c/driver/postgresql: Support enum type

[paleolimbot]

It looks like the postgres enum type is not quite supported yet, although there is a workaround:

library(adbcdrivermanager)

db <- adbc_database_init(
  adbcpostgresql::adbcpostgresql(),
  uri = "postgresql://localhost:5432/postgres?user=postgres&password=password") 

db |> 
  execute_adbc("CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy')")

db |> 
  adbc_database_release()

# Have to recreate the database after because that's where we cache the types
con <- db <- adbc_database_init(
    adbcpostgresql::adbcpostgresql(),
    uri = "postgresql://localhost:5432/postgres?user=postgres&password=password"
  ) |> 
  adbc_connection_init()

con |> 
  execute_adbc("CREATE TABLE x (a mood)") |> 
  execute_adbc("INSERT INTO x VALUES ('sad')") |> 
  execute_adbc("INSERT INTO x VALUES ('ok')")

# Currently returned as binary (i.e., COPY output)
con |> 
  read_adbc("SELECT * from x") |> 
  as.data.frame() |> 
  dplyr::pull(a) |> 
  unclass() |> 
  vapply(rawToChar, character(1))
#> [1] "sad" "ok"

^{Created on 2024-01-23 with reprex v2.0.2}

[lidavidm]

It would also be good to have a way to purge the cache or notice that we need to rebuild it, hmm