Does mongo regex query have character limit, if the regex search string is more than that limit it throws error

Question

I am seeing mongo regex query not returning result when the regex searched string is very big, instead its throwing error. I have a scenario where I append lot of names to do a regex and thus my regex search string goes beyond 40000 characters. eg:

db.getCollection('collection').find(
    {"name":{"$regex" :"name1 | name2 | name3", "$options":"-i"}}
)

Answer 1

Can you explain why you are doing this? The idea of a regex is to create a expression with which you match (multiple) value(s).

example expression:

name\d+

will match on all "namex" vales where x is a decimal.

The idea will be to create a single expression to fullfill your query requirement.

When you want to match on multiple string values you can use $and operator

Answer 2

Yes, mongoDB regex has character limit, originates from perl regex limit. Because "MongoDB uses Perl compatible regular expressions (i.e. “PCRE” ) version 8.41 with UTF-8 support."MongoDB v3.2

You can see the limitation is 32764 characters:MongoDB add assert of regular expression length

I recently met this issue, and the solution was to use $in query operator instead. $in does not have characters limit. This suits my problem, since it was exact match rather than pattern matching in such long input case.