Use of return() in tidy style when creating functions with dbplyr

Question

I am trying to figure out how to apply the tidy style guide to some functions I am creating. Specifically I am trying to limit my use of return() - as per the style guide suggestion to only use in the case of early returns - in the context of dbplyr functions. Before reading the style guide I would have done it like this (you need dplyr and dbplyr to run this):

cars_return <- function(){
  con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
  dplyr::copy_to(con, mtcars)

  mtcars2 <- dplyr::tbl(con, "mtcars")

  mtcars2 <- dplyr::collect(mtcars2)

  return(mtcars2)

  DBI::dbDisconnect(con)
}

Which would have returned this:

> cars_return()
# A tibble: 32 x 11
     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
 1  21.0     6 160.0   110  3.90 2.620 16.46     0     1     4     4
 2  21.0     6 160.0   110  3.90 2.875 17.02     0     1     4     4
 3  22.8     4 108.0    93  3.85 2.320 18.61     1     1     4     1
 4  21.4     6 258.0   110  3.08 3.215 19.44     1     0     3     1
 5  18.7     8 360.0   175  3.15 3.440 17.02     0     0     3     2
 6  18.1     6 225.0   105  2.76 3.460 20.22     1     0     3     1
 7  14.3     8 360.0   245  3.21 3.570 15.84     0     0     3     4
 8  24.4     4 146.7    62  3.69 3.190 20.00     1     0     4     2
 9  22.8     4 140.8    95  3.92 3.150 22.90     1     0     4     2
10  19.2     6 167.6   123  3.92 3.440 18.30     1     0     4     4
# ... with 22 more rows

However if I try to omit return() like this:

cars_no_return <- function(){
  con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
  dplyr::copy_to(con, mtcars)

  mtcars2 <- dplyr::tbl(con, "mtcars")

  dplyr::collect(mtcars2)

  DBI::dbDisconnect(con)
}

Then when i call that function, I get nothing returned:

> cars_no_return()
>

So my question is, how do I deal with functions that need to return a data.frame from a database using collect() while respecting the tidy style guide.

Answer 1

You should look into on.exit. Eg see How and when should I use on.exit?

cars_return <- function(){
  con <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")

  on.exit(DBI::dbDisconnect(con))

  dplyr::copy_to(con, mtcars)

  mtcars2 <- dplyr::tbl(con, "mtcars")

  mtcars2 <- dplyr::collect(mtcars2)

  mtcars2
}