graphene-python学习笔记（6）Interface

一、Interface

基础：

（1）任意定义实施了接口的ObjectType都将具有接口的字段。

（2）接口可以让你返回一个或一组不同的类的实例。根据运行时的参数决定返回哪一个实施了接口的ObjectType

示例：

定义接口：

import graphene

class Character(graphene.Interface):
    id = graphene.ID(required=True)
    name = graphene.String(required=True)
    friends = graphene.List(lambda: Character)

　　2、实施接口

class Human(graphene.ObjectType):
    class Meta:
        interfaces = (Character, )

    starships = graphene.List(Starship)
    home_planet = graphene.String()

class Droid(graphene.ObjectType):
    class Meta:
        interfaces = (Character, )

    primary_function = graphene.String()

　　相当于：

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

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

type Droid implements Character {
    id: ID!
    name: String!
    friends: [Character]
    primaryFunction: String
}

　　3、根据接口返回不同的类

class Query(graphene.ObjectType):
    hero = graphene.Field(
        Character,
        required=True,
        episode=graphene.Int(required=True)
    )

    def resolve_hero(_, info, episode):
        # Luke is the hero of Episode V
        if episode == 5:
            return get_human(name='Luke Skywalker')
        return get_droid(name='R2-D2')

schema = graphene.Schema(query=Query, types=[Human, Droid])

　　这样Query将根据查询时hero的参数决定是返回Human还是Droid。

使用inlinne fragement进行查询

query HeroForEpisode($episode: Int!) {
    hero(episode: $episode) {
        __typename
        name
        ... on Droid {
            primaryFunction
        }
        ... on Human {
            homePlanet
        }
    }
}

　　当参数是{ "episode": 4 }返回

{
    "data": {
        "hero": {
            "__typename": "Droid",
            "name": "R2-D2",
            "primaryFunction": "Astromech"
        }
    }
}

　　当参数是{ "episode": 5 }时返回

{
    "data": {
        "hero": {
            "__typename": "Human",
            "name": "Luke Skywalker",
            "homePlanet": "Tatooine"
        }
    }
}

　　当您在Graphene中构建schema时，解析器通常会返回表示支持GraphQL类型的数据的对象，而不是Graphene类型的实例（例如Django或SQLAlchemy模型）。这适用于ObjectType和Scalar字段，但是当您开始使用接口时，您可能会遇到此错误：

"Abstract type Character must resolve to an Object type at runtime for field Query.hero ..."

　　未解决上面的问题，我们需要定义一个resolve_type

class Character(graphene.Interface):
    id = graphene.ID(required=True)
    name = graphene.String(required=True)

    @classmethod
    def resolve_type(cls, instance, info):
        if instance.type == 'DROID':
            return Droid
        return Human

　　将data object转变为graphene type