dbDriver("name")

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.

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

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:

I'm not sure if it is a good idea or not to find drivers that are not loaded
or attached. This may cause more problems than it adds simplifications?
Would you load or attach the packages in which the drivers are found? You
and others probably understand the implications better than I do.

Possibly one of my comments initiated the findDriver() effort, so let me
give the context in which I have been doing something a bit similar. I look
through a list of loaded/attached packages for a particular database, with a
function  called like this:

  con <- TSfinddb(dbname="ets",
              driverOrder=c("MySQL", "SQLite", "PostgreSQL"))

which attempts a dbConnect for each driver string, looking for the database
"ets". But I just look though attached or loaded packages and the database
may not exist even if the package is loaded, so I need to wrap the dbConnect
calls in try().