Excessive joins within nested polymorphic table

[Luke265]

Summary

In the reproduction provided below, the Task and TaskTimeline tables utilize polymorphic relationships (relational and unionMember modes, respectively).

When querying the TaskComment file, the generated SQL contains one identical File join for every Task type. For example, if there are 4 Task types, the generated query includes 4 identical joins to the same File table.

Steps to reproduce

benjie/ouch#46
run query:

query {
  allTasks {
    nodes {
      taskTimelinesByTaskId {
        nodes {
          item {
            ... on TaskComment {
              content
              taskCommentFilesByTaskCommentId {
                nodes {
                  fileByFileId {
                    id
                  }
                }
              }
            }
          }
        }
      }
    }
  }
}

Expected results

expected query for TaskComment:

select
  __task_comment__."content" as "0",
  __task_comment__."id"::text as "1",
  array(
    select array[
      __task_comment_file__."file_id"::text,
      __file__."id"::text
    ]::text[]
    from "public"."task_comment_file" as __task_comment_file__
    left outer join "public"."file" as __file__
    on (
    /* WHERE becoming ON */ (
      __file__."id" = __task_comment_file__."file_id"
    ))
    where (
      __task_comment_file__."task_comment_id" = __task_comment__."id"
    )
    order by __task_comment_file__."id" asc
  )::text as "2"
from "public"."task_comment" as __task_comment__
where (
  __task_comment__."id" = $1::"int4"
);

Actual results

select
  __task_comment__."content" as "0",
  __task_comment__."id"::text as "1",
  array(
    select array[
      __task_comment_file__."file_id"::text,
      __file__."id"::text,
      __file_2."id"::text,
      __file_3."id"::text,
      __file_4."id"::text
    ]::text[]
    from "public"."task_comment_file" as __task_comment_file__
    left outer join "public"."file" as __file__
    on (
    /* WHERE becoming ON */ (
      __file__."id" = __task_comment_file__."file_id"
    ))
    left outer join "public"."file" as __file_2
    on (
    /* WHERE becoming ON */ (
      __file_2."id" = __task_comment_file__."file_id"
    ))
    left outer join "public"."file" as __file_3
    on (
    /* WHERE becoming ON */ (
      __file_3."id" = __task_comment_file__."file_id"
    ))
    left outer join "public"."file" as __file_4
    on (
    /* WHERE becoming ON */ (
      __file_4."id" = __task_comment_file__."file_id"
    ))
    where (
      __task_comment_file__."task_comment_id" = __task_comment__."id"
    )
    order by __task_comment_file__."id" asc
  )::text as "2"
from "public"."task_comment" as __task_comment__
where (
  __task_comment__."id" = $1::"int4"
);

[benjie]

Thanks for the repro 👍