联合类型无法在运行时解析对象类型

Question

我正在使用 Starlette 和 Graphene 使用 Python 设置 GraphQL 服务器，但遇到了一个我找不到解决方案的问题。 Graphene Documentation 没有详细介绍我正在尝试实现的联合类型。 我根据石墨烯文档设置了一个最小示例，您可以运行它来复制此问题

import os

import uvicorn
from graphene import ObjectType, Field, List, String, Int, Union
from graphene import Schema
from starlette.applications import Starlette
from starlette.graphql import GraphQLApp
from starlette.routing import Route

mock_data = {
    "episode": 3,
    "characters": [
        {
            "type": "Droid",
            "name": "R2-D2",
            "primaryFunction": "Astromech"
        },
        {
            "type": "Human",
            "name": "Luke Skywalker",
            "homePlanet": "Tatooine"
        },
        {
            "type": "Starship",
            "name": "Millennium Falcon",
            "length": 35
        }
    ]
}


class Human(ObjectType):
    name = String()
    homePlanet = String()


class Droid(ObjectType):
    name = String()
    primary_function = String()


class Starship(ObjectType):
    name = String()
    length = Int()


class Characters(Union):
    class Meta:
        types = (Human, Droid, Starship)


class SearchResult(ObjectType):
    characters = List(Characters)
    episode = Int()


class RootQuery(ObjectType):
    result = Field(SearchResult)

    @staticmethod
    def resolve_result(_, info):
        return mock_data


graphql_app = GraphQLApp(schema=Schema(query=RootQuery))

routes = [
    Route("/graphql", graphql_app),
]

api = Starlette(routes=routes)

if __name__ == "__main__":
    uvicorn.run(api, host="127.0.0.1", port=int(os.environ.get("PORT", 8080)))

如果您随后转到 http://localhost:8080/graphq 并输入以下查询

query Humans{
  result {
    episode
    characters {
      ... on Human {
        name
      }
    }
  }
}

我收到此错误

 {
    "data": {
        "result": {
            "episode": 3,
            "characters": null
        }
    },
    "errors": [
        {
            "message": "Abstract type Characters must resolve to an Object type at runtime for field SearchResult.characters with value \"[{'type': 'Droid', 'name': 'R2-D2', 'primaryFunction': 'Astromech'}, {'type': 'Human', 'name': 'Luke Skywalker', 'homePlanet': 'Tatooine'}, {'type': 'Starship', 'name': 'Millennium Falcon', 'length': 35}]\", received \"None\".",
            "locations": [
                {
                    "line": 4,
                    "column": 5
                }
            ]
        }
    ]
}

我现在被困住了。也许有人已经这样做了并且可以提供帮助？ 如何在运行时解决此问题。我已经尝试过不同的方法，例如我更改了 Character 和 RootQuery 类：

class Character(Union):
    class Meta:
        types = (Human, Droid, Starship)

    def __init__(self, data, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.data = data
        self.type = data.get("type")

    def resolve_type(self, info):
        if self.type == "Human":
            return Human
        if self.type == "Droid":
            return Droid
        if self.type == "Starship":
            return Starship


class RootQuery(ObjectType):
    result = Field(SearchResult)
    
    @staticmethod
    def resolve_result(_, info):
        return {**mock_data, "characters": [Character(character) for character in mock_data.get('characters')]}

导致

{
    "data": {
        "result": {
            "episode": 3,
            "characters": [
                {},
                {
                    "name": null
                },
                {}
            ]
        }
    }
}

任何想法都将不胜感激！

Answer 1

jkimbo 回答了问题here:

class Character(Union):
    class Meta:
        types = (Human, Droid, Starship)

    @classmethod
    def resolve_type(cls, instance, info):
        if instance["type"] == "Human":
            return Human
        if instance["type"] == "Droid":
            return Droid
        if instance["type"] == "Starship":
            return Starship


class RootQuery(ObjectType):
    result = Field(SearchResult)

    def resolve_result(_, info):
        return mock_data

注意我只是返回 mock_data 并且我已经更新了 resolve_type 方法以根据数据进行切换。 Union 类型使用与 Interface 相同的 resolve_type 方法来确定在运行时要解析为哪种类型：https://docs.graphene-python.org/en/latest/types/interfaces/#resolving-data-objects-to-types