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Let's now jump back to the user database and in there, just a quick reminder we got that user data.

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Now let's say we want to find all users who have a hobby of sports and the frequency should be equal

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to two,

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so the frequency of the sports hobby.

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Let's try this, let's reach out to our users and we want to find all users where this is true,

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now how could this query look like?

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Well we could use the and keyword and then we have multiple conditions and the first condition is that

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for hobbies, whoops, for hobbies.title, we're looking for sports,

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right this was the first part,

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it should be sports.

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The second condition could be that hobbies.frequency should be equal to 2

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and that also has to be wrapped in curly braces

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or let's say it should actually be greater than or equal to 2.

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If I hit enter,

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yeah find Anna, make sense,

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she has sports and frequency two

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and I find the whole document of course because find always gives me the whole document even if I'm

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just digging in some array or embedded document,

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it doesn't return the embedded document but always the full document which contains the embedded document.

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So I find Anna because she has sports title two, frequency two, I also find Max because there, I got sports frequency

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three.

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Now let's say I repeat that query and modify it slightly

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and now I'm looking for a frequency greater than or equal to three,

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now what's that?

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I still find Anna even though for her sports hobby, the frequency is two

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but our query was that the frequency should be greater than or equal to three,

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so what's going wrong here?

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The thing is with this query, we're basically saying find me all documents where in hobbies,

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there is a document at least one document with the title sports and a document with the frequency greater

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than or equal to three,

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it does not have to be the same document,

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that is our issue here

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and indeed for Anna, yoga has a frequency greater than or equal to three.

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She has a sports element

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so the first part is satisfied and the second part is satisfied with that other element.

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Now of course it's not that uncommon that you want to ensure that one and the same element should match

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your conditions

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and for that, you have the elemMatch operator. So this query

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and I'll just count it so that we have it still on page, this query can be replaced with another query

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that should do what we want. Instead of and,

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we specify our array hobbies and then a value which is a document where we use $elemMatch,

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that

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then again takes a document as a value

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and here, we then describe how to match our element.

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Now if hobbies were just an array of numbers let's say, you could immediately start typing greater than

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30 but lower than 50 for example,

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so that would be the case if hobbies would really just be an array of numbers,

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not of embedded documents.

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However here, we have embedded documents and in this case, $elemMatch is a document where you now describe

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what to look for inside of the embedded document,

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so here we're saying title should be sports and the frequency should be

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and now here we can still write our old condition gte three.

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So this is how we can now use $elemMatch on an array with embedded documents,

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we essentially you could say describe how a single document should look like to match our query and

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if it finds at least one document in the hobbies array that has a title sports and a frequency greater

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than or equal than three,

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it will include the overall document that contains that hobbies array in the result set.

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If we got multiple elements in the hobbies array fulfilling this criteria, that would also be fine.

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And if I now hit enter, I only find Max and not Anna anymore because Max is the only user who has a

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hobby with a title of sports and a frequency of three.