Re: [sqlalchemy] Re: Foreign Keys and 'backref'

2014-07-31 Thread Rich Shepard 

On Thu, 31 Jul 2014, Jonathan Vanasco wrote:


backref indicates the string name of a property to be placed on the
related mapper’s class that will handle this relationship in the other
direction. The other property will be created automatically when the
mappers are configured. Can also be passed as a backref() object to
control the configuration of the new relationship.

Using your examples side-by-side:

user = relationship(User, backref=backref('addresses', order_by=id))
addresses = relationship(Address, backref=user)


Jonathan,

  So I can specify the relationship from either class/table. I'll read the
docs again to make sure I fully understand which form to use when.

Thank you,

Rich

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Re: [sqlalchemy] Re: Foreign Keys and 'backref'

2014-07-31 Thread Rich Shepard 

On Thu, 31 Jul 2014, Jonathan Vanasco wrote:


The relevant docs say this (
http://docs.sqlalchemy.org/en/rel_0_9/orm/relationships.html#sqlalchemy.orm.relationship.params.backref
)


  Re-reading this section of the docs I'm seeing what I missed the first
time through.

Thanks again, Jonathan,

Rich

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Re: [sqlalchemy] Re: Foreign Keys and 'backref'

2014-07-31 Thread Jonathan Vanasco 
yes.  `backref` just lets you consolidate defining a relationship in a 
single place.

--

`relationship` lets you specify the relationship from A to B

`backref` is a kwarg to `relationship` that lets you specify the inverse ( 
B to A )

   class TableA():
b = relationship(TableB, backref=a)

   class TableB():
   pass

is the same thing as saying:

   class TableA():
b = relationship(TableB)

   class TableB():
a = relationship(TableA)

`backref` can either be a `String` OR a `backref()` constructor -- which 
lets you customized the join with the same conditions you can elect in the 
`relationship` constructor

   class Foo():
bar = relationship(Bar, lots_of_keywords_here=True, 
backref=backref(the_same_keywords_work_here=True) )

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Re: [sqlalchemy] Re: Foreign Keys and 'backref'

2014-07-31 Thread Rich Shepard 

On Thu, 31 Jul 2014, Jonathan Vanasco wrote:


yes.  `backref` just lets you consolidate defining a relationship in a
single place.



`relationship` lets you specify the relationship from A to B

`backref` is a kwarg to `relationship` that lets you specify the inverse (
B to A )

  class TableA():
   b = relationship(TableB, backref=a)

  class TableB():
  pass

is the same thing as saying:

  class TableA():
   b = relationship(TableB)

  class TableB():
   a = relationship(TableA)

`backref` can either be a `String` OR a `backref()` constructor -- which
lets you customized the join with the same conditions you can elect in the
`relationship` constructor

  class Foo():
   bar = relationship(Bar, lots_of_keywords_here=True,
backref=backref(the_same_keywords_work_here=True) )


Jonathan,

  That makes everything clear.

  My original confusion arose because I'm used to specifying many children
to one parent with the postgres syntax REFERENCES in the children's table;
that's the only relationships I've used (other than many-to-many in linking
tables). The abundance of options in SQLAlchemy threw me.

Much appreciated,

Rich

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