[Sqlalchemy-tickets] Issue #3243: ForeignKeyConstraint.columns - WAT (zzzeek/sqlalchemy)

[Mike B. <iss...@bi...>]

New issue 3243: ForeignKeyConstraint.columns - WAT
https://bitbucket.org/zzzeek/sqlalchemy/issue/3243/foreignkeyconstraintcolumns-wat

Mike Bayer:

The ".columns" collection is first off not a ColumnCollection, and secondly it is a list that is either of strings or columns, depending on factors that are in a practical sense arbitrary, which is ridiculous.   This collection should either not be there at all, or just changed to be a ColumnCollection.   Hitting it will just invoke the FK.  Some other accessor should be added that gives us the column names in the absense of the FK constraint actually being set up.

```
#!python

from sqlalchemy import Integer, Column, Table, MetaData, \
    ForeignKeyConstraint, ForeignKey

m = MetaData()

t1 = Table(
    't1', m,
    Column('x', Integer, primary_key=True)
)

t2 = Table(
    't2', m,
    Column('y', Integer, primary_key=True),
    Column('z1', Integer, ForeignKey('t1.x')),
    Column('z2', Integer)
)

fk1 = [
    const for const in t2.constraints
    if isinstance(const, ForeignKeyConstraint)][0]
fk2 = ForeignKeyConstraint(['z2'], ['t1.x'])

# keys are Column objects, OK
assert isinstance(fk1.columns[0], Column)

# WAT
assert isinstance(fk2.columns[0], str)
t2.append_constraint(fk2)

# WAT
assert isinstance(fk2.columns[0], str)


```