中继订阅错误：预期为null的是GraphQL复合类型

Question

I want to create a subscription, but when I am compiling to relay I am getting this error: ERROR: Expected null to be a GraphQL composite type.

I think what my graphql definition is wrong, but I have no clue about how to check it. Sadly the documentation at relay site is too simple. Do you know what are the rules in order to create a proper graphql for a subscription?

Answer 1

In theory the file schema.graphql is autogenerated, but I can't find how to add a subscription in it from tools.

I followed this tutorial and manually added a type for the subscriptions adapting this schema file to my case. This is my final schema file:

type Subscription {
  Story(filter: StorySubscriptionFilter): StorySubscriptionPayload
}

input StorySubscriptionFilter {
  mutation_in: [_ModelMutationType!]
}

type StorySubscriptionPayload {
  mutation: _ModelMutationType!
  node: Story
  updatedFields: [String!]
  previousValues: StoryPreviousValues
}

enum _ModelMutationType {
  CREATED
  UPDATED
  DELETED
}

type StoryPreviousValues {
  createdAt: DateTime!
  id: ID!
  updatedAt: DateTime!
}

Answer 2

Expected null to be a GraphQL composite type.

Above error simply means that you are missing a type in the schema you are using for compiling that you are using in your code.

One of the easiest way to get the latest updated schema matching with the GraphQL server is to use get-graphql-schema

get-graphql-schema graphql server url > schema.graphql

replace graphql server url with the actual url

and then use the updated schema.graphql for compiling

yarn relay-compiler --src ./src --schema schema.graphql