So let's take a look at what it looks like when it's pretty so we can see it easier.

So you notice that we have the name, published date, authors, and the id. We have all of these different elements and that is fine in some cases, however, if you remember back when you were learning about SQL, if you have learned about SQL then you would remember that running a star query where you bring back all of the attributes, that's actually considered a poor practice. So in Mongo, it's the same thing. It's fine to run it at certain times however it's pretty rare that you want every single one of the attributes usually you want to pick and choose what gets returned back. And so that takes us into the conversation where we learn about what are called projections and so projections are various constraints that we can put on our query so that we can ensure that we're only getting back the elements that we actually want. So let's open up Sublime Text and let's create a new query with projections. So I'm going to say db followed by the collection that we want to find and then find, inside of find where we're going to place a couple of different arguments. So what find allows us to do is not only pass in what we've done so far which is pass and a single object. It also allows us to pass in our second object which is our projection. Here I'm going to pass in one object and this is going to be similar to what we've done so far, I can a name and then Confident Ruby and also notice that we have a couple of different syntax options. There are times where I will wrap this up just like this in a string. But if you just say name just like I'm doing right here then Mongo is still going to be able to interpret that. So this is what we've done so far and if I copy this

and come in the terminal and run it you can see that it brings back the correct book. However, it brings back all the attributes.

So now what we can do is pass in a second object and in the second object, this is where all of our projections go, our constraints that allow us to say that we only want certain attributes. The way that we can do this is by naming the attributes that we want. So if I say publishedDate and then the way that you tell it if you want it or not is with either a 1 or 0. In this case, I want the publishedDate and I want the authors.

So now if I run this and run this in the terminal now you can see and let me make it so it's pretty as well. Now you can see that it's actually working and that we only got back the id the publishedDate and the list of authors.

Now if we wanted the name then we could add that right to the list and here I will add my pretty statement right to the end, and now if I pass this and again you can see it's working and now we have the name back.

Now let's see what happens when we want to not have some of those elements. So say I just want the name and the list of authors but not the publishedDate. So if I copy all of this and run it. Notice that the published date is not there anymore.

You may think that you'd have to place a zero by the published date but that's not true because the way that Mongo works is it is expected that if you want the value then in that list of projections you're going to ask for it. The only one that you do not have that's not the expected result is that id field. So if you do not want the id field then you can pass in a zero just like this and now if I run this you can see and it looks like I have a little syntax error and I do I need to add a comma. Remember this is an object so you have to pass it in and have a comma after each one of the items in the list.
Now let me clear this off and run it again and you can see that now we have run it and it does not have the id field anymore.

The id field is the only one that comes by default in your projections. You simply have to list out with either a 1 or a 0 which one of the attributes that you want to return. So the way that this would be in SQL so this command right here would be the same as if we did something like

SELECT name, authors FROM books WHERE name = 'Confident Ruby'

So this is something that when I was learning Mongo it really helped me to be able to see that mapping because even though Mongo may be incredibly different from SQL at the end of the day your end goal is the same. You need to be able to insert items into a database and then you need to be able to retrieve them. Typically you need to be able to retrieve only certain components that you want back and you want to be able to also pass in clauses for being able to say that I don't want you to return all the documents back. I only want the ones that match these certain values. So being able to have an understanding of how similar SQL would be helped me quite a bit so hopefully, it also helps you. So in review what we've worked through here is being able to limit the amount of data that comes back in a query by adding that second object into the find method which is called your set of projections.

Code

db.books.find(
  {
    name: "Confident Ruby"
  },
  {
    _id: 0,
    name: 1,
    authors: 1
  }
).pretty()

SQL Equivalent

SELECT name, authors FROM books WHERE name = 'Confident Ruby'