Epoxy

Epoxy is a magical tool for rapid development of GraphQL types, schemas, resolvers, mutations quickly & pragmatically.

• Minimal Boilerplate: You can create a GraphQL schema and execute it in less than 5 lines of code.
• Definition Ordering: It doesn't matter. Define your objects in any order you want. Epoxy will take care of the rest.
• Quick: Once you create your schema, epoxy doesn't get in the way. Your resolvers will be called directly by graphql-core with no additional indirection.

Installation

Epoxy is available on pypi under the package name graphql-epoxy, you can get it by running:

pip install graphql-epoxy

Usage

Defining a GraphQL Schema using Epoxy is as simple as creating a TypeRegistry and using it to create types for you.

from epoxy import TypeRegistry
R = TypeRegistry()

class Character(R.Interface):
    id = R.ID
    name = R.String
    friends = R.Character.List
    

class Human(R.Implements.Character):
    home_planet = R.String.NonNull
    
    
class Query(R.ObjectType):
    human = R.Human
    foo = R.Foo  # This is defined below! Ordering doesn't matter! 
    
    def resolve_human(self, obj, args, info):
        """This will be used as the description of the field Query.human."""
        return Human(id=5, name='Bob', friends=[Human(id=6, name='Bill')]

You can even have epoxy learn about your already defined Python enums.

class MoodStatus(enums.Enum):
    HAPPY = 1
    SAD = 2
    MELANCHOLY = 3


R(MoodStatus)

And then use it in an ObjectType:

class Foo(R.ObjectType):
    mood = R.MoodStatus
    # or 
    mood = R.Field(R.MoodStatus, description="Describing the mood of Foo, is sometimes pretty hard.")

    def resolve_mood(self, *args):
        return MoodStatus.HAPPY.value

Schema is a GraphQLSchema object. You can now use it with graphql:

schema = R.schema(R.Query)

result = graphql(schema, '''
{
    human {
        id
        name
        homePlanet
        friends {
            name
            homePlanet
        }
        
    }
}
''')

The schema is now defined as:

enum MoodStatus {
    HAPPY
    SAD
    MELANCHOLY
}

interface Character {
    id: ID
    name: String
    friends: [Character]
}

type Human implements Character {
    id: ID
    name: String
    friends: [Character]
    homePlanet: String!
}

type Foo {
    mood: MoodStatus
}

type Query {
    human: Human
    foo: Foo
}

Notice that epoxy converted snake_cased fields to camelCase in the GraphQL Schema.

ObjectTypes become containers

You can bring your own objects, (like a Django or SQLAlchemy model), or you can use the class you just created:

me = Human(id=2, name='Jake', home_planet='Earth', friends=[Human(id=3, name='Syrus', home_planet='Earth')])

print(me) # <Human id=2, name='Jake', home_planet='Earth', friends=[<Human id=3, name='Syrus', home_planet='Earth', friends=[]>]]>
print(me.name) # Jake

Epoxy will automatically resolve the runtime types of your objects if class that you created from R.ObjectType, but if you want to bring your own Human (i.e. a model.Model from Django), just tell Epoxy about it! And if you don't want to, you can just override the is_type_of function inside Human to something more to your liking.

my_app/models.py

from django.db import models
from my_app.graphql import R

@R.Human.CanBe
class RealHumanBean(models.Model):
    """
    And a real hero.
    """
    name = models.CharField(name=Name)


# Or if you don't want to use the decorator:
R.Human.CanBe(Human)

Mutations

Epoxy also supports defining mutations. Making a Mutation a Relay mutation is as simple as changing R.Mutation to Relay.Mutation.

class AddFriend(R.Mutation):
    class Input:
        human_to_add = R.ID.NonNull

    class Output:
        new_friends_list = R.Human.List

    @R.resolve_with_args
    def resolve(self, obj, human_to_add):
        obj.add_friend(human_to_add)
        return self.Output(new_friends_list=obj.friends)


schema = R.schema(R.Query, R.Mutations)

You can then execute the query:

mutation AddFriend {
    addFriend(input: {humanToAdd: 6}) {
        newFriendsList {
            id
            name
            homePlanet
        }
    }
}

Defining custom scalar types:

class DateTime(R.Scalar):
    @staticmethod
    def serialize(dt):
        return dt.isoformat()

    @staticmethod
    def parse_literal(node):
        if isinstance(node, ast.StringValue):
            return datetime.datetime.strptime(node.value, "%Y-%m-%dT%H:%M:%S.%f")

    @staticmethod
    def parse_value(value):
        return datetime.datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%f")

Defining input types:

class SimpleInput(R.InputType):
    a = R.Int
    b = R.Int
    some_underscore = R.String
    some_from_field = R.String(default_value='Hello World')

Defining an Enum (using enum module)

from enum import Enum

@R
class MyEnum(Enum):
    FOO = 1
    BAR = 2
    BAZ = 3

Starwars?!

Use the force, check out how we've defined the schema for the starwars tests, and compare them to the reference implementation's schema.

Relay Support

At this point, Epoxy has rudimentary relay support. Enable support for Relay by mixing in the RelayMixin using TypeResolver.Mixin.

from epoxy.contrib.relay import RelayMixin
from epoxy.contrib.relay.data_source.memory import InMemoryDataSource

# Epoxy provides an "in memory" data source, that implements `epoxy.contrib.relay.data_source.BaseDataSource`,
# which can be used to easily create a mock data source. In practice, you'd implement your own data source.
data_source = InMemoryDataSource()

R = TypeRegistry()
Relay = R.Mixin(RelayMixin, data_source)

Node Definition

Once RelayMixin has been mixed into the Registry, things can subclass Node automatically!

class Pet(R.Implements[Relay.Node]):
    name = R.String
    

Connection Definition & NodeField

Connections can be defined upon any object type. Here we'll make a Query root node that provides a connection to a list of pets & a node field to resolve an indivudal node.

class Query(R.ObjectType):
    pets = Relay.Connection('Pet', R.Pet) # The duplicate 'Pet' definition is just temporary and will be removed.
    node = Relay.NodeField

Mutations

class SimpleAddition(Relay.Mutation):
    class Input:
        a = R.Int
        b = R.Int

    class Output:
        sum = R.Int

    def execute(self, obj, input, info):
        return self.Output(sum=input.a + input.b)

Adding some data!

Let's add some pets to the data_source and query them!

# Schema has to be defined so that all thunks are resolved before we can use `Pet` as a container.
Schema = R.Schema(R.Query)

pet_names = ["Max", "Buddy", "Charlie", "Jack", "Cooper", "Rocky"]

for i, pet_name in enumerate(pet_names, 1):
    data_source.add(Pet(id=i, name=pet_name))

Running Relay Connection Query:

result = graphql(Schema, '''
{
    pets(first: 5) {
        edges {
            node {
                id
                name
            }
            cursor
        }
        pageInfo {
            hasPreviousPage
            hasNextPage
            startCursor
            endCursor
        }
    }
    node(id: "UGV0OjU=") {
        id
        ... on Pet {
            name
        }
    }
}
''')