MongoDB reverse regex

Question

I have a document in MongoDB with a regex attribute

    {
        _id: ObjectId("516023189732da20ce000004"),
        regex: /^(my|your)\s+regex$/
    }

and I need to retrieve this document with something like db.col.find({regex: 'your regex'}) and db.col.find({regex: 'my regex'}). In MySQL I'd do: SELECT * FROM table WHERE 'my regex' REGEXP table.regex. How can I achieve this in MongoDB?

hnmm maybe I am missing something but doesn't: db.col.find({regex: '/^[my|your]\s+regex$/'}) work since it isn't outisde of quotes and it isn't a regexp object? — Sammaye
– Sammaye, Commented Apr 12, 2013 at 9:01
This seems to be a perl(ish) regex. This means this will not match to my regex or your regex, but m regex or y regex or | regex &c. If it had to match with my regex it would be /^(my|your)\s+regex$/. Am I missing something? — TrueY
– TrueY, Commented Apr 12, 2013 at 9:11
@Sammaye I need to match a string against a regex object attribute. — Giovanni Lovato
– Giovanni Lovato, Commented Apr 12, 2013 at 9:21

fgalan · Accepted Answer · 2013-04-13 15:36:32Z

11

You can use the $where operator in the following fashion:

db.col.find({$where: "\"my regex\".match(this.regex)"})

answered Apr 13, 2013 at 15:36

fgalan

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3 Comments

Giovanni Lovato Over a year ago

Although pretty slow, it works, thank you! But it matches also documents where this.regex is not defined, so I think I'm going to define a function instead of the expression.

fgalan Over a year ago

I'm afraid that using $where is always slow, MongoDB documentation discourages using it... I also would like to know about quicker ways :) Of course, you can use a JavaScript function for the $where value to deal with edge cases such as not defined fields, etc.

fgalan Over a year ago

BTW a ticket is opened in MongoDB JIRA about this improvement jira.mongodb.org/browse/SERVER-13902

J.F. · Accepted Answer · 2021-11-15 19:07:37Z

7

As explained into Jira ticket provided by @fgalan on 2013, you can use $expr you can use this query:

db.collection.find({
  "$expr": {
    "$regexMatch": {
      "input": "$key",
      "regex": "$regex",
      "options": "i"
    }
  }
})

Example here

With $expr you can avoid $where which is not efficient.

answered Nov 15, 2021 at 19:07

J.F.

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1 Comment

Jonatas Dec 9, 2024 at 21:53

Is there any kind of index to satisfy and speed up this query?

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