note-field.go

...

"note": &graphql.Field{
			Name:        "Get note by ID",
			Type:        noteType,
			Description: "Get note by ID",
			Args:        graphql.FieldConfigArgument{"id": &graphql.ArgumentConfig{Type: graphql.Int}},
			Resolve: func(params graphql.ResolveParams) (interface{}, error) {
				id, isValid := params.Args["id"].(int)
				if isValid {
					for _, note := range notes {
						if note.ID == id {
							return note, nil
						}
					}
				}
				return nil, nil
			},
		}, // Additional fields
}