What is it

Data passed to schema's resolver/field.

• Argument values can be hardcoded as a value or passed via GraphQL input variable.

# schema definition
type Query {
  resources: [Resource!]!
  resource(format: DataFormat!): Resource!
}

# client query
query GetResource {
  resource(format: "jpeg") {
    id
    data
  }
}

• resources field returns array of Resource type data
  • Corresponding resolver does not take an input
• resource field returns object of Resource type after taking in format argument
  • Resolvers consumes the input value and executes function

input

argument/input allows user to narrow down the data returned.

• Query fields are an all-or-nothing return.
• We can only get back predefined results.

# schema definition field
resource(format: DataFormat!): Resource!

• resource is the field name
• format is the argument name
• DataFormat would be the argument's data type
  • ! makes it non-nullable required argument
  • will result in error when other types are passed
• Resource would be the return data type on the field
  • ! makes it non-nullable required return type

input type can be a scalar or an object.

# server/schema.graphql example of object input
input SearchListingsInput {
  checkInDate: String!
  checkOutDate: String!
  numOfBeds: Int
  page: Int
  limit: Int
  sortBy: SortByCriteria # enum type
}

type Query {
  searchListings(criteria: SearchListingsInput): [Listing]! 
}

Client using input

The argument on the client query and the schema can be named anything.

• It does not have to match the field name on the schema

# query
query getUserPosts($userId: ID!, $postLimit: Int!) {
  user(id: $userId) {
    name
    posts(limit: $postLimit) {
      title
      content
    }
  }
}

# schema
# Root query is identical
schema {
  query: Query
}

# Define the root query type
type Query {
  user(id: ID!): User
}

# Define the custom types
type User {
  id: ID!
  name: String!
  posts(limit: Int!): [Post!]!
}

type Post {
  id: ID!
  title: String!
  content: String!
}