Check if a document's value is in an array MongoDB

Question

I have ~ 200,000 documents in a collection which look like this:

{
 "_id": "tdhABqSZPEZ2fFcEzOVCb-q8d",
 "user": "testuser",
 "content": "Test Content"
}

And I have an array with ~50,000 entries:

let arr = ["tree", "apple", "test", "orange", ...otherEntries] // ~ 50,000 entries

I want to get all documents where any element of the array is in the content value, non case-sensitive, so that the example document above would be returned because in the array is test and in the content of the document is Test.

This would work using $where and then using a JavaScript expression but this is not very fast. Is there a really fast way (< 1-2 seconds) of doing a query like this or do you have any idea on how to restructure the documents that I can perform a fast query like this?

why don't you use docs.mongodb.com/manual/text-search its creating the index. So highly recommended than normal find() — varman
– varman, Commented Aug 21, 2021 at 7:45
Because I want to input an array to check if any array element is in the text and I couldn't find anything like that in Text Search — Xge
– Xge, Commented Aug 21, 2021 at 7:49
Yeah, it is, but I don't know how I would do that. Can you answer this question with this solution so I can see if it works for me? — Xge
– Xge, Commented Aug 21, 2021 at 11:49

Takis · Accepted Answer · 2021-08-21 14:38:28Z

3

If you list(arr) was small => you could use make one index and use $in and filter (but its not small)
if you wanted case sensitive => you could make the list to a collection and $lookup with indexes (but you want case insensitive)

In you case that you have big list, and you want case insesitive

join the list into a big string(lets name it MyListString its a variable in your driver), separated with spaces for example ["hat" "tree"] to become "hat tree"
create a text index on content its very easy to do for example in Java i did mycoll.createIndex(Indexes.text("content")); see your driver documentation on how to create text indexes.
Do a find or an aggregation with match (MyListString is the above big string variable) (this does by default a case insensitive match)

{ "$match" { "$text" { "$search" MyListString} } }

Time was < 1 sec in my benchmark, test it, i think you will be fine.

answered Aug 21, 2021 at 14:38

Takis

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3 Comments

Xge Over a year ago

Thank you for that answer! That's what I've tried a few hours ago but unfortunately my problem now are two things: 1. In this large array of strings are strings with spaces. So ["abc", "def ghi", "jkl"] would become "abc def ghi jkl". So I would need to map the whole array so every string would become e. g. "\"def ghi\"" - I don't know how to do this in a fast way for such a big array. 2. I have 10 of these large arrays and I want to make only one query. Is that possible? Tried it with $facet but when using $match and $text in $facet, it throws an error since this is impossible I guess

Xge Over a year ago

But in fact this is the solution to my described problem

Takis Over a year ago

Making that big string in the driver(for example in Javascript) is very fast.Now if you have more arrays you can make 1 array with the contents of all arrays and 1 string again, it will be very fast also.I am not sure i understanded the problem. If you are stuck or query is slow maybe ask new question.

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