I'm not sure about PostGraphile, but Hasura I know transforms a graphql request into a SQL request that can return the JSON response expected as part of the Gra

I'm not sure about PostGraphile, but Hasura I know transforms a graphql request into a SQL request that can return the JSON response expected as part of the GraphQL spec. I believe that's the reason that Hasura only works with PostgreSQL, since it has the necessary SQL functions to generate arbitrary JSON objects.