标量

标量类型表示查询叶部分的具体值。例如，在下面的查询中，name 字段将解析为标量类型（在这种情况下，它是 String 类型）：

Loading GraphiQL...

{ user { name } }

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

有几个内置的标量，也可以定义自定义标量。（Enums也是叶值。）内置的标量是：

• String, maps to Python’s str

• Int, a signed 32-bit integer, maps to Python’s int

• Float, a signed double-precision floating-point value, maps to Python’s float

• Boolean, true or false, maps to Python’s bool

• ID, a specialised String for representing unique object identifiers

• Date, an ISO-8601 encoded date

• DateTime, an ISO-8601 encoded datetime

• Time, an ISO-8601 encoded time

• Decimal, a Decimal value serialized as a string

• UUID, a UUID value serialized as a string

• Void, always null, maps to Python’s None

字段可以通过使用 Python 等效函数返回内置标量：

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
}

标量类型也可以用作输入：

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)

自定义标量

可以为模式创建自定义标量，以表示数据模型中的特定类型。这有助于让客户知道对于特定的字段可以期望得到什么样的数据。要自定义标量，您需要给它名称和函数，告诉 Strawberry 如何序列化和反序列化该类型。例如，这里有自定义标量类型来表示 Base64 字符串：

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="}

备注

Base16、Base32 和 Base64 标量类型在 strawberry.scalars 中可用

from strawberry.scalars import Base16, Base32, Base64

JSONScalar 示例

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,
)

用法：

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

Loading GraphiQL...

{ ExampleDataQuery { data } }

{ "data": { "hello": { "a": 1 }, "someNumbers": [1, 2, 3] } }

备注

JSON 标量类型在 strawberry.scalars 中可用。

from strawberry.scalars import JSON

覆盖内置的标量

要覆盖内置标量的行为，可以将覆盖映射传递给您的模式。下面是完整的例子，将内置的 DateTime 标量替换为将所有 datetimes 序列化为 unix 时间戳的标量：

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}