Jason Porath wrote:
> I think a lot of my hesitation in this comes from worrying that
> Elixir will start messing around with the table structure. I'm
> still a little shaky as to what's going on under the hood, and
> when it will execute certain commands. A lot of what I'm having to
> do is bridge several tables at the same time, so I don't know how
> elixir would, say, commit that data, if the class I've given it
> isn't a 1-to-1 matchup with the table. Would it add any fields not
> in the table?
This is a big deficiency of Elixir right now, in that we don't
really document what is going on under the hood very well. And,
to answer your question, you really need to get the mappings 100%
perfect against your existing schema, or you are asking for trouble.
You can see what Elixir has generated by looking at the entity's
table object, which Elixir generates for you:
from elixir import *
class Person(Entity):
name = Field(String(32))
pets = OneToMany('Pet')
using_options(tablename='people')
class Pet(Entity):
name = Field(String(32))
owner = ManyToOne('Person')
using_options(tablename='pets')
setup_all()
# print out a representation of the table
# for the Person entity
print repr(Person.table)
# print out a representation of the table
# for the Pet entity
print repr(Pet.table)
The main things that Elixir will do to your schema behind the
scenes:
1. If you don't specify a primary key on your entity by passing
the `primary_key` keyword argument to one or more `Field`s on
your entity, one will be generated called `id`. To get around
this, simply specify the primary key using the aforementioned
keyword argument.
2. When you specify a `ManyToOne` relationship, this side of the
relationship will generate a foreign key field to the primary key
of the referenced entity automatically. You can read a bit more
about this in our documentation:
http://elixir.ematia.de/apidocs/elixir.relationships.html
Note that you can specify an alternate column name.
There are a few more things, such as entire tables being created
when you use `ManyToMany`, which I do not recommend (use an
association object instead). But these two are the big ones that you
need to know when you get started.
If you have a schema already in place and have a lot of trouble
mapping your tables appropriately, you might be better off using
plain SQLAlchemy. Elixir is great if you are starting fresh, but
might not be the best fit for you if you have an existing schema
which may not lend itself to Elixir's assumptions and design.
That being said, SQLAlchemy itself is designed specifically to
handle any schema you that throw at it. Its not quite as pretty, but
it sure is functional! I have projects that use Elixir, and other
projects that use plain-SQLAlchemy, depending on what ends up being
the best fit.
Best of luck.
--
Jonathan LaCour
http://cleverdevil.org
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