GraphQL Query Template Language

This Go package provides a parser for GQT, the GraphQL Query Template language which is used by Graph Guard for defining GraphQL query templates in a flexible and human-friendly way.

A GQT template declaratively defines the constraints of both the structure and input values of a GraphQL operation.

# This is a GQT query template example.
query {
  # Allow selecting a user with any id.
  user(id: *) {
    id
    name
    max 2 { # Allow a maximum of 2 selections out of this set.
      birthdate
      email
      address {country city street}
    }
    # Allow a maximum limit of 100 friends.
    friends(after: *, limit=$friendsLimit: < 100) {
      id name birthdate email
      # Allow a maximum limit of 100 friends in total with a maximum depth of 2.
      # limit is restricted to a maximum value of 100 divided by the limit above.
      friends(after: *, limit: < 100 / $friendsLimit) {
        id name birthdate email
      }
    }
    pictures(
      # Allow a string with a maximum byte length of 64.
      prefix: len <= 64,
      # Allow an array with a maximum of 8 items,
      # where each item string is not longer than 64 bytes.
      tags: len < 8 && [...len < 64],
      # Allow only a subset of possible enum values in the category argument.
      category: PUBLIC || FRIENDSONLY,
      # Allow a rating value between 10 and 20
      rating: > 10 && < 20, 
    ) { url }
  }
}

GraphQL Schema:

# This is a GQT query template example.
scalar Date
enum PictureCategory {
    PUBLIC
    FRIENDSONLY
    PRIVATE
}
type Query { user(id: ID!): User }
type User {
    id:        ID!
    name:      String
    birthdate: Date
    email:     String
    address:   Address
    friends(
        after: ID,
        limit: Int!,
    ): [User!]!
    pictures(
        prefix:   String,
        tags:     [String!],
        category: PictureCategory,
        rating:   Int,
    ): [Picture!]
}
type Address {
    country: String!
    city:    String!
    street:  String!
}
type Picture { url: String! }

Features

• Flexible restriction of the structure of a GraphQL request including max depth.
• Intuitive GraphQL-like syntax.
• Schema-aware mode with full type checking and validation.
• Schemaless mode (no validation against a GraphQL schema).
• Arithmetic and boolean expressions in input value constraints.
• Restriction of the maximum number of selections inside a max set.

Full documentation is available at docs.graphguard.io/gqt.