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.
