On Aug 21, 2:17 am, "King Simon-NFHD78" <simon.k...@motorola.com>
wrote:
> darkblueB wrote:
>
> > ok, I have done this
> > I have an object def and a __table__ for all of the "main actors" in
> > my setup
> > I defined an __init__() for one of them
> > I use the declarative base
>
> > when the objects get created, they seem to have a __mapper__ in them
> > already
> > (the "primary mapper")
>
> > but when I do simple queries that would draw upon a foreign key
> > constraint present in the DB
> > I dont get any lookups
>
> > for example, (attribute? - I dont know all the terms here)
> > //meta is setup already, sqlite
> > // read in an existing DB
> > cBase = declarative_base(metadata=meta)
>
> > class saProject(cBase):
> > __table__ = meta.tables['bt_projects']
>
> > def __init__(self, inName, inFacilName, inImpModifier="",
> > inProbModifier="", inIsInviteOnly=0, inAllowWt=0, inAllowEvtSummary=1,
> > inAllowAssSum=1, inShowEvtRateAuth=1, inShowEvtRateCom=1 ):
> > self.name = inName
> > self.facilitator = inFacilName
> > self.impact_mod = inImpModifier
> > self.prob_mod = inProbModifier
> > .....
>
> > so now, I read one project in to tProj
> > tProj.name => 'FBLS'
>
> > but
> > tProj.impact_mod => Decimal("0")
> > *not* a lookup with the foreign key
>
> > here is the relevant SQL CREATE DB
>
> > CREATE TABLE 'bt_projects' (
> > name TEXT UNIQUE,
> > facilitator TEXT,
> > active NUMERIC DEFAULT 1,
> > impact_mod NUMERIC DEFAULT 0,
> > prob_mod NUMERIC DEFAULT 0,
> > ....
> > key INTEGER NOT NULL PRIMARY KEY,
> > FOREIGN KEY (impact_mod) REFERENCES bt_evt_prob_modifiers(key),
> > FOREIGN KEY (prob_mod) REFERENCES bt_evt_impact_modifiers(key)
> > );
>
> > so, I have to make an explicit mapper, too?
> > perhaps I am missing something
> > -Brian
>
> The "lookup with foreign key" that you are asking for is what SQLALchemy
> calls a "relation"
> (Seehttp://www.sqlalchemy.org/docs/05/ormtutorial.html#building-a-relation).
> You have to create them explicitly, and they can't have the same name as
> the foreign key itself. When the foreign keys are simple, SA can
> normally figure out the join conditions by itself.
>
> For example, to get the behaviour your were expected, your class
> definitions should look something like this:
>
> import sqlalchemy.orm as saorm
>
> class saEvtProbModifiers(cBase):
> __table__ = meta.tables['bt_evt_prob_modifiers']
>
> class saEvtImpactModifiers(cBase):
> __table__ = meta.tables['bt_evt_impact_modifiers']
>
> class saProject(cBase):
> __table__ = meta.tables['bt_projects']
>
> prob_modifier = saorm.relation(saEvtProbModifiers)
> impact_modifier = saorm.relation(saEvtImpactModifiers)
>
> Now when you access tProj.impact_modifier, you should get an instance of
> the saEvtImpactModifiers class.
>
> The relation function gies you lots of other options. You can configure
> a 'back reference' (so you could automatically add a 'projects' property
> to saEvtImpactModifiers and saEvtProbModifiers for example). You can
> also explicitly define the join conditions if SA is unable to work them
> out.
>
> It's worth working through the ORM tutorial
> (http://www.sqlalchemy.org/docs/05/ormtutorial.html) which covers all of
> this.
>
ok, some of that sounds familiar naturally, I built this database app
I am trying to replace!
but I thought somehow that meta.reflect() would pick up on the fk
constraints ...
ok - I will press on here
> Hope that helps,
>
thank you I appreciate your response
> Simon
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