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📝 As an app user, I want to see an individual user, so that I can focus on them.

We’ll need another root-level field named user. Since we’ve already got GraphQL completely set up, adding this field should be trivial. There will be one new concept. We’ll need to accept an ID parameter. In GraphQL, that is accomplished with the argument helper.

Add the user field to QueryType.

app/graphql/types/query_type.rb

module Types
  class QueryType < Types::BaseObject
    # Add `node(id: ID!) and `nodes(ids: [ID!]!)`
    include GraphQL::Types::Relay::HasNodeField
    include GraphQL::Types::Relay::HasNodesField

    # Add root-level fields here.
    # They will be entry points for queries on your schema.

    field :users, [Types::UserType], null: false,
      description: "List all users in email order"

    field :user, Types::UserType, "Find a user by ID", null: false do
      argument :id, ID
    end

    def users
      User.all.order(:email)
    end

    def user(id:)
      User.find(id)
    end
  end
end

Since find will raise an error if it fails to find a record, we need to handle that as well. Luckily, GraphQL documentation gives us some clear guidance on how to do that.

Add some global error handling.

app/graphql/all_hands_schema.rb (lines omitted)

class AllHandsSchema < GraphQL::Schema
  # ...

  rescue_from(ActiveRecord::RecordNotFound) do |err, obj, args, ctx, field|
    raise GraphQL::ExecutionError, "#{field.type.unwrap.graphql_name} not found"
  end

  # ...
end

Generate a test for our new field.

Terminal

bin/rails g integration_test types/query_type/user

Fill in the generated test.

test/integration/types/query_type/user_test.rb

require "test_helper"

class Types::QueryType::UserTest < ActionDispatch::IntegrationTest
  setup do
    @query = <<~GRAPHQL
      query User($id: ID!) {
        user(id: $id) {
          id
          name
          email
          createdAt
          updatedAt
        }
      }
    GRAPHQL
  end

  test "user" do
    user = users(:daniel)

    post graphql_path, params: { query: @query, variables: { id: user.id } }

    assert_equal(
      {
        "data" => {
          "user" => {
            "id" => user.id.to_s,
            "name" => user.name,
            "email" => user.email,
            "createdAt" => user.created_at.iso8601,
            "updatedAt" => user.updated_at.iso8601,
          },
        },
      },
      @response.parsed_body
    )
  end

  test "user not found" do
    post graphql_path, params: { query: @query, variables: { id: "0" } }

    assert_equal(
      {
        "data" => nil,
        "errors" => [
          {
            "message" => "User not found",
            "locations" => [{ "line" => 2, "column" => 3 }],
            "path" => ["user"],
          },
        ],
      },
      @response.parsed_body
    )
  end
end

This is only slightly more complicated than the previous test class. Here, we pass our arguments using the variables parameter. We also name our query and declare its variables. The same tests could be written using Ruby string interpolation, but this way is cleaner.

Run the new tests.

Terminal

bin/rails t test/integration/types/query_type/user_test.rb

Check for regressions by running all tests.

Terminal

bin/rails t

Success!

✅ Make a commit

✅ As an app user, I want to see an individual user, so that I can focus on them.

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Next: Chapter 5 - The Mutation