Strange behaviour when using interface/implements (or unions)

Issues GraphQL
1

Sorry for the lenghty question, but it explains it best (you can try for yourself).
Given following docker-compose.yml:

version: '3.7'
services:
  zero:
    command: dgraph zero --my=zero:5080
    image: dgraph/dgraph:v20.11.1
    volumes:
    - bug-dgraph:/dgraph:rw
  dgraph:
    command: dgraph alpha --my=dgraph:7080 --zero=zero:5080 --graphql_lambda_url=http://remote:8686/graphql-worker --whitelist=0.0.0.0/0
    image: dgraph/dgraph:v20.11.1
    ports:
    - published: 8080
      target: 8080
    volumes:
    - bug-dgraph:/dgraph:rw
  remote:
    image: alpine
    command: ["/bin/sh","-c", 'while true; do echo -e "HTTP/1.1 200 OK\r\nConnection: close\r\nContent-Type: application/json\r\n\r\n{\"code\":100,\"message\":\"OK\",\"user\":{\"login\":\"john\",\"tenant\":{\"name\":\"NoName\"}}}" | nc -vl -p 8686 ; done']
  schema:
    image: curlimages/curl:7.75.0
    volumes:
    - garden-dgraph:/dgraph:rw
    command: ["-v", "-X", "POST", "http://dgraph:8080/admin/schema","--data-binary","@schema.graphql"]
    volumes:
    - ./schema.graphql:/schema.graphql:ro
volumes:
  bug-dgraph: {}

and following schema.graphql:

interface Event {
  id: ID!
  created_at: DateTime!
  name: String! @search(by: [hash])
  comment: String
  created_by: User!
}

type TenantCreatedEvent implements Event {
  tenant: Tenant!
  tenant_name: String!
}

type TenantModifiedEvent implements Event {
  Atenant: Tenant!
  tenant_name: String!
}

type Tenant {
  id: ID!
  name: String! @search(by: [hash])
}

type User @secret(field:"password") {
  login: String! @id @search(by: [hash])
  first_name: String! @search(by: [hash])
  last_name: String! @search(by: [hash]) 
  tenant: Tenant
}

type UserPayload @remote {
  status: Boolean!
  code: Int!
  message: String
  error: String
  user: User
}

type EmailVerificationPayload @remote {
  status: Boolean!
  code: Int!
  message: String
  error: String
  user: User
}

type ResponsePayload @remote {
  status: Boolean!
  code: Int!
  error: String
  message: String
}

type Query {
  verifyEmail(email:String!,code:String!): EmailVerificationPayload @lambda
}

# Dgraph.Authorization {"VerificationKey":"my_secret","Header":"X-Auth-Token","Namespace":"localhost","Algo":"HS256"}

when running it:
docker-compose up -d; sleep 10; docker-compose up
(where sleep is to wait for graphql endpoint readiness, then another docker-compose up for POSTing the new schema)
and then querying with insomnia for:

{
  verifyEmail(email:"test",code:"test") {
    code
    error
    message
    user {
      login
      tenant {
        name
      }
    }  
  }
}

I get following result:

{
  "data": {
    "verifyEmail": {
      "code": 100,
      "error": null,
      "message": "OK",
      "user": {
        "login": "john",
        "tenant": {
          "name": "NoName"
        }
    }
  }
}

Then when changing Atenant to tenant in TenantModifiedEvent and reloading the schema (with docker-compose up -d) and repeating the query I get:

{
  "data": {
    "verifyEmail": {
      "code": 100,
      "error": null,
      "message": "OK",
      "user": {
        "login": "john",
        "tenant": null
      }
    }
  }
}

So I have 2 questions:

  • Can I use the predicates with the same name (tenant) in different types implementing common interface? (I guess not)
  • Why in the above examples the User.tenant is affected (returns null) when two other unrelated types implement predicates with the same name? I consider this as a bug.

Update: I experience similar unwanted side effect when using union instead of interface