mongo query regex inside a list

Question

I have a collection that contains a list field. The list field contains URLs. I want to search that field and pull out all documents where that pattern appears in at least one element in the list. This is one of my first attempts.

query = collection.find({
'third_party_urls' : {'$in' : ['/.woff/']}
})

This returns zero documents, but I know the condition is true in many cases. MongoDB's documentation states that I can't use the $regex operator in a list, but I can use js object regex. According to MongoDB and a quick google search about js regex, I write a pattern encapsulated in / /. So I am confident that I'm using js regex correctly, but no luck. Any ideas?

MongoDB implicitly performs array element matches, you do not need $in for that and $in in MQL has different meaning from SQL IN. — D. SM
– D. SM, Commented Jun 26, 2020 at 21:38

fishstick · Accepted Answer · 2020-06-26 23:39:07Z

2

Say we have a collection named so. We insert several documents using following commands in mongo shell:

db.so.insert({urls: ["apple", "banana"]})
db.so.insert({urls: ["apple2", "banana2"]})
db.so.insert({urls: ["apple3", "banana3", "cherry"]})
db.so.insert({urls: ["mongo"]})

Then we can find all documents that has at least one element that begins with apple by issuing:

db.so.find({urls: /^apple.*/})

OR

db.so.find({urls: {$regex: "^apple.*"}})

The result is something like below:

{ "_id" : ObjectId("5ef6829b25a20c5a694d8522"), "urls" : [ "apple", "banana" ] }
{ "_id" : ObjectId("5ef682a525a20c5a694d8523"), "urls" : [ "apple2", "banana2" ] }
{ "_id" : ObjectId("5ef682d425a20c5a694d8524"), "urls" : [ "apple3", "banana3", "cherry" ] }

edited Jun 26, 2020 at 23:39

answered Jun 26, 2020 at 23:28

fishstick

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1 Comment

unltd_J Over a year ago

The $regex answer worked, the other didn't. Interesting, because Mongo says you can't use the $regex operator inside a list.

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