Can I add data to a GraphQL edge? - graphql

Question

I'm playing around with GraphQL, and I've run across the concept of connections and edges.
From what I understand it's not uncommon to see metadata on the connection, like the totalCount property in the following snippet.
type UserFriendsConnection {
pageInfo: PageInfo!
edges: [UserFriendsEdge]
totalCount: Int
}
My questions is whether it's OK to put arbitrary metadata on the edge also, and if the following would be a decent way to do that.
I felt like a query and a response would best illustrate what I'm looking for. It's the role property I want to place somewhere that makes sense.
I feel like it doesn't belong in the User type since the role describes the type of connection/relationship the User has with a Group.
# Query
{
me {
id
name
groupsConnection {
edges {
node {
id
name
membersConnection {
edges {
node {
id
name
}
role <--- HERE
}
}
}
role <--- HERE
}
}
}
}
# Response
{
"data": {
"me": {
"id": "1Edj3hZFg",
"name": "John Doe",
"groupsConnection": {
"edges": [
{
"node": {
"id": "bpQgdZweQE",
"name": "Fishing Team",
"membersConnection": {
"edges": [
{
"node": {
"id": "1Edj3hZFg",
"name": "John Doe"
},
"role": "ADMINISTRATOR" <--- HERE
},
{
"node": {
"id": "7dj37dH2d",
"name": "Rebecca Anderson"
},
"role": "MEMBER" <--- HERE
}
]
}
},
"role": "ADMINISTRATOR" <--- HERE
}
]
}
}
}
}

Answer 1

Connections are part of the Relay specification. Relay itself is a GraphQL client, although you can have a Relay-compliant GraphQL server without actually using Relay on the front end. According to the spec:
Edge types must have fields named node and cursor. They may have additional fields related to the edge, as the schema designer sees fit.
It's common enough to see additional fields on these types and it certainly makes sense. One word of caution though. If we have a User type, we may create a UserConnection and a UserEdge:
type UserConnection {
pageInfo: PageInfo!
egdes: [UserEdge!]!
}
type UserEdge {
cursor: String!
edge: User!
}
We can then use that connection type in all sorts of places...
type Query {
allUsers: UserConnection!
# other fields
}
type Group {
members: UserConnection!
# other fields
}
type User {
coworkers: UserConnection!
# other fields
}
However, if you add a field like role to UserEdge, that field will only make sense in the context of the members field on the Group type. It would have to return null or some dummy value in all other contexts, which can introduce unnecessary confusion.
That means, if you're going to introduce extra fields on your edge type that are relationship-dependent, you should probably create connection and edge types that are specific to that relationship:
type GroupUserConnection {
pageInfo: PageInfo!
egdes: [GroupUserEdge!]!
}
type GroupUserEdge {
cursor: String!
edge: User!
role: Role!
}
This way, you can still use a regular UserConnection for other fields and avoid clients unnecessarily requesting a role where there isn't one.