GraphQL Tutorial #9 - The Resolve Function

all right and so where are we up to well in the last video we created this Rick query right here and remember we said the requiring defines how we can jump into the graph to query data so imagine something on the front end some kind of application makes this requiring they say ok we're making a query for a book with an ID of 2 and we want these two fields the name and genre so when that query gets to our graph QL server it's going to look at it and say ok this requiere is a book query so I'm going to find that query inside our root query object type inside the fields and I find it right here and it looks inside that book field to know how to deal with this query and it says ok well I know what object type I'm dealing with now it's a book type also it looks at the arts property and says right well I'm expecting an ID to come along with this query do we have one yes we do is right here it's an ID of 2 so it takes this idea and it attaches it to this rx parameter right here so the inside the resolve function we have access to it so when we get this query it's going to fire up this resolve function and in here is where we're going to write the code to find that book now this book and this data could be stored in a no sequel database or a sequel database it doesn't really matter where it's stored we're gonna write some code here to go and grab it later on we'll be using MongoDB to store all of our data but for now I think what I'll do is just create an array to store some books in inside this feet file so underneath here let's just write a comment saying dummy data and then underneath I'm just gonna paste this in so don't want you to watch me doing it it's just a waste of your time so we have a book serrate right here and it's just basically some dummy data to store temporarily like I said later we'll be using MongoDB but we have three different book objects inside and each one of them have a name as Janvrin and an ID so this is the ID we're going to use to find the correct book so if a query comes in for the book ID of two we to get the book of ID 2 from this array right here or from a database later on so now it's our job inside this resolved function to take the ID from the args parameter right here an ID of 2 or whatever ID comes in and we're going to look at this array to find the book with that ID now I could do that with vanilla JavaScript but I'm going to make life easy for myself and install a utility module called lodash so I'll say npm install lodash to do that and what LO - is gonna allow us to do is a load of different tricks to find data or change data inside of this array plus lots of other things as well it's a really cool library so I'm going to say const underscore is equal to require low - alright then so down here we can use low - to look at this array and find the book with whatever ID has been attached to this args property so underneath this comment let's just say underscore dot find then we want to search through the books array and we need a second parameter which is going to determine how we're finding a particular book so the second parameter is going to be an ID property which is gonna be args ID all right so now when this query comes in we're gonna fire this resolve function we're gonna use lodash to look through the books array and we're going to return or find any book that has an ID equal to the ID that's been attached to the odds right here that the user sends along so in this case it's gonna look for a book with an ID of two and it's gonna give us that alright so what we need to do is return this value which comes back from this thing right here ok whatever we're sending back to the user we're gonna return so now when they make this request ultimately what's going to happen is they're gonna get that book returned to them all right so that is how we use the resolve function to find the data like say later on we'll be using a proper database rather than just this array up here but now we've done that we're kind of created nearly a full enough schema to work so in the next tutorial what we'll do is we'll test this out in graphical that tool that dummy tool on the front end that we can use to test different queries so make sure you delete this before you save anything and then I'll see you in the next video