Specify n argument for dbReadTable() about dbi3 HOT 7 OPEN

The argument can't be named n because there's a conflict with name:

f <- function(name, ..., n = NULL) {
  tibble::lst(name, ..., n)
}

f("a")
#> $name
#> [1] "a"
#> 
#> $n
#> NULL
f(n = "a")
#> Error in eval_tidy(xs[[i]], unique_output): argument "name" is missing, with no default
f(name = "a")
#> $name
#> [1] "a"
#> 
#> $n
#> NULL

^{Created on 2019-08-23 by the reprex package (v0.3.0)}

Going for max_rows and establishing consistency in r-dbi/DBI#235.

from dbi3.

Scratch that: n seems perfectly fine. Still need to understand why the first implementation attempt in RSQLite failed.

f <- function(name, ..., n = NULL) {
  tibble::lst(name, ..., n)
}

f("b")
#> $name
#> [1] "b"
#> 
#> $n
#> NULL
f(n = "a")
#> Error in eval_tidy(xs[[i]], unique_output): argument "name" is missing, with no default
f("b", n = "a")
#> $name
#> [1] "b"
#> 
#> $n
#> [1] "a"
f(n = "a", "b")
#> $name
#> [1] "b"
#> 
#> $n
#> [1] "a"

^{Created on 2019-09-23 by the reprex package (v0.3.0)}

from dbi3.

The problem is partial matching of arguments for backends that don't implement the n argument yet:

library(tibble)

f <- function(name, ...) {
  lst(name, ...)
}

f(3, 1)
#> $name
#> [1] 3
#> 
#> $`1`
#> [1] 1
f(1, name = 3)
#> $name
#> [1] 3
#> 
#> $`1`
#> [1] 1

# Bad
f(1, n = 3)
#> $name
#> [1] 3
#> 
#> $`1`
#> [1] 1

^{Created on 2019-09-23 by the reprex package (v0.3.0)}

from dbi3.

Can solve by declaring the n argument before the ellipsis in the dbReadTable() generic.

from dbi3.

Backends probably want to override this to include LIMIT n or TOP n in the query.

from dbi3.

Postponing, because if we limit rows we also might want to limit columns. This functionality already exists in much better form in dbplyr and other packages.

from dbi3.

The "first n rows" isn't usually a good criterion because the data is returned in an order decided by the server.

from dbi3.