GraphQL arguments - GraphQL Tutorials

Lift-off III: Arguments

Feature Overview Updating our schema GraphQL arguments Resolver args parameter Resolver chains Query building in Apollo Sandbox Building the track page The useQuery hook - with variables Navigating to the track page

3. GraphQL arguments

3m

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❓ Querying for a specific track

We've updated our schema with new fields and the Module type, but we still need a way to query 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 field that returns a list of Track objects. Let's add another one called track, which will return a single Track.

Add the following field to our schema's Query type:

track: Track

Where can we add entry points to our schema?

In any object type (Track, Module, etc.)In the Query typeIn our resolversIn the EntryPoint type

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

🤔 How to use GraphQL arguments

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

Your resolvers can then use a field's provided arguments 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 query 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 argument for a field 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 argument, 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?

To filter a set of objectsTo retrieve a specific objectTo transform a field's returned valueTo provide a user-submitted search term

🙌 Using arguments

In our case, we want to use the track's ID as our argument. 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 field 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.

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Loading initial values

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

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fields

A unit of data that belongs to a type in a schema. Every GraphQL query requests one or more fields.

type Author {
  # id, firstName, and lastName are all fields of the Author type
  id: Int!
  firstName: String
  lastName: String
}

query

A request for specific data from a GraphQL server. Clients define the structure of the response, enabling precise and efficient data retrieval.

field

A unit of data that belongs to a type in a schema. Every GraphQL query requests one or more fields.

type Author {
  # id, firstName, and lastName are all fields of the Author type
  id: Int!
  firstName: String
  lastName: String
}

field

A unit of data that belongs to a type in a schema. Every GraphQL query requests one or more fields.

type Author {
  # id, firstName, and lastName are all fields of the Author type
  id: Int!
  firstName: String
  lastName: String
}

querying

A request for specific data from a GraphQL server. Clients define the structure of the response, enabling precise and efficient data retrieval.

field

A unit of data that belongs to a type in a schema. Every GraphQL query requests one or more fields.

type Author {
  # id, firstName, and lastName are all fields of the Author type
  id: Int!
  firstName: String
  lastName: String
}

argument

A key-value pair associated with a particular schema field that lets operations pass data to that field's resolver.

Argument values can be hardcoded as literal values (shown below for clarity) or provided via GraphQL variables (recommended).

query GetHuman {
  human(id: "200") {
    name
    height(unit: "meters")
  }
}

field

A unit of data that belongs to a type in a schema. Every GraphQL query requests one or more fields.

type Author {
  # id, firstName, and lastName are all fields of the Author type
  id: Int!
  firstName: String
  lastName: String
}

query

A request for specific data from a GraphQL server. Clients define the structure of the response, enabling precise and efficient data retrieval.

resolvers

A function that populates data for a particular field in a GraphQL schema. For example:

const resolvers = {
  Query: {
    author(root, args, context, info) {
      return find(authors, { id: args.id });
    },
  },
};

field

A unit of data that belongs to a type in a schema. Every GraphQL query requests one or more fields.

type Author {
  # id, firstName, and lastName are all fields of the Author type
  id: Int!
  firstName: String
  lastName: String
}

arguments

A key-value pair associated with a particular schema field that lets operations pass data to that field's resolver.

Argument values can be hardcoded as literal values (shown below for clarity) or provided via GraphQL variables (recommended).

query GetHuman {
  human(id: "200") {
    name
    height(unit: "meters")
  }
}

query

A request for specific data from a GraphQL server. Clients define the structure of the response, enabling precise and efficient data retrieval.

argument

A key-value pair associated with a particular schema field that lets operations pass data to that field's resolver.

Argument values can be hardcoded as literal values (shown below for clarity) or provided via GraphQL variables (recommended).

query GetHuman {
  human(id: "200") {
    name
    height(unit: "meters")
  }
}

field

A unit of data that belongs to a type in a schema. Every GraphQL query requests one or more fields.

type Author {
  # id, firstName, and lastName are all fields of the Author type
  id: Int!
  firstName: String
  lastName: String
}

argument

A key-value pair associated with a particular schema field that lets operations pass data to that field's resolver.

Argument values can be hardcoded as literal values (shown below for clarity) or provided via GraphQL variables (recommended).

query GetHuman {
  human(id: "200") {
    name
    height(unit: "meters")
  }
}

argument

A key-value pair associated with a particular schema field that lets operations pass data to that field's resolver.

Argument values can be hardcoded as literal values (shown below for clarity) or provided via GraphQL variables (recommended).

query GetHuman {
  human(id: "200") {
    name
    height(unit: "meters")
  }
}

field

A unit of data that belongs to a type in a schema. Every GraphQL query requests one or more fields.

type Author {
  # id, firstName, and lastName are all fields of the Author type
  id: Int!
  firstName: String
  lastName: String
}

query

A request for specific data from a GraphQL server. Clients define the structure of the response, enabling precise and efficient data retrieval.

resolver

A function that populates data for a particular field in a GraphQL schema. For example:

const resolvers = {
  Query: {
    author(root, args, context, info) {
      return find(authors, { id: args.id });
    },
  },
};

NEW COURSE ALERT

Introducing Apollo Connectors

Connectors are the new and easy way to get started with GraphQL, using existing REST APIs.

Say goodbye to GraphQL servers and resolvers—now, everything happens in the schema!

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