On May 27, 2013, at 5:12 PM, Chris Withers <[email protected]> wrote:
> Hi,
>
> I'd like to come up with a string column type that prevents empty values, or
> a function that returns a string column which prevents empty values.
>
> I've tried two approaches, both of which failed:
>
> class NotEmptyString(String, SchemaType):
>
> def _set_table(self, column, table):
> table.append_constraint(CheckConstraint(column != ''))
>
> The above works, but results in two check constraints for each NotEmptyString
> on each table, why is that?
I'm not able to reproduce that, only does it once for me (I'd pdb to see if
_set_table() is being called multiple times).
You can avoid the underscore method using events though a little more verbosely:
class NotEmptyString(String, SchemaType):
def __init__(self, length, **kw):
String.__init__(self, length)
SchemaType.__init__(self, **kw)
from sqlalchemy import event
@event.listens_for(NotEmptyString, "after_parent_attach")
def _set_column(type_, column, **kw):
@event.listens_for(column, "after_parent_attach")
def _set_table(column, table, **kw):
table.append_constraint(CheckConstraint(column != ''))
>
> def not_empty_string(size, **kw):
> col = Column(String(size), nullable=False, **kw)
> cons = CheckConstraint(col!='')
> cons._set_parent_with_dispatch(col)
> return col
>
> So, I tried this to get around the two-check-constraints problem, but here
> the issue is that I don't have the column name when I need to make the
> constraint, the above barfs when creating the table:
>
> ProgrammingError: (ProgrammingError) syntax error at or near ":"
> LINE 3: id VARCHAR(10) NOT NULL CHECK (table.col != :param_1),
>
> What should I have been doing here and what am I doing wrong?
>
> In the meantime, I'll just use table-level check constraints, but I'd like to
> make this DRY and I don't want to risk forgetting the constraint for a
> column...
>
> cheers,
>
> Chris
>
> --
> Simplistix - Content Management, Batch Processing & Python Consulting
> - http://www.simplistix.co.uk
>
> --
> You received this message because you are subscribed to the Google Groups
> "sqlalchemy" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to [email protected].
> To post to this group, send email to [email protected].
> Visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
> For more options, visit https://groups.google.com/groups/opt_out.
>
>
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
For more options, visit https://groups.google.com/groups/opt_out.
