Original Message----- > From: sqlalchemy@googlegroups.com [mailto:sqlalch...@googlegroups.com] > On Behalf Of Hector Blanco > Sent: Tuesday, October 26, 2010 5:40 PM > To: sqlalchemy@googlegroups.com > Subject: [sqlalchemy] Containers/collections with SQLAlchemy > > Hi group! > > I am trying to migrate my application from ZopeDB to MySql. I am using > sqlalchemy under megrok.rdb. > > I have a class which inherits from list() and has a few extra methods. > Reading the chapter about custom collections in sqlalchemy > (http://www.sqlalchemy.org/docs/orm/collections.html#custom-collection- > implementations), > I thought that I'd be great having that class as a custom collection > (extending from list() but simulating a set(), where the items can't > be repeated) > > That class that extends from list, acts as a container of other > classes (mmm... yeah, as all the collections do... pretty obvious). It > is used (as an attribute) in other classes as well: > > class MyEntry(object): > def __init__(self): > self.field1 = "field1" > self.field2 = "field2" > > > class MyContainer(list): > __emulates__ = set > def __init__(self): > super(MyContainer,self).__init__() > > def add(self, myEntry): > if isinstance(myEntry, MyEntry): > if not(myEntry in self): > super(MyContainer, self).append(myEntry) > > def getByField1(self, field1): > for element in self: > if element.field1 == field1: > return element > return None > # [ ... > # more useful methods, > # overloading to make the list behave like a set, > # yada yada yada > # ...] > > > class MyClass(object): > def __init__(self): > self.container1 = MyContainer() > self.container2 = MyContainer() > self.anotherField = "hello world" > def getContainer1(): > return self.container1 > def getContainer2(): > return self.container2 > > I see clearly the "MyEntry" and (more or less clearly) "MyClass" > classes modeled in tables. > I also see clearly the intermediate table for MyContainer: > > my_containers_table = Table( > "my_containers_table", > metadata, > Column("id", Integer, primary_key=True), > Column("my_entry_id", Integer, ForeignKey("my_entries_table.id")) > ) > > So, in the MyClass class, each of MyContainer() instances can have an > id and when someone wants to retrieve the MyEntry() elements that are > in container1 (to say so), the "my_containers_table" can be used as a > middle table to get said MyEntries. > > but I don't know how to link the MyContainer(list) object with > my_containers_table (and from there with MyClass) :-( > > I'm not even sure whether MyClass.container1 and MyClass.container2 > should be ForeignKeys or Relations. > > How can I establish the relationship between MyClass.container1 or > MyClass.container2 with "my_containers_table"? > > On one hand, I want MyClass.container1 and MyClass.container2 to be > foreign keys, but on the other, I want them to be instances of > MyContainer(list)... And that's where I start banging my head on the > wall :-) > > In my mind (preferably before banging it against the wall) I see this > schema: > > +---Entry----+ > | id = 1 | > | "field1" | +----container1---+ > | "field2" | | id = 10 | > +-------------+ | foreign[0] = 1 | > | foreign[1] = 2 | +----- myClass > ----+ > +---Entry---+ +----------------------+ | id = 101 > | > | id = 2 | | > anotherField | > | "field1" | | > container1 = 10 | > | "field2" | +----container2---+ | container2 = 20 | > +-------------+ | id = 20 | +--------------- > ------+ > | foreign[0] = 3 | > +---Entry---+ +---------------------+ > | id = 3 | > | "field1" | > | "field2" | > +------------+ > > [I hope the Ascii thing is properly displayed] > > When I want to get all what is in myClass.container1, the system > should go to my_containers_table with the myClass.container1's id (10) > and retrieve all the "MyEntries" (id=1 and id=2 in the example above) > pointed by the ForeingKey of "my_containers_table". That's what I want > the system to do. But that's not what it's doing. > > Any tip will be deeply appreciated. Links to manuals, > documentations... whatever (I'm a total newbie in sqlmyalchemy) > > Thank you again! > > -- > You received this message because you are subscribed to the Google > Groups "sqlalchemy" group. > To post to this group, send email to sqlalch...@googlegroups.com. > To unsubscribe from this group, send email to > sqlalchemy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
