[R-sig-DB] dbDriver("name")

[Hadley Wickham]

>> Thanks for the suggestion, however, I remain a bit confused. The function
>> find_driver() seems like a direct replacement for dbConnect(), using a
>> string to identify the database driver. You would be supporting what is a
>> bad idea, and just changing the name of the function, which is a make work
>> project for everyone.
>
> So unless we want to invent a completely new way of registering
> drivers, it seems like patching dbDriver to use this strategy will be
> effective. However, I think we should equally encourage people to use
> the driver object directly, instead of the string. That doesn't help
> you, but it does help people only concerned with connecting to one
> database.

Here's a first stab at it. I think it should work for the majority of
existing packages, regardless of whether they're loaded or not:

setMethod("dbDriver", "character",
  definition = function(drvName, ...) {
    findDriver(drvName)(...)
  }
)

findDriver <- function(drvName) {
  # If it exists in the global environment, use that
  d <- get2(drvName, globalenv())
  if (!is.null(d)) return(d)

  # Otherwise, see if the appropriately named package is available
  if (has_namespace(drvName)) {
    d <- get2(drvName, asNamespace(drvName))
    if (!is.null(d)) return(d)
  }

  pkgName <- paste0("R", drvName)
  # First, see if package with name R + drvName is available
  if (has_namespace(pkgName)) {
    d <- get2(drvName, asNamespace(pkgName))
    if (!is.null(d)) return(d)
  }

  # Can't find it:
  stop("Couldn't find driver ", drvName, ". Looked in:\n",
    "* global namespace\n",
    "* in package called ", drvName, "\n",
    "* in package called ", pkgName,
    call. = FALSE)
}

get2 <- function(x, env) {
  if (!exists(x, envir = env)) return(NULL)
  get(x, envir = env)
}

has_namespace <- function(x) {
  suppressMessages(requireNamespace(x, quietly = TRUE))
}

Hadley

-- 
Chief Scientist, RStudio
http://had.co.nz/