3. GraphQL arguments

Querying for a specific track

We've updated our schema with new and the Module type, but we still need a way to for a specific track by its ID. To do that, we'll need to add another entry point to our schema.

In our schema.js file in the server/src folder, we can see that we only have a single entry point to our API so far: the tracksForHome that returns a list of Track objects. Let's add another one called track, which will return a single Track.

Add the following to our schema's Query type:

track: Track
Where can we add entry points to our schema?

We'll be able to specify which unique track we're for by giving this an argument.

🤔 How to use GraphQL arguments

An is a value you provide for a particular in your . The schema defines the arguments that each of your fields accepts.

Your can then use a 's provided to help determine how to populate the data for that field. Arguments can help you retrieve specific objects, filter through a set of objects, or even transform the field's returned value. A that performs a search usually provides the user's search term as an argument.

Doodle of resolver function retrieving a specific object from data-land using an argument

To define an for a in our schema, we add parentheses after the field name. Inside, we write the name of the argument followed by a colon, then the type of that argument, like String or Int. If we have more than one , we can separate them with commas.

Illustration showing the syntax breakdown of using GraphQL arguments
Which of these are reasons to use arguments in a query?

🙌 Using arguments

In our case, we want to use the track's ID as our . Following the syntax rules, we'll add the parentheses, then the name id, with the type ID which is required.

Inside the Query type in schema.js, update the track to:

"Fetch a specific track, provided a track's ID"
track(id: ID!): Track
Code Challenge!

Update the schema below to add two new entry points: 1) Query for a specific spacecat. This field takes an argument id of type non-nullable ID and returns a nullable SpaceCat. 2) Query for a list of missions. This field takes two arguments: to of nullable type String (to specify the mission destination), and scheduled of nullable type Boolean (to filter for scheduled or unscheduled missions). This field returns a nullable array of nullable Missions.

That's it for the definition. We now have our schema up-to-date for the feature we're implementing. Onwards to the !


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