Scalars

Scalar types represent concrete values at the leaves of a query. For example in the following query the name field will resolve to a scalar type (in this case it’s a String type): 

{
  user {
    name
  }
}
  
{
  "data": {
    "user": {
      "name": "Patrick"
    }
  }
}

There are several built-in scalars, and you can define custom scalars too. (Enums are also leaf values.) The built in scalars are:

Fields can return built-in scalars by using the Python equivalent: 

import datetime
import decimal
import uuid
import strawberry




@strawberry.type
class Product:
    id: uuid.UUID
    name: str
    stock: int
    is_available: bool
    available_from: datetime.date
    same_day_shipping_before: datetime.time
    created_at: datetime.datetime
    price: decimal.Decimal
    void: None
  
type Product {
  id: UUID!
  name: String!
  stock: Int!
  isAvailable: Boolean!
  availableFrom: Date!
  sameDayShippingBefore: Time!
  createdAt: DateTime!
  price: Decimal!
  void: Void
}

Scalar types can also be used as inputs: 

import datetime
import strawberry




@strawberry.type
class Query:
    @strawberry.field
    def one_week_from(self, date_input: datetime.date) -> datetime.date:
        return date_input + datetime.timedelta(weeks=1)

Custom scalars

You can create custom scalars for your schema to represent specific types in your data model. This can be helpful to let clients know what kind of data they can expect for a particular field.

To define a custom scalar you need to give it a name and functions that tell Strawberry how to serialize and deserialise the type.

For example here is a custom scalar type to represent a Base64 string: 

import base64
from typing import NewType


import strawberry


Base64 = strawberry.scalar(
    NewType("Base64", bytes),
    serialize=lambda v: base64.b64encode(v).decode("utf-8"),
    parse_value=lambda v: base64.b64decode(v.encode("utf-8")),
)




@strawberry.type
class Query:
    @strawberry.field
    def base64(self) -> Base64:
        return Base64(b"hi")




schema = strawberry.Schema(Query)


result = schema.execute_sync("{ base64 }")


assert results.data == {"base64": "aGk="}
Note

The Base16 , Base32 and Base64 scalar types are available in strawberry.scalars 

from strawberry.scalars import Base16, Base32, Base64

Example JSONScalar

import json
from typing import Any, NewType


import strawberry


JSON = strawberry.scalar(
    NewType("JSON", object),
    description="The `JSON` scalar type represents JSON values as specified by ECMA-404",
    serialize=lambda v: v,
    parse_value=lambda v: v,
)

Usage: 

@strawberry.type
class Query:
    @strawberry.field
    def data(self, info) -> JSON:
        return {"hello": {"a": 1}, "someNumbers": [1, 2, 3]}
  
query ExampleDataQuery {
  data
}
  
{
  "data": {
    "hello": {
      "a": 1
    },
    "someNumbers": [1, 2, 3]
  }
}
Note

The JSON scalar type is available in strawberry.scalars 

from strawberry.scalars import JSON

Overriding built in scalars

To override the behaviour of the built in scalars you can pass a map of overrides to your schema.

Here is a full example of replacing the built in DateTime scalar with one that serializes all datetimes as unix timestamps: 

from datetime import datetime, timezone
import strawberry


# Define your custom scalar
EpochDateTime = strawberry.scalar(
    datetime,
    serialize=lambda value: int(value.timestamp()),
    parse_value=lambda value: datetime.fromtimestamp(int(value), timezone.utc),
)




@strawberry.type
class Query:
    @strawberry.field
    def current_time(self) -> datetime:
        return datetime.now()




schema = strawberry.Schema(
    Query,
    scalar_overrides={
        datetime: EpochDateTime,
    },
)
result = schema.execute_sync("{ currentTime }")
assert result.data == {"currentTime": 1628683200}

To override with a pendulum instance you’d want to serialize and parse_value like the above example. Let’s throw them in a class this time.

In addition we’ll be using the Union clause to combine possible input types. Since pendulum isn’t typed yet, we’ll have to silence mypy’s errors using # type: ignore 

import pendulum
from datetime import datetime




class DateTime:
    """
    This class is used to convert the pendulum.DateTime type to a string
    and back to a pendulum.DateTime type
    """


    @staticmethod
    def serialize(dt: Union[pendulum.DateTime, datetime]) -> str:  # type: ignore
        try:
            return dt.isoformat()
        except ValueError:
            return dt.to_iso8601_string()  # type: ignore


    @staticmethod
    def parse_value(value: str) -> Union[pendulum.DateTime, datetime]:  # type: ignore
        return pendulum.parse(value)  # type: ignore




date_time = strawberry.scalar(
    Union[pendulum.DateTime, datetime],  # type: ignore
    name="datetime",
    description="A date and time",
    serialize=DateTime.serialize,
    parse_value=DateTime.parse_value,
)

BigInt (64-bit integers)

Python by default allows, integer size to be 2^64. However the graphql spec has capped it to 2^32.

This will inevitably raise errors. Instead of using strings on the client as a workaround, you could use the following scalar: 

# This is needed because GraphQL does not support 64 bit integers
BigInt = strawberry.scalar(
    Union[int, str],  # type: ignore
    serialize=lambda v: int(v),
    parse_value=lambda v: str(v),
    description="BigInt field",
)

You can adapt your schema to automatically use this scalar for all integers by using the scalar_overrides parameter

Tip

Only use this override if you expect most of your integers to be 64-bit. Since most GraphQL schemas follow standardized design patterns and most clients require additional effort to handle all numbers as strings, it makes more sense to reserve BigInt for numbers that actually exceed the 32-bit limit. You can achieve this by annotating BigInt instead of int in your resolvers handling large python integers. 

user_schema = strawberry.Schema(
    query=Query,
    mutation=Mutation,
    subscription=Subscription,
    scalar_overrides={datetime: date_time, int: BigInt},
)