subscriptions.md

title
Subscriptions

A Subscription type cannot be stitched from downstream services so it must be defined directly in the gateway schema.

Learn more about defining a Subscription type

Warning: Subscription stitching is coming in v13

After adding a Subscription type to the gateway service, you may encounter an error when building the gateway schema.

1. The schema builder was unable to identify the query type of the schema. Either specify which type is the query type or set the schema builder to non-strict validation mode.

If you turn off strict validation and generate the schema, the schema element won't include a query field despite a Query type being defined.

services
    .AddGraphQLServer()
    .ModifyOptions(o =>
        {
            o.StrictValidation = false;
        }
    )

schema {
  subscription: Subscription
}

type Query {
  messages: [Message!]!
}

To resolve this issue, use the Schema Options to specify the QueryTypeName and MutationTypeName.

services
    .AddGraphQLServer()
    .ModifyOptions(o =>
        {
            o.QueryTypeName = "Query";
            o.MutationTypeName = "Mutation";
        }
    )

Generating the schema again results in a valid schema.

schema {
  query: Query
  subscription: Subscription
}

type Query {
  messages: [Message!]!
}

type Subscription {
  onMessagePosted: Message!
}