156

I am trying to perform a regex query using PyMongo against a MongoDB server. The document structure is as follows

{
  "files": [
    "File 1",
    "File 2",
    "File 3",
    "File 4"
  ],
  "rootFolder": "/Location/Of/Files"
}

I want to get all the files that match the pattern *File. I tried doing this as such

db.collectionName.find({'files':'/^File/'})

Yet I get nothing back. Am I missing something, because according to the MongoDB docs this should be possible? If I perform the query in the Mongo console it works fine, does this mean the API doesn't support it or am I just using it incorrectly?

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4 Answers 4

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216

If you want to include regular expression options (such as ignore case), try this:

import re
regx = re.compile("^foo", re.IGNORECASE)
db.users.find_one({"files": regx})
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3 Comments

Note also that regex's anchored at the start (ie: starting with ^) are able to use indexes in the db, and will run much faster in that case.
Regex's starting with ^ can only use an index in certain cases. When using re.IGNORECASE I believe mongo can't use an index to perform the query.
Is this usage documented somewhere? I can't find this in the official pymongo API doc.
185

Turns out regex searches are done a little differently in pymongo but is just as easy.

Regex is done as follows :

db.collectionname.find({'files':{'$regex':'^File'}})

This will match all documents that have a files property that has a item within that starts with File

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8 Comments

Actually, what you have here is also the way it's done in javascript (and probably other languages too) if you use $regex. @Eric's answer is the python way that's a little different.
what's the difference? They're both using python pymongo correct? It is part of mongodb queries so I don't see the issue really.
Ignorecase is possible in regex of mongodb JScript also viz. db.collectionname.find({'files':{'$regex':'^File','$options':'i'}})
This answer looks better to my eyes. Why bother compiling a Python RE if you're just going to stringify it so that Mongo can compile it again? Mongo's $regex operator takes an $options argument.
Please use r'^File' instead of '^File' to avoid other problem
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18

To avoid the double compilation you can use the bson regex wrapper that comes with PyMongo:

>>> regx = bson.regex.Regex('^foo')
>>> db.users.find_one({"files": regx})

Regex just stores the string without trying to compile it, so find_one can then detect the argument as a 'Regex' type and form the appropriate Mongo query.

I feel this way is slightly more Pythonic than the other top answer, e.g.:

>>> db.collectionname.find({'files':{'$regex':'^File'}})

It's worth reading up on the bson Regex documentation if you plan to use regex queries because there are some caveats.

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1 Comment

If you need to match agains an array using $in then $regex would not work for you. bson.regex.Regex will do the trick!
10

The solution of re doesn't use the index at all. You should use commands like:

db.collectionname.find({'files':{'$regex':'^File'}})

( I cannot comment below their replies, so I reply here )

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