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Let's now come to evaluation

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operators. Now json schema is something I covered in the document schema module,

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you could also use it in a query to find elements that have a certain document schema,

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so you set up a schema there as a value just as shown for validation. Mod is the modulus operator,

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so here you could basically divide a field value with a certain number and then check if the result

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is ok for you. Text is something

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I'll come back later in the indexes module where it's deprecated and basically replaced with expression,

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so in the next lectures we'll have a look at expression and regex

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and let's start with regex.

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Regex allows you to search for text and for that, I'll switch back to my movie data database

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and run some query on my movies,

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remember if we quickly find one, there we also have a summary field.

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Now let's say we want to search for a text snippet in there, we want to search for a musical just because

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I see it here.

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Now what we could of course think that it will work is that

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we access our movies and then we find all movies where summary, that was the field name is equal to musical.

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But if I do it like this, I find no entries because this looks for full equality,

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so it would find all documents where summary is exactly equal to musical, written like this. Well musical

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is just one word in there though and not the complete entry,

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so this does not work.

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Now for finding text snippets, the most efficient way of doing it is to use a text index, something you

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will learn about in the indexing module

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but if you don't have such an index, you can't use one or you only have very short text snippets which summary

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is already a bit above to be honest

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but let's still use it, then you can use regex query but be aware that it will not be super performant.

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So what you could do here is you can specify $regex and regex stands for regular expression

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which is a way of searching text for certain patterns. Now you can dive deeper into regex, setting

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up these patterns can be quite complex,

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we'll keep it simple here,

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a pattern is always surrounded by forward slashes and in-between you define your pattern. The simplest pattern

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possible

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is that you just type a word

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and now this will not look for full equality but it will look for this word in all the summaries and

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return all documents where in the summary, this word can be found.

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So if I now hit enter,

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now we find this item here where we see musical here

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and note that it's a different item than we saw before because if I scroll up,

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then here we have that musical comedy we saw earlier.

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So this is regex, nice for searching text but not the most efficient way of doing that,

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hence definitely have a look at the text index in the indexes module.

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Now that was regex,

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now what does expression do?