>From http://stackoverflow.com/q/10117143/937891

I'm trying to exclude posts which have a tag named meta from my selection, 
by:

meta_id = db(db.tags.name == "meta").select().first().id
not_meta = ~db.posts.tags.contains(meta_id)
posts=db(db.posts).select(not_meta)

But those posts still show up in my selection.

What is the right way to write that expression?

My tables look like:

db.define_table('tags',
    db.Field('name', 'string'),
    db.Field('desc', 'text', default="")
)

db.define_table('posts', 
    db.Field('title', 'string'),
    db.Field('message', 'text'),
    db.Field('tags', 'list:reference tags'),
    db.Field('time', 'datetime', default=datetime.utcnow())
)

*UPDATE:*

I just tried posts=db(not_meta).select() as suggested by @Anthony, but it 
gives me a Ticket with the following Traceback:

Traceback (most recent call last):
  File "E:\Programming\Python\web2py\gluon\restricted.py", line 205, in 
restricted
    exec ccode in environment
  File 
"E:/Programming/Python/web2py/applications/vote_up/controllers/default.py", 
line 391, in <module>
  File "E:\Programming\Python\web2py\gluon\globals.py", line 173, in <lambda>
    self._caller = lambda f: f()
  File 
"E:/Programming/Python/web2py/applications/vote_up/controllers/default.py", 
line 8, in index
    posts=db(not_meta).select()#orderby=settings.sel.posts, limitby=(0, 
settings.delta)
  File "E:\Programming\Python\web2py\gluon\dal.py", line 7578, in select
    return adapter.select(self.query,fields,attributes)
  File "E:\Programming\Python\web2py\gluon\dal.py", line 3752, in select
    (items, tablename, fields) = self.select_raw(query,fields,attributes)
  File "E:\Programming\Python\web2py\gluon\dal.py", line 3709, in select_raw
    filters = self.expand(query)
  File "E:\Programming\Python\web2py\gluon\dal.py", line 3589, in expand
    return expression.op(expression.first)
  File "E:\Programming\Python\web2py\gluon\dal.py", line 3678, in NOT
    raise SyntaxError, "Not suported %s" % first.op.__name__
SyntaxError: Not suported CONTAINS

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