How to do negative regex query using Java driver

[Temujin_12]

This is has sort-of been asked in different ways but I don't see any
satisfactory answer.

Let me see if I can explain it (using MongoDB 2.0.1 and java driver
2.6.5):

From console:
(yes, i know I don't have use extended $and syntax here, but bear with
me)
=========================================================
> db.test.find()
{ "_id" : ObjectId("4eb1863ada7081653c47bf38"), "id" : 1, "data" :
"foo" }
{ "_id" : ObjectId("4eb18642da7081653c47bf39"), "id" : 1, "data" :
"fooDup" }
> db.test.find({"$and": [{"data" : { $not : {$regex : '^foo$', $options : 'i'}}}, {"id" : 1}]})
error: {
"$err" : "can't use $not with $regex, use BSON regex type instead",
"code" : 13032
}
> db.test.find({"$and": [{"data" : { $not : !/^foo$/i}}, {"id" : 1}]})
error: { "$err" : "invalid use of $not", "code" : 13041 }
> db.test.find({"$and": [{"data" : /^foo$/i }, {"id" : 1}]})
{ "_id" : ObjectId("4eb1863ada7081653c47bf38"), "id" : 1, "data" :
"foo" }
> db.test.find({"$and": [{"data" : !/^foo$/i }, {"id" : 1}]})
=========================================================

Okay, I see that $not and regexes don't play well together.

However, in the Java driver, it appears that Pattern objects are
always sent using the extended $regex syntax (correct me if I'm
wrong).

Does this mean that there is no way to do *negative* regex queries
using the Java driver? Is there a bug or feature gap in the Java
driver.

And for the record, Java regex makes me frustrated. Why did they have
to go off and do their own thing?

[Scott Hernandez]

Do you have a working example from the javascript shell?

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[Temujin_12]

The example I posted above was from the javascript shell (I called it
"console").

What I'm having trouble doing is getting the Java driver to do a
negative regex query (does *NOT* match the regex ....).

[Temujin_12]

Put another way:

The Java API uses the Pattern java type. However, there is no way to
express a negative regex using the Pattern API (ie: !/^foo/i).

You can express the expanded $regex mongo condition by building it
yourself using a BasicDBObject, however there appears to be no way to
express a negative regex using the $regex mongo condition syntax.
Attempting to use the $not modifier causes the error shown above.

Since the Java driver seems to always use the expanded $regex syntax,
I don't see a way (using the Java driver) to do negative regex
queries.

Now that I read through the regex documentation more closely, I see
that there isn't an example using a negative regex.

Perhaps I should ask if Mongo's regular expressions support negative
expressions like:
* !/^abc/ - any string that does *NOT* begin with 'abc'
* !/.*abc$/ - any string that does *NOT* end with 'abc'

And if it does not, is there a way to express this otherwise?

[mdahlman]

Sure, you can do a negative regex. For example, this gets fields that
do not start with "a":

/^[^a]/

It works for me with the Java driver against a trivial data set.

-Matt

[Scott Hernandez]

On Fri, Nov 4, 2011 at 12:10 PM, Temujin_12 <caleb...@gmail.com> wrote:
> Put another way:
>
> The Java API uses the Pattern java type. However, there is no way to
> express a negative regex using the Pattern API (ie: !/^foo/i).
>
> You can express the expanded $regex mongo condition by building it
> yourself using a BasicDBObject, however there appears to be no way to
> express a negative regex using the $regex mongo condition syntax.
> Attempting to use the $not modifier causes the error shown above.
>
> Since the Java driver seems to always use the expanded $regex syntax,
> I don't see a way (using the Java driver) to do negative regex
> queries.

This is incorrect, it does not use that form. It just prints that so
it is more readable from toString.

[Temujin_12]

Ok, that makes sense.

I think that I am also mistaken about the leading '!' (eg: !/^abc/). I
believe that is not PCRE compliant and that one cannot use the same
regex and apply a meta-level negative flag or modifier.

As you pointed out, it looks like one must use negative look behinds
or look aheads to express this kind of negative.

I believe that I got my misinformation from PCRE tables used in
postfix (which allow that !/^abc/ syntax). See http://www.postfix.org/pcre_table.5.html.

Thanks for setting me straight.

:-)

On Nov 4, 9:44 am, Scott Hernandez <scotthernan...@gmail.com> wrote:

[Temujin_12]

BTW, is there any reason why not to allow $not with regular
expressions?

On Nov 4, 9:56 am, Temujin_12 <calebjo...@gmail.com> wrote:
> Ok, that makes sense.
>
> I think that I am also mistaken about the leading '!' (eg: !/^abc/). I
> believe that is not PCRE compliant and that one cannot use the same
> regex and apply a meta-level negative flag or modifier.
>
> As you pointed out, it looks like one must use negative look behinds
> or look aheads to express this kind of negative.
>
> I believe that I got my misinformation from PCRE tables used in

> postfix (which allow that !/^abc/ syntax). Seehttp://www.postfix.org/pcre_table.5.html.