I am using Absinthe to build a GraphQL API. The datastore is Dgraph, which uses GraphQL+ as query language. It is similar to GraphQL but not identical.
This would in theory put me in a wonderful situation. A GraphQL query like
query {
user {
id
username
posts {
title
text
comments {
text
}
}
}
}
could be also just one query in Dgraph. It would look almost identical:
{
users(func: has(type_user))
{
id
username
posts {
title
text
comments {
text
}
}
}
}
This power of graph databases to load complex relations in one go is something that I would like to use. The problem is just: In Absinthe the schema is supposed to be composable. In the schema would have one :user object that has a :posts field which would be a list_of(:post). And then a :post object. Etc. pp.
To help prevent N+1 queries you would use dataloader or batch loading.
Now I could just load everything in one go. I could for example write a resolver that does just that:
defmodule MyApp.Resolvers.User do
alias MyApp.Users
def users(_, _args, _) do
{:ok, Users.all()}
end
end
And the user context that actually queries the db
defmodule MyApp.Users do
alias MyApp.Users.User
def all do
query = """
{
users(func: has(type_user))
{
id
username
posts {
title
text
comments {
text
}
}
}
}
"""
case ExDgraph.query(conn(), query) do
{:ok, msg} ->
%{result: %{users: users}} = msg
Enum.map(users, fn x -> struct(User, x) end)
{:error, _error} ->
[]
end
end
end
The issue here is that I overfetch. I ALWAYS query everything, even if I only want a list of users. This works but is not very good performance wise. And I loose the composability.
What would be a solution is if I had access to the query in the resolver to understand which fields are requested. I could then use pattern matching to build the query and then send it to Dgraph. I could even have one central resolver and many query builders. But I would need to hook into the query and parse it directly.
Is something like that possible? Any idea where I could find something interesting to solve this? Maybe with Absinthe middleware?
Thanks!
