Recursive flattening failure with combined primary and foreign key

[nirski]

When a column serves as both a primary and foreign key, dm refuses to flatten the model. Below is a minimal example.

mydm <- dm(
    x = tibble(a = 1, b = 2),
    y = tibble(c = 2, d = 3),
    z = tibble(e = 2, f = 4)
    ) %>%
    dm_add_pk(x, a) %>%
    dm_add_pk(y, c) %>%
    dm_add_pk(z, e) %>%
    dm_add_fk(x, b, y) %>%
    dm_add_fk(y, c, z)

Diagram:

mydm %>% dm_draw(view_type = "all")

Flattening the model

mydm %>% dm_flatten_to_tbl(x, .recursive = TRUE)

Output:

Error in `join()`:
! Join columns in `x` must be present in the data.
✖ Problem with `c`.
Run `rlang::last_trace()` to see where the error occurred.

Expected output:

# A tibble: 1 × 4
      a     b     d     f
  <dbl> <dbl> <dbl> <dbl>
1     1     2     3     4