gatsby-schema.gql

union FileOrMarkdown = LocalFile | MarkdownRemark

# types don't need to be fully defined
# field types that are not defined will be inferred
type MarkdownRemark {
  #force frontmatter field type so we can define field types
  frontmatter: frontmatter 
}

type frontmatter {
  # direct values
  string: String
  int: Int
  date: Date
  arrayOfString: [String] 
  arrayOfNumbers: [Int]
  notUsedField: String
  customType: CustomType

  # linked nodes
  localFile: LocalFile 
  union: FileOrMarkdown
}

type CustomType {
  string: String
  float: Float
  int: Int
  bool: Boolean
}