[Grok-dev] Modeling a class that extend from list() with megrok.rdb
Hector Blanco
white.lists at gmail.com
Wed Oct 27 10:05:36 EDT 2010
Oh, now I see what you meant. Thanks!
But there's still a problem (sorry, I'm really new to this and I may
have the concepts wrong):
The class I want it to attack the "my_containers_table" table is
class MyContainer(list)
which currently extends from list (not rdb.Model).
Is there a way to have both functionalities? Do I have to go to
multiple inheritance? ( class MyContainer(list, rdb.Model) ).
Wouldn't that be "dangerous"? (I have been thought to avoid multiple
inheritance as the plague).
Do I have to do something like:
class MyContainer(rdb.Model):
def __init__(self):
self._list = list()
and use that self._list to store the data?
Thank you for your help!
2010/10/26 Jeffrey D Peterson <bgpete at gmail.com>:
>
>
> --
> Jeffrey Peterson
> bgpete3 at gmail.com
>
>> -----Original Message-----
>> From: grok-dev-bounces at zope.org [mailto:grok-dev-bounces at zope.org] On
>> Behalf Of Hector Blanco
>> Sent: Tuesday, October 26, 2010 4:16 PM
>> Cc: grok-dev at zope.org
>> Subject: Re: [Grok-dev] Modeling a class that extend from list() with
>> megrok.rdb
>>
>> Hi guys!
>>
>> Thank you for your answers.
>>
>> To Jeff Petterson>
>> That's doable, but I would like to avoid (if possible) creating
>> raw MySQL queries. It turns out I am working with a pre-existent code,
>> and the system doesn't really uses raw queries. It relies on
>> sqlalchemy + megrok.rdb and I'd like to keep it consistent (once
>> again, if possible). I have worked in other projects and I always
>> prefer going to the lowest level possible (SQL queries "by hand")
>> because I feel I can control them better, but not in this occasion.
>
> Who said anything about raw queries? It's SQLAlchemy.
>
> This (straight SQLAlchemy):
>
>> my_containers_table = Table(
>> "my_containers_table",
>> metadata,
>> Column("id", Integer, primary_key=True),
>> Column("my_entry_id", Integer, ForeignKey("my_entries_table.id"))
>> )
>
> Is equivalent to this (megrok.rdb and SQLAlchemy):
>
> from megrok import rdb
>
> from sqlalchemy import Column
> from sqlalchemy.types import Integer
> from sqlalchemy.orm import relation
>
> class MyContainersTable(rdb.Model):
> rdb.metadata(metadata)
> rdb.tablename('my_containers_table') #this is optional but I like to
> use it to be clear
>
> id = Column('id', Integer, primary_key=True)
> my_entry_id = relation('my_entry_id', Integer,
> ForeignKey('my_entries_table.id')
>
>
> This is how megrok.rdb uses sqlalchemy to map tables to python classes. It
> uses sqlalchemy's declarative modeling and builds this table for you in
> MySQL or if it already exists use rdb.reflected() to reflect it.
>
> Write all the methods you want to into the class to attack the table.
>
>>
>> To Santiago Videla>
>> I took a look to the containers, but they seem to me just
>> intermediate tables to define relationships, correct? Well... once
>> again, I have to deal with the pre-existing code. The guys that
>> developed it didn't use containers classes. The tables that were used
>> as intermediate tables to specify relationships where declared in a
>> lower level (only with sqlalchemy commands). To keep consistency with
>> the existing code, I'd like to be able to define that intermediate
>> tables myself.
>>
>> As I mentioned, the way I have it now is:
>>
>> class MyEntry(object):
>> def __init__(self):
>> self.field1 = “field1”
>> self.field2 = “field2”
>>
>> class MyContainer(list):
>> def __init__(self):
>> super(MyContainer,self).__init__()
>>
>> def append(myEntry):
>> if isinstance(myEntry, MyEntry):
>> super(MyContainer, self).append(myEntry)
>>
>> def getByField1(self, field1):
>> for element in self:
>> if element.field1 == field1:
>> return element
>> return None
>>
>> [ ... more useful methods ...]
>>
>> 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 "MyClass" classes descending from
>> (rdb.Model). I also see clearly the intermediate table for
>> MyContainer:
>>
>> #This would be the equivalent to a "rdb.Container", correct, Mr.
>> Videla? Well... in the current system, it is done "by hand", like
>> this:
>> my_containers_table = Table(
>> "my_containers_table",
>> metadata,
>> Column("id", Integer, primary_key=True),
>> Column("my_entry_id", Integer, ForeignKey("my_entries_table.id"))
>> )
>>
>> but I don't know how to link the MyContainer(list) object with
>> my_containers_table (and from there with MyClass) :-(
>>
>> I guess MyClass could be modeled with something like:
>>
>> class MyClass(rdb.Model):
>> rdb.metadata(metadata)
>> rdb.tablename("my_class_table")
>> id = Column("id", Integer, primary_key=True)
>> anotherField = Column("another_field", String(16))
>> container1 = Column("container_1", Integer,
>> ForeignKey("my_containers_table.id")),
>> container2 = Column("container_2", Integer,
>> ForeignKey("my_containers_table.id"))
>>
>> But now, how do 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 :-)
>>
>> I know... the existing code is a complicated mix between megrok and
>> sqlalchemy... but that's what I have to deal with (although if it
>> needs to be changed because there's no other way, well... I can do it)
>>
>> Thank you again
>>
>> 2010/10/26 Santiago Videla <santiago.videla at gmail.com>:
>> > Hi, I am not working with megrok.rdb these days neither with grok...
>> but,
>> > did you see rdb.Container and rdb.QueryContainer? I am not sure, but
>> maybe
>> > it could help you with this.
>> > Regards,
>> >
>> > On Mon, Oct 25, 2010 at 7:02 PM, Hector Blanco
>> <white.lists at gmail.com>
>> > wrote:
>> >>
>> >> Hi list!
>> >>
>> >> I am trying to migrate my application from ZopeDB to MySql. I am
>> using
>> >> megrok.rdb.
>> >>
>> >> I have a class which inherits from list() and has a few extra
>> methods.
>> >>
>> >> That class acts as a container of other classes and 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):
>> >> def __init__(self):
>> >> super(MyContainer,self).__init__()
>> >>
>> >> def append(myEntry):
>> >> if isinstance(myEntry, MyEntry):
>> >> super(MyContainer, self).append(myEntry)
>> >>
>> >> def getByField1(self, field1):
>> >> for element in self:
>> >> if element.field1 == field1:
>> >> return element
>> >> return None
>> >>
>> >> [ ... more useful methods ...]
>> >>
>> >> 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 don't really know how to model this with megrok.rdb. I kind of see
>> >> clearly (although I may be totally wrong) that MyEntry and MyClass
>> >> should extend from rdb.Model and each of them should be stored in a
>> >> table, but I don't really know what to do with “MyContainer”. I'd
>> like
>> >> to keep it inheriting from list, but I don't know how to model that.
>> >> It really only needs to be an association between [id,
>> id_of_my_entry]
>> >> (relationship 1:N). In MyClass, each of the containers would get an
>> id
>> >> and then, if I want to get the “MyEntries” that are in container1, I
>> >> just need to get the MyEntries who are linked to that id.
>> >>
>> >> … but I have no idea about how to implement that... Any hint I could
>> >> get would be deeply appreciated.
>> >>
>> >> Thank you in advance!
>> >> _______________________________________________
>> >> Grok-dev mailing list
>> >> Grok-dev at zope.org
>> >> https://mail.zope.org/mailman/listinfo/grok-dev
>> >
>> >
>> >
>> > --
>> > Santiago Videla
>> > http://www.linkedin.com/in/svidela
>> >
>> > Sigue la mata dando de que hablar siempre abajo y a la izquierda
>> donde el
>> > pensamiento que se hace corazón resplandece con la palabra sencilla y
>> > humilde que l at s tod at s somos.
>> >
>> _______________________________________________
>> Grok-dev mailing list
>> Grok-dev at zope.org
>> https://mail.zope.org/mailman/listinfo/grok-dev
>
>
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