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So time to practice what we did.

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For this, I'll first of all,

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fetch all my restaurants again

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and now I wanna leave a review for the Berlin Burgerhouse.

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For this, I'll again repeat this insert one command.

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I pressed the up key to get to this command again here.

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And now this time, it's not for the Munich Schnitzelhouse.

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Instead, it will be for this Berlin Burgerhouse.

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So I'll copy that name, copy that string here, this ID,

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and replace this ID and object ID with it.

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And I'll leave the date for convenience reasons,

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change the review text a little bit though.

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This was amazing.

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And change the rating here to five,

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and I will leave my name.

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And actually here, I was lacking a closing parenthesis

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so now I insert this and now this review was also inserted.

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So now we got two reviews,

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if we find that we got two

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restaurants and of course we could add more,

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but now I want to instead practice querying.

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And let's say we want to find all the reviews

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that have a rating greater than four.

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In this case, that would only be one review.

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To do this,

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we can execute db reviews find,

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and then pass our condition here.

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And you'll learn that here, for example,

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we can look for reviews that have a rating of five

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like this,

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but we can also do things like searching for values

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greater than four or a smaller than three

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or whatever you want to do.

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For this, instead of passing a value here,

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you pass an object and then you use the special dollar sign

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gt or lt commands here.

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There also is lte and gte,

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which stands for a greater than or equal

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or just greater than, or lower than or lower than and equal.

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So these again are reserved names,

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reserved filter conditions that you can use when filtering.

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It's important that you pass them inside of an object,

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which you pass as a value for the key where you want

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to filter.

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And then for example,

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you can search for reviews where the rating is greater

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than four by running this command.

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And of course,

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we only find one review here because the other review

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had a rating of three, which is not bigger than four.

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Now you can find a list of all these supported operators

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in the official Mongo DB documentation.

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If you search for query and projection operators,

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or you click into reference operators,

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query and projection operators,

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here you find comparison operators like gt,

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which I just showed you.

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And there are more operators,

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also for concatenating conditions and so on.

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Again, I got a full Mongo DB course where you can learn

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all about that in great depth,

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but the official docs here of course are also a great place

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to play around with that and practice these things.

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For example,

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if you would want to find all reviews that are greater

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than four and smaller than three,

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you could write this differently and write dollar sign and,

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and then a list of all the conditions that should be met.

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That's what you'll learn in the official documentation here.

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And then in there in this list, you have objects.

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So opening and closing curly braces,

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where you look for a rating gt one

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and then separated by a comma another object

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where you look for rating lt three.

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So I guess we're looking for ratings

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with a value of two here,

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but I just want to show you how you could,

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for example, also combine conditions.

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And here, of course,

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I don't find anything because we have no review

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with a rating of two in this case.

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Now this might look strange at first.

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I just want to show you how this looks like.

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And it is actually a syntax that will quickly

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become familiar the more you work with it.

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Again, the official docs or dedicated courses

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are great places to dive deeper into that.

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But of course,

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we're also going to work with Mongo DB

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and also run different kinds of queries,

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again throughout this course, for example,

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in the next course section.

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So that's how we can query data and how we can insert data.

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Now let's also quickly, again,

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practice updating and deleting data.

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And for this,

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I'll come back to my restaurants and find all my restaurants

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here.

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And let's see here.

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I actually do want to update the address

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of my Munich Schnitzelhouse again.

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Now of course,

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also feel free to practice this on your own.

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We did already make such update a couple of lectures

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ago already.

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Now I will grab this ID here.

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Actually,

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we can grab this entire code snippet here to identify

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this restaurant by this ID and then to update it,

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we can run update one because I only want to update

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the first matching document and look for the document

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where the ID is equal to this object ID.

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And then we pass a second argument,

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a second parameter value to update one.

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And here you now use the special dollar sign set key,

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which is understood by Mongo DB.

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And another pair of curly braces.

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So you work a lot of curly braces when working with

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Mongo DB, as you can see.

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And then here we point at our nested field

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by using address dot street between quotes, like this.

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And then the value you want to set here,

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let's say schnitzel street.

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And this is how we could update the street field

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in the nested address document in the restaurant

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with this ID.

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Hit enter.

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You'll see one document was modified.

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And if we now, again, simply find all restaurants,

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here we have the new street.

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Now last, but not least,

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we can of course also delete documents.

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And for example, delete a review.

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For this, I'll quickly find all of them again.

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And let's say, I want to delete to this first review.

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Well, then we can just grab that ID to identify it

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by that ID.

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And then run db reviews delete one.

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And between curly braces search for the ID,

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which has this object ID and hit enter.

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And now this was deleted. And of course, therefore,

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if we try to find all the reviews,

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this review is now missing.

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So these are the CRUD operations we can run with Mongo DB.

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That's the general base syntax you should understand.

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Again, we'll see more examples throughout this course.

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And most importantly,

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you now should understand what the idea is behind

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storing data in a NoSQL database.

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That we don't work with dozens of tables,

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but that we instead try to plan for the queries

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we're about to run and that we then store relate data

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together.

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Not all the time.

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As you saw with restaurants and reviews,

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where we still had two collections, but often as you,

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for example,

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saw with restaurants and the addresses

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of these restaurants.