tometadata() doubles up unique constraint for unique=True #3721
Description
Migrated issue, originally created by Michael Bayer (@zzzeek)
from sqlalchemy import Table, MetaData, Column, Integer
m1 = MetaData()
t1 = Table(
't', m1, Column('id', Integer, unique=True)
)
m2 = MetaData()
t2 = t1.tometadata(m2)
print t2.constraints
output:
set([UniqueConstraint(Column('id', Integer(), table=<t>)), PrimaryKeyConstraint(), UniqueConstraint(Column('id', Integer(), table=<t>))])