negation of labeled element?

[Mike Bayer]

this is technically something that semantically doesn't make sense, but in the "what I expect" category it does, which is to negate the inner element of a label.

from sqlalchemy import *

expr = or_(column('x') == 1, column('y') == 2)

bug = not_(expr.label('foo'))

from sqlalchemy.dialects import sqlite

print bug.compile()
print bug.compile(dialect=sqlite.dialect())

#!


NOT x = :x_1 OR y = :y_1
x = ? OR y = ? = 0

so the parenthesis are lost because we don't unwrap the label(), and we in fact hit a rule in ColumnElement._negate() where it assumes we're negating a true/false, so for a non-native-boolean it then sticks on "= 0" to the whole thing to make things worse.

[Mike Bayer]

Add _negate() to Label to negate inner element

Fixed the negation of a :class:.Label construct so that the inner element is negated correctly, when the :func:.not_ modifier is applied to the labeled expression.

Change-Id: Ia99917b2959bdfbff28689c962b4203911c57b85 Fixes: #3969

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