[Grok-dev] [MeGrok & SqlAlchemy] Simple relationship 1:1 fails with > "Foreign key assocated with column ------- could not find table" > (Hector Blanco)

[Kathy Manwaring]

Hi Hector,

Someone may have pointed this out already, but you have 'parent_table' in
the Child.py file, but 'parents_table' everywhere else...
I know this is not what the error message says, but it is probably part of
the problem.

Hope this helps!
Kathy

0406 911 985
kathy at perfectnotes.com.au
Perfect Notes I. T.

> Date: Fri, 29 Oct 2010 18:44:04 -0400
> From: Hector Blanco <white.lists at gmail.com>
> Subject: [Grok-dev] [MeGrok & SqlAlchemy] Simple relationship 1:1
> 	fails with "Foreign key assocated with column ------- could not find
> 	table"
> To: grok-dev at zope.org
> Message-ID:
> 	<AANLkTim4x8L0XQ18G6fZ-gBpbRNGFbYp_LgE30X9uQ+9 at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hello, list!
>
<snip>
> I am getting this error:
> Foreign key assocated with column 'children_table.id' could not find
> table 'parents_table' with which to generate a foreign key to target
> column 'id'
>
> I have a file, called Tables.py where all the classes and auxiliary
> (or intermediate) tables that I'm going to use in my application are
> defined:
>
> Tables.py >>
>
> class Parent(rdb.Model):
> 	rdb.metadata(metadata)
> 	rdb.tablename("parents_table")
>
> 	id = Column("id", Integer, primary_key=True)
> 	_whateverField= Column("whatever_field", String(16)) #Irrelevant
>
> 	child1 = relationship("Child", uselist=False)
>
> class Child(rdb.Model):
> 	rdb.metadata(metadata)
> 	rdb.tablename("children_table")
> 	id = Column("id", Integer, ForeignKey(Parent.id), primary_key = True)
> 	type = Column("type", String(2)) #Irrelevant (for this example)
>
> #A few lines below, said classes are "Grokified":
>
> def setComponents():
> 	"""Grok all the classes related to the database"""
> 	grok_component("Parent", Parent)
> 	grok_component("Child", Child)
> 	print "Grokified!"
>
> #This method is properly run... I see a "Grokified" message properly.
>
>      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> -
> And then I have two different Python .py files (Parent.py and
> Child.py) where the methods that manage said classes are implemented.
> In those files, the static area of each class is copied from Tables.py
> with some changes in the quotes (where I can use the object itself, I
> use it):
>
> Parent.py >>
>
> from child import Child
> metadata = rdb.MetaData()
>
> class Parent(rdb.Model):
> 	rdb.metadata(metadata)
> 	rdb.tablename("parents_table")
>
> 	id = Column("id", Integer, primary_key=True)
> 	_whateverField= Column("whatever_field", String(16)) #Irrelevant
>
> 	child1 = relationship(Child, uselist=False) #No quotation marks on this
> Child
>      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> -
> And
>
> Child.py > >
> metadata = rdb.MetaData()
>
> class Child(rdb.Model):
> 	rdb.metadata(metadata)
> 	rdb.tablename("children_table")

THIS NEXT LINE SEEMS TO HAVE THE WRONG NAME:

> 	id = Column("id", Integer, ForeignKey("parent_table.id"), primary_key =
> True)
> 	type = Column("type", String(2)) #Irrelevant (for this example)
>      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> -
>
> When I try to use these classes, I get:
> Foreign key assocated with column 'children_table.id' could not find
> table 'parents_table' with which to generate a foreign key to target
> column 'id'
>
> But if I take a look to the tables with a MySQL Query Browser, the
> table "parents_table" is there, happily and properly created.
>
> In some other places, I have had similar problems, but I've been able
> to fix them by delaying the imports. I had been able to (kind of)
> import the Parent type in the Child file so I can use the Parent
> object directly. It would be a little bit as if in this case I was
> able to do:
>
> from parent import Parent
> [ . . . ]
>
> class Child(rdb.Model):
>  	[ . . . ]
> 	id = Column("id", Integer, ForeignKey(Parent.id), primary_key = True)
>
> and that usually fixed the problem but in this specific case, I can't
> really do that: In the Parent file I need to import the Child and that
> gives a very, very nasty circular dependency problem.
>
> Is there a way to tell the Child.py file something like "Hey, dude...
> Here's the parent_table that you need!" ?  (Well... In a more Pythonic
> way, of course... I don't think 'dude'is a reserved keywork in Python,
> or an SqlAlchemy type). I don't know, something like:
>
> from whathever.repository.of.tables import parent_table
>
>          so I can, without quotes, use:
>
> id = Column("id", Integer, ForeignKey(parent_table.id), primary_key =
> True)
>
> (I guess that may work)
>
> I tried to figure out something out of these links:
> http://pypi.python.org/pypi/megrok.rdb (basic documentation)
> http://grok.zope.org/documentation/how-to/orm-using-megrok.rdb-and-sqlalchemy
>  (more advanced)
>
> but I still wasn't able to get anything. If anyone knows a good
> megrok.rdb tutorial, that would be very helpful as well...
> So I don't have to ask that much :-(
> "don't give a needy person a fish, give him a fish pole and teach him
> how to fish" ... type :-)
>
> Thank you!!
>
>
> ------------------------------