GraphQL Schema 3

An implementation of GraphQL's type system in Dart, with no dependency beyond collection and source_span. Supports any platform where Dart runs. The decisions made in the design of this library were done to make the experience as similar to the JavaScript reference implementation as possible, and to also correctly implement the official specification.

Contains functionality to build all GraphQL types:

• String
• Int
• Float
• Boolean
• GraphQLObjectType
• GraphQLUnionType
• GraphQLEnumType
• GraphQLInputObjectType
• Date - ISO-8601 Date string, deserializes to a Dart DateTime object

Of course, for a full description of GraphQL's type system, see the official GraphQL Specification. Mostly analogous to graphql-js; many names are verbatim.

Where this comes from

This package is a fork of the GraphQL stack maintained as part of Angel3, which itself descends from the graphql_* packages Tobe O wrote for Angel. The fork is taken from the 2 line; the original BSD-3-Clause licence and its copyright notice are kept verbatim in LICENSE, and the bulk of the type system, the parser and the execution algorithm are still that work.

Why fork at all. Two reasons, and only the second one still holds:

• Upstream had stopped moving while the projects depending on it had not. Development there has since resumed, but by then the two lines had diverged far enough that merging back would cost more than it returns.
• The stack was pinned to angel3_*, and angel3_* decided which analyzer and which Dart SDK everything downstream could use. That is what held the generator seven analyzer majors back for months. Cutting the tie was the point of the 3 line.

So: the 3 line does not track upstream and does not merge from it. It is maintained on its own, with three rules - as few dependencies as possible, no dependency that dictates the SDK, and no behaviour without a test covering it.

The 3 is a lineage marker, not a version and not a succession

graphql_schema2 is not this package's predecessor. It is its sibling, and it is alive: 7.0.0 as of August 2026, published by dukefirehawk.com, on its own numbering that long ago stopped matching the 2 in its name. The 3 here says only which line this fork was taken from.

If you want the upstream package, take graphql_schema2. Take this one for the smaller dependency tree and the fixes listed below. They have not been offered upstream. The two lines were compared at upstream 7.0.0: every release it has cut since the fork point raises the Dart SDK floor or the linter, and its dependency set is unchanged.

What version 3 changed

Two dependencies, collection and source_span.

Six bugs, all of them reachable from a client request:

• Validating an unknown enum literal raised Bad state: No element instead of returning a failed ValidationResult. For a string-valued enum, built with enumTypeFromStrings, every literal took that path, so any client sending an unrecognised value crashed the resolver.
• A field whose input had the wrong type raised a cast error while validating an object rather than reporting the mismatch.
• Float rejected an integer literal. The specification coerces an integer to Float, and only in that direction.
• GraphQLFieldInput.operator == compared other.defaultValue with itself, so two inputs differing only by their default compared as equal.
• Four types hashed the identity of their field list while comparing its contents, so two equal instances could carry different hash codes. That breaks the Object contract and, with it, any Set or Map keyed on a type.
• GraphQLObjectType.hashCode and GraphQLInputObjectType.hashCode folded name in twice and never description.

Also: quiver removed, its hash2 / hash3 / hash4 replaced by Object.hash; and a test suite of 41 tests, where there were none.

The full list is in CHANGELOG.md.

Installation

dart pub add graphql_schema3

Usage

It's easy to define a schema with the helper functions:

final GraphQLSchema todoSchema = GraphQLSchema(
    query: objectType('Todo', [
  field('text', graphQLString.nonNullable()),
  field('created_at', graphQLDate)
]));

All GraphQL types are generic, in order to leverage Dart's strong typing support.

Serialization

GraphQL types can serialize and deserialize input data. The exact implementation of this depends on the type.

var iso8601String = graphQLDate.serialize(DateTime.now());
var date = graphQLDate.deserialize(iso8601String);
print(date.millisecondsSinceEpoch);

Validation

GraphQL types can validate input data.

var validation = myType.validate('@root', {...});

if (validation.successful) {
  doSomething(validation.value);
} else {
  print(validation.errors);
}

Helpers

• graphQLSchema - Create a GraphQLSchema
• objectType - Create a GraphQLObjectType with fields
• field - Create a GraphQLField with a type/argument/resolver
• listOf - Create a GraphQLListType with the provided innerType
• inputObjectType - Creates a GraphQLInputObjectType
• inputField - Creates a field for a GraphQLInputObjectType

Types

All of the GraphQL scalar types are built in, as well as a Date type:

• graphQLString
• graphQLId
• graphQLBoolean
• graphQLInt
• graphQLFloat
• graphQLDate

Non-Nullable Types

You can easily make a type non-nullable by calling its nonNullable method.

List Types

Support for list types is also included. Use the listType helper for convenience.

/// A non-nullable list of non-nullable integers
listOf(graphQLInt.nonNullable()).nonNullable();

Input values and parameters

Take the following GraphQL query:

{
   anime {
     characters(title: "Hunter x Hunter") {
        name
        age
     }
   }
}

And subsequently, its schema:

type AnimeQuery {
  characters($title: String!): [Character!]
}

type Character {
  name: String
  age: Int
}

The field characters accepts a parameter, title. To reproduce this in package:graphql_schema3, use GraphQLFieldInput:

final GraphQLObjectType queryType = objectType('AnimeQuery', fields: [
  field('characters',
    listOf(characterType.nonNullable()),
    inputs: [
      new GraphQLFieldInput('title', graphQLString.nonNullable())
    ]
  ),
]);

final GraphQLObjectType characterType = objectType('Character', fields: [
  field('name', graphQLString),
  field('age', graphQLInt),
]);

In the majority of cases where you use GraphQL, you will be delegate the actual fetching of data to a database object, or some asynchronous resolver function.

package:graphql_schema3 includes this functionality in the resolve property, which is passed a context object and a Map<String, dynamic> of arguments.

A hypothetical example of the above might be:

var field = field(
  'characters',
  graphQLString,
  resolve: (_, args) async {
    return await myDatabase.findCharacters(args['title']);
  },
);