GroupsResolver.cs

public class GroupsResolver : Resolver, IGroupsResolver
{
    private readonly IGroupsService _groupsService;

    public GroupsResolver(IGroupsService groupsService)
    {
        _groupsService = groupsService;
    }

    public void Resolve(GraphQLQuery graphQLQuery)
    {
        graphQLQuery.Field<ListGraphType<GroupType>>(
            "groups",
            resolve: context => _groupsService.GetGroupsAsync()
        );
    }
}