Table of Contents


This gem includes its own implementation of a GraphQL parser, written using Ruby C API, which delivers the best performance possible.

It’s unlikely that you will need to use the parser on its own. However, by calling the parser independently, you can always check what the gem will understand from your GraphQL documents.

:001 > GQLParser.parse_execution('{ welcome }')
    => [[[nil, nil, nil, nil,
         [["welcome", nil, nil, nil, nil]]
       ]], nil]

You can also use it to check the current supporting spec version:

:001 > GQLParser::VERSION
    => "October 2021"

You can check the full implementation here.


The idea of the parser is to turn all the document information into arrays of predefined sizes where the needed information will always be in a given spot.

On top of that, Arrays and many other objects that may appear as a result will be wrapped by a SimpleDelegator named GQLParser::Token, so that their value and usage are kept regularly and enhanced with information about their meaning and place in the document.


There are several things a token can inform us of besides its underline value.

:001 > result = GQLParser.parse_execution('query Sample { welcome }')
    => [[["query", "Sample", nil, nil, [["welcome", nil, nil, nil, nil]]]], nil]
:002 > operation = result.dig(0, 0)
    => ["query", "Sample", nil, nil, [["welcome", nil, nil, nil, nil]]]
:003 > operation.class
    => GQLParser::Token
:004 > operation.type
    => :query
:005 > operation.begin_line
    => 1
:006 > operation.end_column
    => 25
:007 > operation.of_type?(:query)
    => true

The available methods are: type, begin_line, begin_column, end_line, end_column, and of_type?.

Quick reference

Here is a quick reference list of the token types and arrays returned by the parser:


[[*operation], [*fragment]]
[type, name, [*variable], [*directive], [*field]]
[name, type, [*directive], [*field]]
[name, type, value, [*directive]]
[name, [*argument]]
[name, alias, [*argument], [*directive], [*field]]
[name, array_dimensions, bitwise_nullability]
[name, value, variable_name]
[name, type, [*directive], [*field]]


To be implemented

The Type token

There are a couple of things important to notice when reading the information from the Type token. Types can have multiple dimensions of an Array, and each can have its own identifier of nullability. Those two information were simplified into 2 values:

array_dimensions: A simple integer that shows how many dimensions the array have.

For example:

String     # 0 dimensions
[String]   # 1 dimension
[[String]] # 2 dimensions

bitwise_nullability: An integer that represents the bitwise result of the nullability of each dimension

For example:

String      #  0 as 0
String!     #  1 as 1
[String]    # 00 as 0
[String]!   # 01 as 1
[String!]   # 10 as 2
[String!]!  # 11 as 3